### Publications BibTex file

 @article{Balocco2012, title = {Building-plant system energy sustainability. An approach for transient thermal performance analysis}, author = {Carla Balocco and Virginia Gori and Enrico Marmonti and Luca Citi}, journal = {Energy and Buildings}, year = {2012}, month = jun, pages = {443--453}, volume = {49}, abstract = {The aim of this research is to investigate the thermophysical behaviour of building envelope multi-layer components and assess the whole building-plant response. The investigation was carried out in two different phases. The first phase concerned the study of the dynamic response of building envelope multi-layer components, by providing an improved implementation of the present European Standard UNI EN ISO 13786:2008. The proposed method allows one to determine the transient thermophysical performance of opaque building components that are associated with a thermal zone maintained at constant or variable air temperature. The variable internal air temperature can be associated with experimental data. The second phase consisted of a transient analysis of the above thermal zone with a conditioning plant working. The building plant simulations were carried out by EnergyPlus software. The method proposed, based on European standards, is particularly useful in the perspective of the Certification of the Energy Performance of the building-plant system, required by the European Union. It can provide a useful tool for developing an abacus of different envelope multi-layer component performances in order to support design choices.}, check = {2012.09.26}, doi = {10.1016/j.enbuild.2012.02.048}, owner = {lciti}, timestamp = {2012.03.28} }  @article{Burykin2014DynDensityDelayMaps, title = {Dynamical density delay maps: simple, new method for visualising the behaviour of complex systems}, author = {Anton Burykin and Madalena D Costa and Luca Citi and Ary L Goldberger}, journal = {BMC Medical Informatics and Decision Making}, year = {2014}, month = jan, number = {6}, pages = {1--8}, volume = {14}, abstract = {Background. Physiologic signals, such as cardiac interbeat intervals, exhibit complex fluctuations. However, capturing important dynamical properties, including nonstationarities may not be feasible from conventional time series graphical representations. Methods. We introduce a simple-to-implement visualisation method, termed dynamical density delay mapping (D3-Map'' technique) that provides an animated representation of a system's dynamics. The method is based on a generalization of conventional two-dimensional (2D) Poincar\'e plots, which are scatter plots where each data point, x(n), in a time series is plotted against the adjacent one, x(n+1). First, we divide the original time series, x(n) (n=1,..., N), into a sequence of segments (windows). Next, for each segment, a three-dimensional (3D) Poincar\'e surface plot of x(n), x(n+1), h[x(n),x(n+1)] is generated, in which the third dimension, h, represents the relative frequency of occurrence of each (x(n),x(n+1)) point. This 3D Poincar\'e surface is then chromatised by mapping the relative frequency h values onto a colour scheme. We also generate a colourised 2D contour plot from each time series segment using the same colourmap scheme as for the 3D Poincar\'e surface. Finally, the original time series graph, the colourised 3D Poincar\'e surface plot, and its projection as a colourised 2D contour map for each segment, are animated to create the full D3-Map.'' Results. We first exemplify the D3-Map method using the cardiac interbeat interval time series from a healthy subject during sleeping hours. The animations uncover complex dynamical changes, such as transitions between states, and the relative amount of time the system spends in each state. We also illustrate the utility of the method in detecting hidden temporal patterns in the heart rate dynamics of a patient with atrial fibrillation. The videos, as well as the source code, are made publicly available. Conclusions. Animations based on density delay maps provide a new way of visualising dynamical properties of complex systems not apparent in time series graphs or standard Poincar\'e plot representations. Trainees in a variety of fields may find the animations useful as illustrations of fundamental but challenging concepts, such as nonstationarity and multistability. For investigators, the method may facilitate data exploration.}, check = {2014.01.23}, doi = {10.1186/1472-6947-14-6}, owner = {lciti}, publisher = {BioMed Central Ltd}, timestamp = {2015.01.22} }  @article{Citi2014LikelihoodMethodsPointProcRefract, title = {Likelihood Methods for Point Processes with Refractoriness}, author = {Citi, Luca and Ba, Demba and Brown, Emery N and Barbieri, Riccardo}, journal = {Neural Computation}, year = {2014}, number = {2}, pages = {237--263}, volume = {26}, abstract = {Likelihood-based encoding models founded on point processes have received significant attention in the literature because of their ability to reveal the information encoded by spiking neural populations. We propose an approximation to the likelihood of a point-process model of neurons that holds under assumptions about the continuous time process that are physiologically reasonable for neural spike trains: the presence of a refractory period, the predictability of the conditional intensity function, and its integrability. These are properties that apply to a large class of point processes arising in applications other than neuroscience. The proposed approach has several advantages over conventional ones. In particular, one can use standard fitting procedures for generalized linear models based on iteratively reweighted least squares while improving the accuracy of the approximation to the likelihood and reducing bias in the estimation of the parameters of the underlying continuous-time model. As a result, the proposed approach can use a larger bin size to achieve the same accuracy as conventional approaches would with a smaller bin size. This is particularly important when analyzing neural data with high mean and instantaneous firing rates. We demonstrate these claims on simulated and real neural spiking activity. By allowing a substantive increase in the required bin size, our algorithm has the potential to lower the barrier to the use of point-process methods in an increasing number of applications.}, check = {2015.01.22}, doi = {10.1162/NECO_a_00548}, owner = {lciti}, timestamp = {2015.01.22}, url = {http://users.neurostat.mit.edu/lciti/publications_files/Citi2014LikelihoodMethodsPointProcRefract_preprint.pdf} }  @article{Citi2012DetectCorrectErronBeats, title = {A real-time automated point-process method for the detection and correction of erroneous and ectopic heartbeats.}, author = {Luca Citi and Emery N Brown and Riccardo Barbieri}, journal = {IEEE Transactions on Biomedical Engineering}, year = {2012}, month = oct, number = {10}, pages = {2828--2837}, volume = {59}, abstract = {The presence of recurring arrhythmic events (also known as cardiac dysrhythmia or irregular heartbeats), as well as erroneous beat detection due to low signal quality, significantly affects estimation of both time and frequency domain indices of heart rate variability (HRV). A reliable, real-time classification and correction of ECG-derived heartbeats is a necessary prerequisite for an accurate online monitoring of HRV and cardiovascular control. We have developed a novel point-process-based method for real-time R-R interval error detection and correction. Given an R-wave event, we assume that the length of the next R-R interval follows a physiologically motivated, time-varying inverse Gaussian probability distribution. We then devise an instantaneous automated detection and correction procedure for erroneous and arrhythmic beats by using the information on the probability of occurrence of the observed beat provided by the model. We test our algorithm over two datasets from the PhysioNet archive. The Fantasia normal rhythm database is artificially corrupted with known erroneous beats to test both the detection procedure and correction procedure. The benchmark MIT-BIH Arrhythmia database is further considered to test the detection procedure of real arrhythmic events and compare it with results from previously published algorithms. Our automated algorithm represents an improvement over previous procedures, with best specificity for the detection of correct beats, as well as highest sensitivity to missed and extra beats, artificially misplaced beats, and for real arrhythmic events. A near-optimal heartbeat classification and correction, together with the ability to adapt to time-varying changes of heartbeat dynamics in an online fashion, may provide a solid base for building a more reliable real-time HRV monitoring device.}, check = {2012.09.26}, doi = {10.1109/TBME.2012.2211356}, owner = {lciti}, pmid = {22875239}, timestamp = {2012.09.26}, url = {http://users.neurostat.mit.edu/lciti/publications_files/Citi2012DetectCorrectErronBeats.pdf} }  @article{Citi2008UseWavDenAndSpikeSortingProcessENGSignals, title = {On the use of wavelet denoising and spike sorting techniques to process electroneurographic signals recorded using intraneural electrodes.}, author = {Luca Citi and Jacopo Carpaneto and Ken Yoshida and Klaus-Peter Hoffmann and Klaus Peter Koch and Paolo Dario and Silvestro Micera}, journal = {Journal of Neuroscience Methods}, year = {2008}, month = jul, number = {2}, pages = {294--302}, volume = {172}, abstract = {Among the possible interfaces with the peripheral nervous system (PNS), intraneural electrodes represent an interesting solution for their potential advantages such as the possibility of extracting spikes from electroneurographic (ENG) signals. Their use could increase the precision and the amount of information which can be detected with respect to other processing methods. In this study, in order to verify this assumption, thin-film longitudinal intrafascicular electrodes (tfLIFE) were implanted in the sciatic nerve of rabbits. Various sensory stimuli were applied to the hind limb of the animal and the elicited ENG signals were recorded using the tfLIFEs. These signals were processed to determine whether the different types of information can be decoded. Signals were wavelet denoised and spike sorted. Support vector machines were trained to use the spike waveforms found to infer the stimulus applied to the rabbit. This approach was also compared with previously used ENG-processing methods. The results indicate that the combination of wavelet denoising and spike sorting techniques can increase the amount of information extractable from ENG signals recorded with intraneural electrodes. This strategy could allow the development of more effective closed-loop neuroprostheses and hybrid bionic systems connecting the human nervous system with artificial devices.}, aka = {#Citi2007UseLIFEsIdentifyNeuralInformation#}, check = {2011.01.12}, doi = {10.1016/j.jneumeth.2008.04.025}, institution = {ARTS and CRIM Labs, Scuola Superiore Sant'Anna, Pisa, Italy.}, owner = {lciti}, pii = {S0165-0270(08)00258-6}, pmid = {18534683}, timestamp = {2008.09.07}, url = {http://users.neurostat.mit.edu/lciti/publications_files/Citi2008WaveletDenoisingSpikeSorting.pdf} }  @article{Citi2010DocumenModelExploitP300AmplVar, title = {Documenting, modelling and exploiting {P300} amplitude changes due to variable target delays in {D}onchin's speller.}, author = {Luca Citi and Riccardo Poli and Caterina Cinel}, journal = {Journal of Neural Engineering}, year = {2010}, month = oct, number = {5}, pages = {056006}, volume = {7}, abstract = {The P300 is an endogenous event-related potential (ERP) that is naturally elicited by rare and significant external stimuli. P300s are used increasingly frequently in brain-computer interfaces (BCIs) because the users of ERP-based BCIs need no special training. However, P300 waves are hard to detect and, therefore, multiple target stimulus presentations are needed before an interface can make a reliable decision. While significant improvements have been made in the detection of P300s, no particular attention has been paid to the variability in shape and timing of P300 waves in BCIs. In this paper we start filling this gap by documenting, modelling and exploiting a modulation in the amplitude of P300s related to the number of non-targets preceding a target in a Donchin speller. The basic idea in our approach is to use an appropriately weighted average of the responses produced by a classifier during multiple stimulus presentations, instead of the traditional plain average. This makes it possible to weigh more heavily events that are likely to be more informative, thereby increasing the accuracy of classification. The optimal weights are determined through a mathematical model that precisely estimates the accuracy of our speller as well as the expected performance improvement w.r.t. the traditional approach. Tests with two independent datasets show that our approach provides a marked statistically significant improvement in accuracy over the top-performing algorithm presented in the literature to date. The method and the theoretical models we propose are general and can easily be used in other P300-based BCIs with minimal changes.}, check = {2011.01.12}, doi = {10.1088/1741-2560/7/5/056006}, institution = {Brain-Computer Interfaces Lab, School of Computer Science and Electronic Engineering,University of Essex, Colchester CO4 3SQ, UK. lciti@neurostat.mit.edu}, owner = {lciti}, pii = {S1741-2560(10)59095-5}, pmid = {20811092}, timestamp = {2010.10.27}, url = {http://users.neurostat.mit.edu/lciti/publications_files/Citi2010DocumenModelExploitP300AmplVar.pdf} }  @article{Citi2008P300BCIMouseGenetOptimAnalogueContr, title = {P300-based {BCI} Mouse with Genetically-optimized Analogue Control}, author = {Luca Citi and Riccardo Poli and Francisco Sepulveda and Caterina Cinel}, journal = {IEEE Transactions on Neural System and Rehabilitation Engineering}, year = {2008}, month = feb, number = {1}, pages = {51--61}, volume = {16}, abstract = {In this paper we propose a brain-computer interface (BCI) mouse based on P300 waves in electroencephalogram (EEG) signals. The system is analogue in that at no point a binary decision is made as to whether or not a P300 was actually produced in response to the stimuli. Instead, the 2-D motion of the pointer on the screen, using a novel BCI paradigm, is controlled by directly combining the amplitudes of the output produced by a filter in the presence of different stimuli. This filter and the features to be combined within it are optimised by an evolutionary algorithm.}, check = {2011.01.12}, doi = {10.1109/TNSRE.2007.913184}, institution = {IMT Institute for Advanced Studies, 55100 Lucca, Italy. lciti@essex.ac.uk}, keywords = {Adult; Algorithms; Brain, physiology; Computer Graphics; Electrodes; Electroencephalography; Event-Related Potentials, P300, genetics/physiology; Female; Humans; Male; Psychomotor Performance, physiology; User-Computer Interface}, owner = {lciti}, pmid = {18303806}, timestamp = {2006.11.26}, url = {http://users.neurostat.mit.edu/lciti/publications_files/Citi2008P300BasedBCIMouse.pdf} }  @article{Citi2009MatchingBMIPerfSpaceAppl, title = {Matching {Brain-Machine Interface} performance to space applications}, author = {Luca Citi and Oliver Tonet and Martina Marinelli}, journal = {International Review of Neurobiology}, year = {2009}, month = jul, pages = {199--212}, volume = {86}, abstract = {A brain-machine interface (BMI) is a particular class of human-machine interface (HMI). BMIs have so far been studied mostly as a communication means for people who have little or no voluntary control of muscle activity. For able-bodied users, such as astronauts, a BMI would only be practical if conceived as an augmenting interface. A method is presented for pointing out effective combinations of HMIs and applications of robotics and automation to space. Latency and throughput are selected as performance measures for a hybrid bionic system (HBS), that is, the combination of a user, a device, and a HMI. We classify and briefly describe HMIs and space applications and then compare the performance of classes of interfaces with the requirements of classes of applications, both in terms of latency and throughput. Regions of overlap correspond to effective combinations. Devices requiring simpler control, such as a rover, a robotic camera, or environmental controls are suitable to be driven by means of BMI technology. Free flyers and other devices with six degrees of freedom can be controlled, but only at low-interactivity levels. More demanding applications require conventional interfaces, although they could be controlled by BMIs once the same levels of performance as currently recorded in animal experiments are attained. Robotic arms and manipulators could be the next frontier for noninvasive BMIs. Integrating smart controllers in HBSs could improve interactivity and boost the use of BMI technology in space applications.}, check = {2011.01.12}, doi = {10.1016/S0074-7742(09)86015-7}, institution = {School of Computer Science and Electronic Engineering, University of Essex, Wivenhoe Park, CO4 3SQ Colchester, UK.}, keywords = {Brain, physiology; Communication Aids for Disabled; Humans; Man-Machine Systems; Psychomotor Performance, physiology; Reaction Time, physiology; Space Flight; User-Computer Interface}, owner = {lciti}, pii = {S0074-7742(09)86015-7}, pmid = {19608001}, timestamp = {2009.05.13}, url = {http://users.neurostat.mit.edu/lciti/publications_files/Citi2009MatchingBMIPerfSpaceAppl.pdf} }  @article{Ciulli2016, title = {Prediction of Impaired Performance in Trail Making Test in MCI Patients With Small Vessel Disease Using DTI Data.}, author = {Ciulli, Stefano and Citi, Luca and Salvadori, Emilia and Valenti, Raffaella and Poggesi, Anna and Inzitari, Domenico and Mascalchi, Mario and Toschi, Nicola and Pantoni, Leonardo and Diciotti, Stefano}, journal = {IEEE Journal of Biomedical and Health Informatics}, year = {2016}, month = jul, number = {4}, pages = {1026--1033}, volume = {20}, __markedentry = {[lciti:]}, abstract = {Mild cognitive impairment (MCI) is a common condition in patients with diffuse hyperintensities of cerebral white matter (WM) in T2-weighted magnetic resonance images and cerebral small vessel disease (SVD). In MCI due to SVD, the most prominent feature of cognitive impairment lies in degradation of executive functions, i.e., of processes that supervise the organization and execution of complex behavior. The trail making test is a widely employed test sensitive to cognitive processing speed and executive functioning. MCI due to SVD has been hypothesized to be the effect of WM damage, and diffusion tensor imaging (DTI) is a well-established technique for in vivo characterization of WM. We propose a machine learning scheme tailored to 1) predicting the impairment in executive functions in patients with MCI and SVD, and 2) examining the brain substrates of this impairment. We employed data from 40 MCI patients with SVD and created feature vectors by averaging mean diffusivity (MD) and fractional anisotropy maps within 50 WM regions of interest. We trained support vector machines (SVMs) with polynomial as well as radial basis function kernels using different DTI-derived features while simultaneously optimizing parameters in leave-one-out nested cross validation. The best performance was obtained using MD features only and linear kernel SVMs, which were able to distinguish an impaired performance with high sensitivity (72.7\%-89.5\%), specificity (71.4\%-83.3\%), and accuracy (77.5\%-80.0\%). While brain substrates of executive functions are still debated, feature ranking confirm that MD in several WM regions, not limited to the frontal lobes, are truly predictive of executive functions.}, doi = {10.1109/JBHI.2016.2537808}, language = {eng}, medline-pst = {ppublish}, owner = {lciti}, pmid = {26960231}, timestamp = {2016.10.17} }  @article{Greco2016SkinAdmittanceMeasurement, title = {Skin Admittance Measurement for Emotion Recognition: A Study over Frequency Sweep}, author = {Greco, Alberto and Lanata, Antonio and Citi, Luca and Vanello, Nicola and Valenza, Gaetano and Scilingo, Enzo Pasquale}, journal = {Electronics}, year = {2016}, number = {3}, pages = {46}, volume = {5}, abstract = {The electrodermal activity (EDA) is a reliable physiological signal for monitoring the sympathetic nervous system. Several studies have demonstrated that EDA can be a source of effective markers for the assessment of emotional states in humans. There are two main methods for measuring EDA: endosomatic (internal electrical source) and exosomatic (external electrical source). Even though the exosomatic approach is the most widely used, differences between alternating current (AC) and direct current (DC) methods and their implication in the emotional assessment field have not yet been deeply investigated. This paper aims at investigating how the admittance contribution of EDA, studied at different frequency sources, affects the EDA statistical power in inferring on the subject's arousing level (neutral or aroused). To this extent, 40 healthy subjects underwent visual affective elicitations, including neutral and arousing levels, while EDA was gathered through DC and AC sources from 0 to 1 kHz. Results concern the accuracy of an automatic, EDA feature-based arousal recognition system for each frequency source. We show how the frequency of the external electrical source affects the accuracy of arousal recognition. This suggests a role of skin susceptance in the study of affective stimuli through electrodermal response.}, doi = {10.3390/electronics5030046}, owner = {lciti}, publisher = {Multidisciplinary Digital Publishing Institute} }  @article{Greco2017ArousalValenceRecognAffectiveSounds, title = {Arousal and Valence Recognition of Affective Sounds Based on Electrodermal Activity}, author = {A. Greco and G. Valenza and L. Citi and E. P. Scilingo}, journal = {IEEE Sensors Journal}, year = {2017}, month = feb, number = {3}, pages = {716-725}, volume = {17}, abstract = {Physiological sensors and interfaces for mental healthcare are becoming of great interest in research and commercial fields. Specifically, biomedical sensors and related ad hoc signal processing methods can be profitably used for supporting objective, psychological assessments. However, a simple system able to automatically classify the emotional state of a healthy subject is still missing. To overcome this important limitation, we here propose the use of convex optimization-based electrodermal activity (EDA) framework and clustering algorithms to automatically discern arousal and valence levels induced by affective sound stimuli. EDA recordings were gathered from 25 healthy volunteers, using only one EDA sensor to be placed on fingers. Standardized stimuli were chosen from the International Affective Digitized Sound System database, and grouped into four different levels of arousal (i.e., the levels of emotional intensity) and two levels of valence (i.e., how unpleasant/pleasant a sound can be perceived). Experimental results demonstrated that our system is able to achieve a recognition accuracy of 77.33% on the arousal dimension, and 84% on the valence dimension.}, doi = {10.1109/JSEN.2016.2623677}, issn = {1530-437X}, keywords = {bioelectric phenomena;health care;medical signal processing;skin;statistical analysis;EDA recordings;International Affective Digitized Sound System database;affective sounds;arousal recognition;biomedical sensors;clustering algorithm;convex optimization based electrodermal activity;mental healthcare;physiological sensors;psychological assessment;valence recognition;Audio systems;Autoregressive processes;Extraterrestrial measurements;Feature extraction;Pattern recognition;Sensors;Skin;Electrodermal activity;K-NN classifier;affective digitized sound system (IADS);convex optimization;electrodermal response;emotion recognition;sparse representation} }  @article{Greco2015cvxEDA, title = {{cvxEDA}: a Convex Optimization Approach to Electrodermal Activity Processing}, author = {Greco, Alberto and Valenza, Gaetano and Lanata, Antonio and Scilingo, Enzo Pasquale and Citi, Luca}, journal = {IEEE Transactions on Biomedical Engineering}, year = {2015}, month = aug, abstract = {This paper reports on a novel algorithm for the analysis of electrodermal activity (EDA) using methods of convex optimization. EDA can be considered one of the most common observation channels of sympathetic nervous system activity, and manifests itself as a change in electrical properties of the skin, such as skin conductance (SC). The proposed model describes SC as the sum of three terms: the phasic component, the tonic component, and an additive white Gaussian noise term incorporating model prediction errors as well as measurement errors and artifacts. This model is physiologically inspired and fully explains EDA through a rigorous methodology based on Bayesian statistics, mathematical convex optimization and sparsity. The algorithm was evaluated in three different experimental sessions to test its robustness to noise, its ability to separate and identify stimulus inputs, and its capability of properly describing the activity of the autonomic nervous system in response to strong affective stimulation. Results are very encouraging, showing good performance of the proposed method and suggesting promising future applicability, e.g. in the field of affective computing.}, doi = {10.1109/TBME.2015.2474131}, owner = {lciti}, timestamp = {2015.08.28}, url = {http://users.neurostat.mit.edu/lciti/publications_files/Greco2015cvxEDA.pdf} }  @article{Greco2016ForceVelocityAssessmentCaress, title = {Force--Velocity Assessment of Caress-Like Stimuli Through the Electrodermal Activity Processing: Advantages of a Convex Optimization Approach}, author = {A. Greco and G. Valenza and M. Nardelli and M. Bianchi and L. Citi and E. P. Scilingo}, journal = {IEEE Transactions on Human-Machine Systems}, year = {2017}, month = feb, number = {1}, pages = {91-100}, volume = {47}, abstract = {We propose the use of the convex optimization-based EDA (cvxEDA) framework to automatically characterize the force and velocity of caressing stimuli through the analysis of the electrodermal activity (EDA). CvxEDA, in fact, solves a convex optimization problem that always guarantees the globally optimal solution. We show that this approach is especially suitable for the implementation in wearable monitoring systems, being more computationally efficient than a widely used EDA processing algorithm. In addition, it ensures low-memory consumption, due to a sparse representation of the EDA phasic components. EDA recordings were gathered from 32 healthy subjects (16 females) who participated in an experiment where a fabric-based wearable haptic system conveyed them caress-like stimuli by means of two motors. Six types of stimuli (combining three levels of velocity and two of force) were randomly administered over time. Performance was evaluated in terms of execution time of the algorithm, memory usage, and statistical significance in discerning the affective stimuli along force and velocity dimensions. Experimental results revealed good performance of cvxEDA model for all of the considered metrics.}, doi = {10.1109/THMS.2016.2586478}, issn = {2168-2291}, keywords = {convex programming;haptic interfaces;statistical analysis;EDA phasic components;EDA processing algorithm;EDA recordings;caress like stimuli;convex optimization approach;convex optimization problem;cvxEDA;electrodermal activity;electrodermal activity processing;fabric based wearable haptic system;force velocity assessment;globally optimal solution;statistical significance;wearable monitoring systems;Autoregressive processes;Biomedical monitoring;Convex functions;Europe;Force;Haptic interfaces;Robots;Affective haptics;CT fibers;caressing stimuli;convex optimization;electrodermal activity;electrodermal response;sparse representation;wearable haptics}, owner = {lciti}, timestamp = {2017.06.02} }  @article{Menon2009ProspectsBMISpaceControl, title = {Prospects of brain-machine interfaces for space system control}, author = {Carlo Menon and Cristina de Negueruela and del R. Mill\'an, Jos\'e and Oliver Tonet and Federico Carpi and Michael Broschart and Pierre Ferrez and Anna Buttfield and Franca Tecchio and Francisco Sepulveda and Luca Citi and Cecilia Laschi and Mario Tombini and Paolo Dario and Paolo Maria Rossini and Danilo De Rossi}, journal = {Acta Astronautica}, year = {2009}, month = feb, number = {4}, pages = {448--456}, volume = {64}, abstract = {The dream of controlling and guiding computer-based systems using human brain signals has slowly but steadily become a reality. The available technology allows real-time implementation of systems that measure neuronal activity, convert their signals, and translate their output for the purpose of controlling mechanical and electronic systems. This paper describes the state of the art of non-invasive brain-machine interfaces (BMIs) and critically investigates both the current technological limits and the future potential that BMIs have for space applications. We present an assessment of the advantages that BMIs can provide and justify the preferred candidate concepts for space applications together with a vision of future directions for their implementation.}, check = {2011.08.17}, doi = {10.1016/j.actaastro.2008.09.008}, issn = {0094-5765}, keywords = {Brain}, owner = {lciti}, timestamp = {2010.10.28}, url = {http://users.neurostat.mit.edu/lciti/publications_files/Menon2009ProspectsBMISpaceControl.pdf} }  @article{Micera2010DecodingFromIntraneuralElect, title = {Decoding Information From Neural Signals Recorded Using Intraneural Electrodes: Toward the Development of a Neurocontrolled Hand Prosthesis}, author = {Micera, S. and Citi, L. and Rigosa, J. and Carpaneto, J. and Raspopovic, S. and Di Pino, G. and Rossini, L. and Yoshida, K. and Denaro, L. and Dario, P. and Rossini, P.M.}, journal = {Proceedings of the IEEE}, year = {2010}, month = mar, number = {3}, pages = {407 -417}, volume = {98}, abstract = {The possibility of controlling dexterous hand prostheses by using a direct connection with the nervous system is particularly interesting for the significant improvement of the quality of life of patients, which can derive from this achievement. Among the various approaches, peripheral nerve based intrafascicular electrodes are excellent neural interface candidates, representing an excellent compromise between high selectivity and relatively low invasiveness. Moreover, this approach has undergone preliminary testing in human volunteers and has shown promise. In this paper, we investigate whether the use of intrafascicular electrodes can be used to decode multiple sensory and motor information channels with the aim to develop a finite state algorithm that may be employed to control neuroprostheses and neurocontrolled hand prostheses. The results achieved both in animal and human experiments show that the combination of multiple sites recordings and advanced signal processing techniques (such as wavelet denoising and spike sorting algorithms) can be used to identify both sensory stimuli (in animal models) and motor commands (in a human volunteer). These findings have interesting implications, which should be investigated in future experiments.}, check = {2010.10.27}, doi = {10.1109/JPROC.2009.2038726}, issn = {0018-9219}, keywords = {animal models;decoding information;dexterous hand prosthesis;electroneurographic signals;finite state algorithm;hybrid bionic systems;intrafascicular electrodes;intraneural electrodes;motor information channels;multiple sensory;nervous system;neural interface;neural signal recording;neurocontrolled hand prosthesis;peripheral nerve;sensory stimuli;signal processing techniques;spike sorting algorithms;wavelet denoising;biomedical electrodes;brain models;decoding;electroencephalography;electromyography;mechanoception;medical robotics;medical signal processing;neurophysiology;prosthetics;sensory aids;signal denoising;sorting;wavelet transforms;}, owner = {lciti}, timestamp = {2010.10.27}, url = {http://users.neurostat.mit.edu/lciti/publications_files/Micera2010DecodingFromIntraneuralElect.pdf} }  @article{Micera2008UseIntranPeriphInterfContrCybernHandProstAmp, title = {On the use of longitudinal intrafascicular peripheral interfaces for the control of cybernetic hand prostheses in amputees.}, author = {Silvestro Micera and Xavier Navarro and Jacopo Carpaneto and Luca Citi and Oliver Tonet and Rossini, Paolo Maria and Carrozza, Maria Chiara and Klaus-Peter Hoffmann and M. Viv\'o and Ken Yoshida and Paolo Dario}, journal = {IEEE Transactions on Neural System and Rehabilitation Engineering}, year = {2008}, month = oct, number = {5}, pages = {453--472}, volume = {16}, abstract = {Significant strides have been recently made to develop highly sensorized cybernetic prostheses aimed at restoring sensorimotor limb functions to those who have lost them because of a traumatic event (amputation). In these cases, one of the main goals is to create a bidirectional link between the artificial devices (e.g., robotic hands, arms, or legs) and the nervous system. Several human-machine interfaces (HMIs) are currently used to this aim. Among them, interfaces with the peripheral nervous system and in particular longitudinal intrafascicular electrodes can be a promising solution able to improve the current situation. In this paper, the potentials and limits of the use of this interface to control robotic devices are presented. Specific information is provided on: 1) the neurophysiological bases for the use peripheral nerve interfaces; 2) a comparison of the potentials of the different peripheral neural interfaces; 3) the possibility of extracting and appropriately interpreting the neural code for motor commands and of delivering sensory feedback by stimulating afferent fibers by using longitudinal intrafascicular electrodes; 4) a preliminary comparative analysis of the performance of this approach with the ones of others HMIs; 5) the open issues which have to be addressed for a chronic usability of this approach.}, check = {2010.10.27}, doi = {10.1109/TNSRE.2008.2006207}, institution = {ARTS and CRIM Laboratories, Scuola Superiore SantAnna, 56127 Pisa, Italy. micera@sssup.it}, keywords = {Amputees, rehabilitation; Cybernetics, instrumentation; Electromyography, instrumentation; Equipment Design; Equipment Failure Analysis; Hand; Humans; Peripheral Nerves, physiology; Prostheses and Implants; Robotics, instrumentation}, owner = {lciti}, pmid = {18990649}, timestamp = {2006.11.27} }  @article{Micera2011DecodingGraspingInfoFronNeuralignals, title = {Decoding of grasping information from neural signals recorded using peripheral intrafascicular interfaces.}, author = {Silvestro Micera and Paolo M Rossini and Jacopo Rigosa and Luca Citi and Jacopo Carpaneto and Stanisa Raspopovic and Mario Tombini and Christian Cipriani and Giovanni Assenza and Maria C Carrozza and Klaus-Peter Hoffmann and Ken Yoshida and Xavier Navarro and Paolo Dario}, journal = {Journal of Neuroengineering and Rehabilitation}, year = {2011}, month = sep, number = {1}, pages = {53}, volume = {8}, abstract = {BACKGROUND: The restoration of complex hand functions by creating a novel bidirectional link between the nervous system and a dexterous hand prosthesis is currently pursued by several groups. This connection must be fast, intuitive, and quite natural to allow an effective bidirectional flow of information between the user's nervous system and the smart artificial device. This goal can be achieved with several approaches and among them, the use of implantable interfaces with the peripheral nervous system, namely intrafascicular electrodes, is considered particularly interesting. METHODS: Thin-film longitudinal intra-fascicular electrodes were implanted in the median and ulnar nerves of an amputee's residuum during a four-week trial. The possibility of decoding motor commands suitable to control a dexterous hand prosthesis was investigated for the first time in this research field by implementing a spike sorting and classification algorithm. RESULTS: The results showed that motor information (e.g., grip types and single finger movements) could be extracted with classification accuracy around 85 (for three classes plus rest) and that the user could improve his ability to govern motor commands over time as shown by the improved discrimination ability of our classification algorithm. CONCLUSIONS: These results open up new and promising possibilities for the development of a neuro-controlled hand prosthesis.}, check = {2011.09.07}, doi = {10.1186/1743-0003-8-53}, owner = {lciti}, pii = {1743-0003-8-53}, pmid = {21892926}, timestamp = {2011.09.07} }  @article{Pani2016RealTimeNeuralSignals, title = {Real-time neural signals decoding onto off-the-shelf DSP processors for neuroprosthetic applications.}, author = {Pani, Danilo and Barabino, Gianluca and Citi, Luca and Meloni, Paolo and Raspopovich, Stanisa and Micera, Silvestro and Raffo, Luigi}, journal = {IEEE Transactions on Neural System and Rehabilitation Engineering}, year = {2016}, month = sep, number = {9}, pages = {993--1002}, volume = {2}, abstract = {The control of upper limb neuroprostheses through the peripheral nervous system (PNS) can allow restoring motor functions in amputees. At present, the important aspect of the real-time implementation of neural decoding algorithms on embedded systems has been often overlooked, notwithstanding the impact that limited hardware resources have on the efficiency/effectiveness of any given algorithm. Present study is addressing the optimization of a template matching based algorithm for PNS signals decoding that is a milestone for its real-time, full implementation onto a floating-point Digital Signal Processor (DSP). The proposed optimized real-time algorithm achieves up to 96\% of correct classification on real PNS signals acquired through LIFE electrodes on animals, and can correctly sort spikes of a synthetic cortical dataset with sufficiently uncorrelated spike morphologies (93\% average correct classification) comparably to the results obtained with top spike sorter (94\% on average on the same dataset). The power consumption enables more than 24 hours processing at the maximum load, and latency model has been derived to enable a fair performance assessment. The final embodiment demonstrates the real-time performance onto a low-power off-the-shelf DSP, opening to experiments exploiting the efferent signals to control a motor neuroprosthesis.}, doi = {10.1109/TNSRE.2016.2527696}, language = {eng}, medline-pst = {aheadofprint}, owner = {lciti}, pmid = {27164593}, timestamp = {2016.10.17}, url = {http://users.neurostat.mit.edu/lciti/publications_files/Pani2016RealTimeNeuralSignals.pdf} }  @article{Poli2010ReactionTimeBinningForIncrResolvPowerERPAverages, title = {Reaction-time binning: a simple method for increasing the resolving power of ERP averages.}, author = {Riccardo Poli and Caterina Cinel and Luca Citi and Francisco Sepulveda}, journal = {Psychophysiology}, year = {2010}, month = may, number = {3}, pages = {467--485}, volume = {47}, abstract = {Stimulus-locked, response-locked, and ERP-locked averaging are effective methods for reducing artifacts in ERP analysis. However, they suffer from a magnifying-glass effect: they increase the resolution of specific ERPs at the cost of blurring other ERPs. Here we propose an extremely simple technique-binning trials based on response times and then averaging-which can significantly alleviate the problems of other averaging methods. We have empirically evaluated the technique in an experiment where the task requires detecting a target in the presence of distractors. We have also studied the signal-to-noise ratio and the resolving power of averages with and without binning. Results indicate that the method produces clearer representations of ERPs than either stimulus-locked and response-locked averaging, revealing finer details of ERPs and helping in the evaluation of the amplitude and latency of ERP waves. The method is applicable to within-subject and between-subject averages.}, check = {2011.08.17}, doi = {10.1111/j.1469-8986.2009.00959.x}, institution = {Brain Computer Interfaces Laboratory, School of Computer Science and Electronic Engineering, University of Essex, Colchester, 304 ESQ, UK. rpoli@essex.ac.uk}, keywords = {Adult; Algorithms; Artifacts; Data Interpretation, Statistical; Electroencephalography, statistics /&/ numerical data; Evoked Potentials, physiology; Female; Humans; Male; Models, Statistical; Photic Stimulation; Psychomotor Performance, physiology; Reaction Time, physiology; Sample Size; Young Adult}, language = {eng}, medline-pst = {ppublish}, owner = {lciti}, pii = {PSYP959}, pmid = {20070576}, timestamp = {2010.10.27}, url = {http://users.neurostat.mit.edu/lciti/publications_files/Poli2010ReactionTimeBinningForIncrResolvPowerERPAverages.pdf} }  @article{Poli2009AnalogueEvolutionaryBCI, title = {Analogue evolutionary brain computer interfaces}, author = {Poli, Riccardo and Citi, Luca and Sepulveda, Francisco and Cinel, Caterina}, journal = {IEEE Computational Intelligence Magazine}, year = {2009}, month = nov, number = {4}, pages = {27 -31}, volume = {4}, abstract = {The keyboard is a device that, provides an interface that is reliable but also very unnatural. The mouse is only slightly less primitive, being an electro-mechanical transducer of musculoskeletal movement. Both have been with us for decades, yet they are unusable for people with severe musculoskeletal disorders and are themselves known causes of work-related upper-limb and back disorders, both hugely widespread problems. It will be a major contribution to computer interface technology to replace mouse and keyboard with brain-computer interfaces (BCIs) capable of directly interpreting the desires and intentions of computer users. In this article we describe the approach, results and promising new research directions in the realization of BCIs, with particular reference to a 2D pointing device. Three features characterize the approach. Firstly, BCI is logically analogue, second is the use of evolutionary algorithms, and the third feature is its interdisciplinarity.}, check = {2010.10.27}, doi = {10.1109/MCI.2009.934563}, issn = {1556-603X}, keywords = {2D pointing device;BCI approach;back disorders;brain computer interfaces;evolutionary algorithms;logically analogue system;musculoskeletal disorders;work-related upper-limb disorder;brain-computer interfaces;evolutionary computation;human computer interaction;}, owner = {lciti}, timestamp = {2010.10.27} }  @article{Poli2009MemoryWithMemoryGP, title = {Memory with memory in genetic programming}, author = {Poli, Riccardo and McPhee, Nicholas Freitag and Citi, Luca and Crane, Ellery}, journal = {Journal of Artificial Evolution and Applications}, year = {2009}, month = jan, pages = {1--16}, volume = {2009}, abstract = {We introduce Memory with Memory Genetic Programming (MwM-GP), where we use soft assignments and soft return operations. Instead of having the new value completely overwrite the old value of registers or memory, soft assignments combine such values. Similarly, in soft return operations the value of a function node is a blend between the result of a calculation and previously returned results. In extensive empirical tests, MwM-GP almost always does as well as traditional GP, while significantly outperforming it in several cases. MwM-GP also tends to be far more consistent than traditional GP. The data suggest that MwM-GP works by successively refining an approximate solution to the target problem and that it is much less likely to have truly ineffective code. MwM-GP can continue to improve over time, but it is less likely to get the sort of exact solution that one might find with traditional GP.}, check = {2010.10.28}, doi = {10.1155/2009/570606}, issn = {1687-6229}, owner = {lciti}, timestamp = {2010.10.28} }  @article{raspopovic2014restoring, title = {Restoring natural sensory feedback in real-time bidirectional hand prostheses}, author = {Raspopovic, Stanisa and Capogrosso, Marco and Petrini, Francesco Maria and Bonizzato, Marco and Rigosa, Jacopo and Di Pino, Giovanni and Carpaneto, Jacopo and Controzzi, Marco and Boretius, Tim and Fernandez, Eduardo and others}, journal = {Science translational medicine}, year = {2014}, month = feb, number = {222}, pages = {222ra19}, volume = {6}, abstract = {Hand loss is a highly disabling event that markedly affects the quality of life. To achieve a close to natural replacement for the lost hand, the user should be provided with the rich sensations that we naturally perceive when grasping or manipulating an object. Ideal bidirectional hand prostheses should involve both a reliable decoding of the user's intentions and the delivery of nearly "natural" sensory feedback through remnant afferent pathways, simultaneously and in real time. However, current hand prostheses fail to achieve these requirements, particularly because they lack any sensory feedback. We show that by stimulating the median and ulnar nerve fascicles using transversal multichannel intrafascicular electrodes, according to the information provided by the artificial sensors from a hand prosthesis, physiologically appropriate (near-natural) sensory information can be provided to an amputee during the real-time decoding of different grasping tasks to control a dexterous hand prosthesis. This feedback enabled the participant to effectively modulate the grasping force of the prosthesis with no visual or auditory feedback. Three different force levels were distinguished and consistently used by the subject. The results also demonstrate that a high complexity of perception can be obtained, allowing the subject to identify the stiffness and shape of three different objects by exploiting different characteristics of the elicited sensations. This approach could improve the efficacy and "life-like" quality of hand prostheses, resulting in a keystone strategy for the near-natural replacement of missing hands.}, check = {2015.01.22}, doi = {10.1126/scitranslmed.3006820}, owner = {lciti}, timestamp = {2015.01.22} }  @article{Rossini2010DoubleNerveIntranInterfHumanAmputee, title = {Double nerve intraneural interface implant on a human amputee for robotic hand control.}, author = {Paolo M Rossini and Silvestro Micera and Antonella Benvenuto and Jacopo Carpaneto and Giuseppe Cavallo and Luca Citi and Christian Cipriani and Luca Denaro and Vincenzo Denaro and Giovanni Di Pino and Florinda Ferreri and Eugenio Guglielmelli and Klaus-Peter Hoffmann and Stanisa Raspopovic and Jacopo Rigosa and Luca Rossini and Mario Tombini and Paolo Dario}, journal = {Clinical Neurophysiology}, year = {2010}, month = may, number = {5}, pages = {777--783}, volume = {121}, abstract = {OBJECTIVES: The principle underlying this project is that, despite nervous reorganization following upper limb amputation, original pathways and CNS relays partially maintain their function and can be exploited for interfacing prostheses. Aim of this study is to evaluate a novel peripheral intraneural multielectrode for multi-movement prosthesis control and for sensory feed-back, while assessing cortical reorganization following the re-acquired stream of data. METHODS: Four intrafascicular longitudinal flexible multielectrodes (tf-LIFE4) were implanted in the median and ulnar nerves of an amputee; they reliably recorded output signals for 4 weeks. Artificial intelligence classifiers were used off-line to analyse LIFE signals recorded during three distinct hand movements under voluntary order. RESULTS: Real-time control of motor output was achieved for the three actions. When applied off-line artificial intelligence reached >85\% real-time correct classification of trials. Moreover, different types of current stimulation were determined to allow reproducible and localized hand/fingers sensations. Cortical organization was observed via TMS in parallel with partial resolution of symptoms due to the phantom-limb syndrome (PLS). CONCLUSIONS: tf-LIFE4s recorded output signals in human nerves for 4 weeks, though the efficacy of sensory stimulation decayed after 10 days. Recording from a number of fibres permitted a high percentage of distinct actions to be classified correctly. Reversal of plastic changes and alleviation of PLS represent corollary findings of potential therapeutic benefit. SIGNIFICANCE: This study represents a breakthrough in robotic hand use in amputees.}, check = {2011.01.12}, doi = {10.1016/j.clinph.2010.01.001}, institution = {Dept. of Neurology, University Campus Bio-Medico, Rome, Italy. p.rossini@unicampus.it}, keywords = {Adult; Amputation, Traumatic, complications; Amputees; Artificial Limbs; Computer Systems; Electric Stimulation; Electrodes, Implanted; Hand; Humans; Internal-External Control; Male; Median Nerve, physiopathology/surgery; Movement; Nerve Fibers; Neuronal Plasticity; Phantom Limb, etiology/physiopathology/surgery; Robotics; Sensation; Transcranial Magnetic Stimulation; Ulnar Nerve, physiopathology/surgery}, language = {eng}, medline-pst = {ppublish}, owner = {lciti}, pii = {S1388-2457(10)00003-9}, pmid = {20110193}, timestamp = {2010.10.27}, url = {http://users.neurostat.mit.edu/lciti/publications_files/Rossini2010DoubleNerveIntranInterfHumanAmputee.pdf} }  @article{Salvaris2012NovelProtocolsP300BCI, title = {Novel Protocols for {P300}-Based Brain-Computer Interfaces}, author = {Salvaris, Mathew and Cinel, Caterina and Citi, Luca and Poli, Riccardo}, journal = {IEEE Transactions on Neural System and Rehabilitation Engineering}, year = {2012}, month = jan, number = {1}, pages = {8--17}, volume = {20}, abstract = {The oddball protocol is often used in Brain- Computer Interfaces (BCIs) to induce P300 ERPs, although, recently, some issues have been shown to detrimentally effect its performance. In this paper, we study a new periodic protocol and explore whether it can compete with the standard oddball protocol within the context of a BCI mouse. We found that the new protocol consistently and significantly outperforms the standard oddball protocol in relation to information transfer rates (33 bits/min for the former and 22 bits/min for the latter, measured at 90% accuracy) as well as P300 amplitudes. Furthermore, we performed a comparison of two periodic protocols with two less conventional oddball-like protocols that reveals the importance of the interactions between task and sequence in determining the success of a protocol.}, check = {2012.09.26}, doi = {10.1109/TNSRE.2011.2174463}, owner = {lciti}, timestamp = {2012.01.10}, url = {http://users.neurostat.mit.edu/lciti/publications_files/Salvaris2012NovelProtocolsP300BCI.pdf} }  @article{Tombini2011CombinedAnalysisEEGENGRoboticHand, title = {Combined Analysis of Cortical ({EEG}) and Nerve Stump Signals Improves Robotic Hand Control.}, author = {Mario Tombini and Jacopo Rigosa and Filippo Zappasodi and Camillo Porcaro and Luca Citi and Jacopo Carpaneto and Paolo Maria Rossini and Silvestro Micera}, journal = {Neurorehabil Neural Repair}, year = {2012}, month = jul, pages = {275--281}, volume = {26}, abstract = {BACKGROUND: Interfacing an amputee's upper-extremity stump nerves to control a robotic hand requires training of the individual and algorithms to process interactions between cortical and peripheral signals. OBJECTIVE: To evaluate for the first time whether EEG-driven analysis of peripheral neural signals as an amputee practices could improve the classification of motor commands. METHODS: Four thin-film longitudinal intrafascicular electrodes (tf-LIFEs-4) were implanted in the median and ulnar nerves of the stump in the distal upper arm for 4 weeks. Artificial intelligence classifiers were implemented to analyze LIFE signals recorded while the participant tried to perform 3 different hand and finger movements as pictures representing these tasks were randomly presented on a screen. In the final week, the participant was trained to perform the same movements with a robotic hand prosthesis through modulation of tf-LIFE-4 signals. To improve the classification performance, an event-related desynchronization/synchronization (ERD/ERS) procedure was applied to EEG data to identify the exact timing of each motor command. RESULTS: Real-time control of neural (motor) output was achieved by the participant. By focusing electroneurographic (ENG) signal analysis in an EEG-driven time window, movement classification performance improved. After training, the participant regained normal modulation of background rhythms for movement preparation (\alpha/\beta band desynchronization) in the sensorimotor area contralateral to the missing limb. Moreover, coherence analysis found a restored \alpha band synchronization of Rolandic area with frontal and parietal ipsilateral regions, similar to that observed in the opposite hemisphere for movement of the intact hand. Of note, phantom limb pain (PLP) resolved for several months. CONCLUSIONS: Combining information from both cortical (EEG) and stump nerve (ENG) signals improved the classification performance compared with tf-LIFE signals processing alone; training led to cortical reorganization and mitigation of PLP.}, check = {2012.09.26}, doi = {10.1177/1545968311408919}, owner = {lciti}, pii = {1545968311408919}, pmid = {21730360}, timestamp = {2011.09.07} }  @article{Tonet2008DefBMIApplicMergingIntPerfDevicRequir, title = {Defining {Brain-Machine Interface} applications by matching interface performance with device requirements.}, author = {Oliver Tonet and Martina Marinelli and Luca Citi and Paolo Maria Rossini and Luca Rossini and Giuseppe Megali and Paolo Dario}, journal = {Journal of Neuroscience Methods}, year = {2008}, month = jan, number = {1}, pages = {91--104}, volume = {167}, abstract = {Interaction with machines is mediated by human-machine interfaces (HMIs). Brain-machine interfaces (BMIs) are a particular class of HMIs and have so far been studied as a communication means for people who have little or no voluntary control of muscle activity. In this context, low-performing interfaces can be considered as prosthetic applications. On the other hand, for able-bodied users, a BMI would only be practical if conceived as an augmenting interface. In this paper, a method is introduced for pointing out effective combinations of interfaces and devices for creating real-world applications. First, devices for domotics, rehabilitation and assistive robotics, and their requirements, in terms of throughput and latency, are described. Second, HMIs are classified and their performance described, still in terms of throughput and latency. Then device requirements are matched with performance of available interfaces. Simple rehabilitation and domotics devices can be easily controlled by means of BMI technology. Prosthetic hands and wheelchairs are suitable applications but do not attain optimal interactivity. Regarding humanoid robotics, the head and the trunk can be controlled by means of BMIs, while other parts require too much throughput. Robotic arms, which have been controlled by means of cortical invasive interfaces in animal studies, could be the next frontier for non-invasive BMIs. Combining smart controllers with BMIs could improve interactivity and boost BMI applications.}, check = {2011.08.17}, doi = {10.1016/j.jneumeth.2007.03.015}, institution = {CRIM Lab, Scuola Superiore Sant'Anna, Pisa, Italy. oliver.tonet@sssup.it}, keywords = {Brain; Communication Aids for Disabled; Computer Simulation; Electroencephalography; Feedback; Humans; Man-Machine Systems; Numerical Analysis, Computer-Assisted; Reaction Time; User-Computer Interface}, owner = {lciti}, pii = {S0165-0270(07)00143-4}, pmid = {17499364}, timestamp = {2008.09.07}, url = {http://users.neurostat.mit.edu/lciti/publications_files/Tonet2008DefBMIApplicMergingIntPerfDevicRequir.pdf} }  @article{valenza2014instantaneous, title = {Instantaneous monitoring of heart beat dynamics during anesthesia and sedation}, author = {Valenza, Gaetano and Akeju, Oluwaseun and Pavone, Kara J and Citi, Luca and Hartnack, Katharine E and Sampson, Aaron and Purdon, Patrick L and Brown, Emery N and Barbieri, Riccardo}, journal = {Journal of Computational Surgery}, year = {2014}, number = {1}, pages = {1--18}, volume = {3}, doi = {10.1186/s40244-014-0013-2}, owner = {lciti}, timestamp = {2015.01.22} }  @article{valenza2014estimation, title = {Estimation of instantaneous complex dynamics through Lyapunov exponents: a study on heartbeat dynamics}, author = {Valenza, Gaetano and Citi, Luca and Barbieri, Riccardo}, journal = {PloS one}, year = {2014}, number = {8}, pages = {e105622}, volume = {9}, doi = {10.1371/journal.pone.0105622}, owner = {lciti}, publisher = {Public Library of Science}, timestamp = {2015.01.22} }  @article{Valenza2017ComplexityVariabilityAssessment, title = {Complexity Variability Assessment of Nonlinear Time-Varying Cardiovascular Control}, author = {Gaetano Valenza and Luca Citi and Ronald G Garcia and Jessica Noggle Taylor and Nicola Toschi and Riccardo Barbieri}, journal = {Scientific Reports}, year = {2017}, month = feb, pages = {42779}, volume = {7}, abstract = {The application of complex systems theory to physiology and medicine has provided meaningful information about the nonlinear aspects underlying the dynamics of a wide range of biological processes and their disease-related aberrations. However, no studies have investigated whether meaningful information can be extracted by quantifying second-order moments of time-varying cardiovascular complexity. To this extent, we introduce a novel mathematical framework termed complexity variability, in which the variance of instantaneous Lyapunov spectra estimated over time serves as a reference quantifier. We apply the proposed methodology to four exemplary studies involving disorders which stem from cardiology, neurology and psychiatry: Congestive Heart Failure (CHF), Major Depression Disorder (MDD), Parkinson?s Disease (PD), and Post-Traumatic Stress Disorder (PTSD) patients with insomnia under a yoga training regime. We show that complexity assessments derived from simple time-averaging are not able to discern pathology-related changes in autonomic control, and we demonstrate that between-group differences in measures of complexity variability are consistent across pathologies. Pathological states such as CHF, MDD, and PD are associated with an increased complexity variability when compared to healthy controls, whereas wellbeing derived from yoga in PTSD is associated with lower time-variance of complexity.}, doi = {10.1038/srep42779}, owner = {lciti}, publisher = {Nature Publishing Group}, timestamp = {2017.06.02} }  @article{Valenza2014PPNonlinAutonAssessDepressStates, title = {Point-process Nonlinear Autonomic Assessment of Depressive States in Bipolar Patients}, author = {G Valenza and Luca Citi and C Gentili and A Lanat{\'a} and E P Scilingo and R Barbieri}, journal = {Methods of Information in Medicine}, year = {2014}, number = {4}, pages = {296--302}, volume = {53}, abstract = {Introduction: This article is part of the Focus Theme of Methods of Information in Medicine on "Biosignal Interpretation: Advanced Methods for Studying Cardiovascular and Respiratory Systems". Objectives: The goal of this work is to apply a computational methodology able to characterize mood states in bipolar patients through instantaneous analysis of heartbeat dynamics. Methods: A Point-Process-based Nonlinear Autoregressive Integrative (NARI) model is applied to analyze data collected from five bipolar patients (two males and three females, age 42.4 {$\pm$} 10.5 range 32--56) undergoing a dedicated affective elicitation protocol using images from the International Affective Picture System (IAPS) and Thematic Apperception Test (TAT). The study was designed within the European project PSYCHE (Personalised monitoring SYstems for Care in mental HEalth). Results: Results demonstrate that the inclusion of instantaneous higher order spectral (HOS) features estimated from the NARI nonlinear assessment significantly improves the accuracy in successfully recognizing specific mood states such as euthymia and depression with respect to results using only linear indices. In particular, a specificity of 74.44\% using the instantaneous linear features set, and 99.56\% using also the nonlinear feature set were achieved. Moreover, IAPS emotional elicitation resulted in a more discriminant procedure with respect to the TAT elicitation protocol. Conclusions: A significant pattern of instantaneous heartbeat features was found in depressive and euthymic states despite the inter-subject variability. The presented point-process Heart Rate Variability (HRV) nonlinear methodology provides a promising application in the field of mood assessment in bipolar patients.}, keywords = {bipolar disorder, Heart Rate Variability (HRV), Point Process, High Order Statistics, Bispectrum, Nonlinear Analysis, Wiener-Volterra Series, International Affective Picture System (IAPS), Thematic Apperception Test (TAT)}, owner = {lciti}, publisher = {Schattauer}, timestamp = {2016.01.06} }  @article{Valenza2015CharDepressStatesBipolar, title = {Characterization of depressive States in bipolar patients using wearable textile technology and instantaneous heart rate variability assessment}, author = {Valenza, Gaetano and Citi, Luca and Gentili, Claudio and Lanata, Antonio and Scilingo, Enzo Pasquale and Barbieri, Riccardo}, journal = {IEEE Journal of Biomedical and Health Informatics}, year = {2015}, month = jan, number = {1}, pages = {263--274}, volume = {19}, abstract = {The analysis of cognitive and autonomic responses to emotionally relevant stimuli could provide a viable solution for the automatic recognition of different mood states, both in normal and pathological conditions. In this study, we present a methodological application describing a novel system based on wearable textile technology and instantaneous nonlinear heart rate variability assessment, able to characterize the autonomic status of bipolar patients by considering only electrocardiogram recordings. As a proof of this concept, our study presents results obtained from eight bipolar patients during their normal daily activities and being elicited according to a specific emotional protocol through the presentation of emotionally relevant pictures. Linear and nonlinear features were computed using a novel point-process-based nonlinear autoregressive integrative model and compared with traditional algorithmic methods. The estimated indices were used as the input of a multilayer perceptron to discriminate the depressive from the euthymic status. Results show that our system achieves much higher accuracy than the traditional techniques. Moreover, the inclusion of instantaneous higher order spectra features significantly improves the accuracy in successfully recognizing depression from euthymia.}, doi = {10.1109/JBHI.2014.2307584}, owner = {lciti}, pmid = {25561449}, timestamp = {2015.06.07} }  @article{Valenza2014RevelRealTimeEmotionalResp, title = {Revealing Real-Time Emotional Responses: a Personalized Assessment based on Heartbeat Dynamics}, author = {Valenza, Gaetano and Citi, Luca and Lanat{\'a}, Antonio and Scilingo, Enzo Pasquale and Barbieri, Riccardo}, journal = {Scientific Reports}, year = {2014}, month = may, volume = {4}, abstract = {Emotion recognition through computational modeling and analysis of physiological signals has been widely investigated in the last decade. Most of the proposed emotion recognition systems require relatively long-time series of multivariate records and do not provide accurate real-time characterizations using short-time series. To overcome these limitations, we propose a novel personalized probabilistic framework able to characterize the emotional state of a subject through the analysis of heartbeat dynamics exclusively. The study includes thirty subjects presented with a set of standardized images gathered from the international affective picture system, alternating levels of arousal and valence. Due to the intrinsic nonlinearity and nonstationarity of the {RR} interval series, a specific point-process model was devised for instantaneous identification considering autoregressive nonlinearities up to the third-order according to the Wiener-Volterra representation, thus tracking very fast stimulus-response changes. Features from the instantaneous spectrum and bispectrum, as well as the dominant Lyapunov exponent, were extracted and considered as input features to a support vector machine for classification. Results, estimating emotions each 10 seconds, achieve an overall accuracy in recognizing four emotional states based on the circumplex model of affect of 79.29\%, with 79.15\% on the valence axis, and 83.55\% on the arousal axis.}, check = {2015.01.22}, doi = {10.1038/srep04998}, keywords = {Applied mathematics, Biomedical engineering, Computational biophysics, Computational science}, owner = {lciti}, publisher = {Nature Publishing Group}, shorttitle = {Revealing Real-Time Emotional Responses}, timestamp = {2015.01.22} }  @article{Valenza2014InhomPPEntropy, title = {Inhomogeneous point-process entropy: an instantaneous measure of complexity in discrete systems}, author = {Valenza, Gaetano and Citi, Luca and Scilingo, Enzo Pasquale and Barbieri, Riccardo}, journal = {Physical Review E}, year = {2014}, month = may, number = {5}, pages = {052803}, volume = {89}, abstract = {Measures of entropy have been widely used to characterize complexity, particularly in physiological dynamical systems modeled in discrete time. Current approaches associate these measures to finite single values within an observation window, thus not being able to characterize the system evolution at each moment in time. Here, we propose a new definition of approximate and sample entropy based on the inhomogeneous point-process theory. The discrete time series is modeled through probability density functions, which characterize and predict the time until the next event occurs as a function of the past history. Laguerre expansions of the Wiener-Volterra autoregressive terms account for the long-term nonlinear information. As the proposed measures of entropy are instantaneously defined through probability functions, the novel indices are able to provide instantaneous tracking of the system complexity. The new measures are tested on synthetic data, as well as on real data gathered from heartbeat dynamics of healthy subjects and patients with cardiac heart failure and gait recordings from short walks of young and elderly subjects. Results show that instantaneous complexity is able to effectively track the system dynamics and is not affected by statistical noise properties.}, check = {2015.01.22}, doi = {10.1103/PhysRevE.89.052803}, owner = {lciti}, publisher = {American Physical Society}, timestamp = {2015.01.22}, url = {http://dspace.mit.edu/openaccess-disseminate/1721.1/88657} }  @article{ValenzaCiti2013PointProcNonlinLaguerre, title = {Point-Process Nonlinear Models with {L}aguerre and {V}olterra Expansions: Instantaneous Assessment of Heartbeat Dynamics}, author = {Valenza, Gaetano and Citi, Luca and Scilingo, Enzo Pasquale and Barbieri, Riccardo}, journal = {IEEE Transactions on Signal Processing}, year = {2013}, month = jun, number = {11}, pages = {2914--2926}, volume = {61}, abstract = {In the last decades, mathematical modelling and signal processing techniques have played an important role in the study of cardiovascular control physiology and heartbeat nonlinear dynamics. In particular, nonlinear models have been devised for the assessment of the cardiovascular system by accounting for short-memory second-order nonlinearities. In this paper, we introduce a novel inverse Gaussian point process model with Laguerre expansion of the nonlinear Volterra kernels. Within the model, the second-order nonlinearities also account for the long-term information given by the past events of the nonstationary non-Gaussian time series. In addition, the mathematical link to an equivalent cubic input-output Wiener-Volterra model allows for a novel instantaneous estimation of the dynamic spectrum, bispectrum and trispectrum of the considered inter-event intervals. The proposed framework is tested with synthetic simulations and two experimental heartbeat interval datasets. Applications on further heterogeneous datasets such as milling inserts, neural spikes, gait from short walks, and geyser geologic events are also reported. Results show that our model improves on previously developed models and, at the same time, it is able to provide a novel instantaneous characterization and tracking of the inherent nonlinearity of heartbeat dynamics.}, check = {2014.01.23}, doi = {10.1109/TSP.2013.2253775}, owner = {lciti}, publisher = {IEEE}, timestamp = {2015.01.23} }  @article{Valenza2015NonlinearDigSigProcMentalHealth, title = {Nonlinear digital signal processing in mental health: characterization of major depression using instantaneous entropy measures of heartbeat dynamics}, author = {Valenza, Gaetano and Garcia, Ronald G. and Citi, Luca and Scilingo, Enzo P. and Tomaz, Carlos A. and Barbieri, Riccardo}, journal = {Frontiers in Physiology}, year = {2015}, month = mar, pages = {74}, volume = {6}, abstract = {Nonlinear digital signal processing methods that address system complexity have provided useful computational tools for helping in the diagnosis and treatment of a wide range of pathologies. More specifically, nonlinear measures have been successful in characterizing patients with mental disorders such as Major Depression (MD). In this study, we propose the use of instantaneous measures of entropy, namely the inhomogeneous point-process approximate entropy (ipApEn) and the inhomogeneous point-process sample entropy (ipSampEn), to describe a novel characterization of MD patients undergoing affective elicitation. Because these measures are built within a nonlinear point-process model, they allow for the assessment of complexity in cardiovascular dynamics at each moment in time. Heartbeat dynamics were characterized from 48 healthy controls and 48 patients with MD while emotionally elicited through either neutral or arousing audiovisual stimuli. Experimental results coming from the arousing tasks show that ipApEn measures are able to instantaneously track heartbeat complexity as well as discern between healthy subjects and MD patients. Conversely, standard heart rate variability (HRV) analysis performed in both time and frequency domains did not show any statistical significance. We conclude that measures of entropy based on nonlinear point-process models might contribute to devising useful computational tools for care in mental health.}, doi = {10.3389/fphys.2015.00074}, owner = {lciti}, pmid = {25821435}, timestamp = {2015.06.07} }  @article{Valenza2016InhomogeneousPoint-Processes, title = {Inhomogeneous Point-Processes to Instantaneously Assess Affective Haptic Perception through Heartbeat Dynamics Information}, author = {{Valenza}, G. and {Greco}, A. and {Citi}, L. and {Bianchi}, M. and {Barbieri}, R. and {Scilingo}, E.~P.}, journal = {Scientific Reports}, year = {2016}, month = jun, pages = {28567}, volume = {6}, abstract = {This study proposes the application of a comprehensive signal processing framework, based on inhomogeneous point-process models of heartbeat dynamics, to instantaneously assess affective haptic perception using electrocardiogram-derived information exclusively. The framework relies on inverse-Gaussian point-processes with Laguerre expansion of the nonlinear Wiener-Volterra kernels, accounting for the long-term information given by the past heartbeat events. Up to cubic-order nonlinearities allow for an instantaneous estimation of the dynamic spectrum and bispectrum of the considered cardiovascular dynamics, as well as for instantaneous measures of complexity, through Lyapunov exponents and entropy. Short-term caress-like stimuli were administered for 4.3-25 seconds on the forearms of 32 healthy volunteers (16 females) through a wearable haptic device, by selectively superimposing two levels of force, 2 N and 6 N, and two levels of velocity, 9.4 mm/s and 65 mm/s. Results demonstrated that our instantaneous linear and nonlinear features were able to finely characterize the affective haptic perception, with a recognition accuracy of 69.79% along the force dimension, and 81.25% along the velocity dimension.}, doi = {10.1038/srep28567}, eid = {28567}, owner = {lciti}, timestamp = {2017.06.02} }  @article{Valenza2016AssessmentSpontanuousCardiovOscParkinsons, title = {Assessment of spontaneous cardiovascular oscillations in Parkinson's disease}, author = {Valenza, Gaetano and Orsolini, Stefano and Diciotti, Stefano and Citi, Luca and Scilingo, Enzo Pasquale and Guerrisi, Maria and Danti, Sabrina and Lucetti, Claudio and Tessa, Carlo and Barbieri, Riccardo and others}, journal = {Biomedical Signal Processing and Control}, year = {2016}, month = apr, pages = {80--89}, volume = {26}, abstract = {Parkinson's disease (PD) has been reported to involve postganglionic sympathetic failure and a wide spectrum of autonomic dysfunctions including cardiovascular, sexual, bladder, gastrointestinal and sudo-motor abnormalities. While these symptoms may have a significant impact on daily activities, as well as quality of life, the evaluation of autonomic nervous system (ANS) dysfunctions relies on a large and expensive battery of autonomic tests only accessible in highly specialized laboratories. In this paper we aim to devise a comprehensive computational assessment of disease-related heartbeat dynamics based on instantaneous, time-varying estimates of spontaneous (resting state) cardiovascular oscillations in PD. To this end, we combine standard ANS-related heart rate variability (HRV) metrics with measures of instantaneous complexity (dominant Lyapunov exponent and entropy) and higher-order statistics (bispectra). Such measures are computed over 600-s recordings acquired at rest in 29 healthy subjects and 30 PD patients. The only significant group-wise differences were found in the variability of the dominant Lyapunov exponent. Also, the best PD vs. healthy controls classification performance (balanced accuracy: 73.47%) was achieved only when retaining the time-varying, non-stationary structure of the dynamical features, whereas classification performance dropped significantly (balanced accuracy: 61.91%) when excluding variability-related features. Additionally, both linear and nonlinear model features correlated with both clinical and neuropsychological assessments of the considered patient population. Our results demonstrate the added value and potential of instantaneous measures of heartbeat dynamics and its variability in characterizing PD-related disabilities in motor and cognitive domains.}, doi = {10.1016/j.bspc.2015.12.001}, owner = {lciti}, publisher = {Elsevier} }  @article{Valenza20181077, author = {Valenza, G. and Faes, L. and Citi, L. and Orini, M. and Barbieri, R.}, title = {Instantaneous Transfer Entropy for the Study of Cardiovascular and Cardiorespiratory Nonstationary Dynamics}, journal = {IEEE Transactions on Biomedical Engineering}, year = {2018}, volume = {65}, number = {5}, pages = {1077-1085}, abstract = {Objective: Measures of transfer entropy (TE) quantify the direction and strength of coupling between two complex systems. Standard approaches assume stationarity of the observations, and therefore are unable to track time-varying changes in nonlinear information transfer with high temporal resolution. In this study, we aim to define and validate novel instantaneous measures of TE to provide an improved assessment of complex nonstationary cardiorespiratory interactions. Methods: We here propose a novel instantaneous point-process TE (ipTE) and validate its assessment as applied to cardiovascular and cardiorespiratory dynamics. In particular, heartbeat and respiratory dynamics are characterized through discrete time series, and modeled with probability density functions predicting the time of the next physiological event as a function of the past history. Likewise, nonstationary interactions between heartbeat and blood pressure dynamics are characterized as well. Furthermore, we propose a new measure of information transfer, the instantaneous point-process information transfer (ipInfTr), which is directly derived from point-process-based definitions of the Kolmogorov-Smirnov distance. Results and Conclusion: Analysis on synthetic data, as well as on experimental data gathered from healthy subjects undergoing postural changes confirms that ipTE, as well as ipInfTr measures are able to dynamically track changes in physiological systems coupling. Significance: This novel approach opens new avenues in the study of hidden, transient, nonstationary physiological states involving multivariate autonomic dynamics in cardiovascular health and disease. The proposed method can also be tailored for the study of complex multisystem physiology (e.g., brain-heart or, more in general, brain-body interactions). © 1964-2012 IEEE.}, doi = {10.1109/TBME.2017.2740259} }  @comment{{jabref-meta: databaseType:bibtex;}}  @incollection{Citi2013WavDenNeuralSignals, title = {Wavelet denoising and conditioning of neural recordings}, author = {Luca Citi and Silvestro Micera}, booktitle = {Introduction to Neural Engineering for Motor Rehabilitation}, publisher = {IEEE/Wiley Press}, year = {2013}, chapter = {9}, editor = {Dario Farina and Winnie Jensen and Metin Akay}, check = {2012.12.13}, owner = {lciti}, timestamp = {2012.12.13} }  @incollection{Citi2010HighSignifAveragesERPViaGP, title = {High-Significance Averages of Event-Related Potential Via Genetic Programming}, author = {Citi, Luca and Poli, Riccardo and Cinel, Caterina}, booktitle = {Genetic Programming Theory and Practice VII}, publisher = {Springer US}, year = {2010}, chapter = {9}, editor = {Riolo, Rick and O'Reilly, Una-May and McConaghy, Trent}, pages = {135-157}, series = {Genetic and Evolutionary Computation}, abstract = {In this paper we use register-based genetic programming with memory-with memory to discover probabilistic membership functions that are used to divide up data-sets of event-related potentials recorded via EEG in psycho-physiological experiments based on the corresponding response times. The objective is to evolve membership functions which lead to maximising the statistical significance with which true brain waves can be reconstructed when averaging the trials in each bin. Results show that GP can significantly improve the fidelity with which ERP components can be recovered.}, affiliation = {University of Essex School of Computer Science and Electronic Engineering Wivenhoe Park CO4 3SQ UK}, check = {2010.10.28}, doi = {10.1007/978-1-4419-1626-6_9}, isbn = {978-1-4419-1626-6}, keyword = {Computer Science}, owner = {lciti}, timestamp = {2010.10.28} }  @incollection{Carpaneto2013311, author = {Carpaneto, J. and Citi, L. and Raspopovic, S. and Rigosa, J. and Micera, S.}, title = {Controlling Prostheses Using PNS Invasive Interfaces for Amputees}, booktitle = {Introduction to Neural Engineering for Motor Rehabilitation}, publisher = {IEEE/Wiley Press}, year = {2013}, pages = {311-326}, abstract = {Several attempts have been made to enhance the control of highly sensorized prostheses. One of the main goals is to create a bidirectional link between the prosthesis and the nervous system. Several approaches based on noninvasive and invasive interfaces have been developed and tested. Among these, interfaces with the peripheral nervous system (PNS), especially longitudinal intrafascicular electrodes (LIFEs), seem to be a promising solution. This chapter presents the potential and the limits of these interfaces for the control of prosthetic devices. It reviews the state of the art of artificial hand control based on the use of invasive interfaces with the PNS. Decoding algorithms represent a critical step for electroneurographic (ENG)-based hand prosthesis control. Algorithms have been mainly developed for the closed-loop control of functional electrical stimulation (FES) systems. Several techniques have been developed to provide noninvasive tactile or proprioceptive information to the amputees. © 2013 The Institute of Electrical and Electronics Engineers, Inc. All rights reserved.}, doi = {10.1002/9781118628522.ch16} }  @incollection{Valenza2017345, author = {Valenza, G. and Citi, L. and Lanata, A. and Gentili, C. and Barbieri, R. and Scilingo, E.P.}, title = {Applications of heartbeat complexity analysis to depression and bipolar disorder}, booktitle = {Complexity and Nonlinearity in Cardiovascular Signals}, publisher = {Springer}, year = {2017}, pages = {345-374}, abstract = {Nonlinear digital signal processing methods addressing system complexity have provided useful computational tools for helping in the diagnosis and treatment monitoring of a wide range of pathologies. In particular, heartbeat complexity measures have been successful in characterizing patients with mental disorders such as Major Depression and Bipolar Disorder. In this chapter, we describe the use of standard complexity measures such as sample entropy and multiscale entropy, as well as instantaneous measures of entropy to characterize pathological mood states when patients undergo affective elicitation or longterm monitoring. Results demonstrate that complexity measures of cardiovascular dynamics can be promising and viable tools to support clinical decision in mental health, improving on the diagnosis and management of psychiatric disorders. © 2017, Springer International Publishing AG.}, document_type = {Book Chapter}, doi = {10.1007/978-3-319-58709-7_13}, journal = {Complexity and Nonlinearity in Cardiovascular Signals}, url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85037157455&doi=10.1007%2f978-3-319-58709-7_13&partnerID=40&md5=33987884cb93f5b1e95b45eaa71b89e6} }  @incollection{Valenza2017233, author = {Valenza, G. and Citi, L. and Scilingo, E.P. and Barbieri, R.}, title = {Time-varying cardiovascular complexity with focus on entropy and lyapunov exponents}, booktitle = {Complexity and Nonlinearity in Cardiovascular Signals}, publisher = {Springer}, year = {2017}, pages = {233-256}, abstract = {Measures of nonlinearity and complexity, such as entropy measures and Lyapunov exponents, have been increasingly employed to characterize dynamical properties in a wide range of biological nonlinear systems, including cardiovascular control. In this chapter, we present recent methodological advances allowing to effectively estimate instantaneous approximate and sample entropy measures, as well as the instantaneous Lyapunov spectrum of a series of stochastic events, i.e., the heartbeats. Because the proposed measures are instantaneously defined by means of probability functions defined within a point-process framework, these indices are able to provide instantaneous tracking of the degree of complexity associated with the physiological system in question. Long-term information is taken into account by expanding the linear, quadratic, and cubic Wiener-Volterra kernels with the orthonormal Laguerre basis functions. Applications on experimental heartbeat interval datasets (i.e., healthy subjects undergoing postural changes and patients with severe cardiac heart failure) are reported. © 2017, Springer International Publishing AG.}, doi = {10.1007/978-3-319-58709-7_8} }  @comment{{jabref-meta: databaseType:bibtex;}}  @inproceedings{barbieri2013increased, title = {Increased instability of heartbeat dynamics in Parkinson's disease}, author = {Barbieri, Riccardo and Citi, Luca and Valenza, Gaetano and Guerrisi, Maria and Orsolini, Stefano and Tessa, Carlo and Diciotti, Stefano and Toschi, Nicola}, booktitle = {Proceedings of Computing in Cardiology}, year = {2013}, address = {Valencia}, month = sep, pages = {89--92}, owner = {lciti}, timestamp = {2015.01.22} }  @inproceedings{Barbieri2014EntropyParkinson, title = {Lower instantaneous entropy of heartbeat dynamics characterizes cognitive impairment in Parkinson's disease}, author = {Barbieri, R. and Valenza, G. and Citi, L. and Guerrisi, M. and Orsolini, S. and Tessa, C. and Diciotti, S. and Toschi, N.}, booktitle = {Proceedings of Computing in Cardiology}, year = {2014}, pages = {81--84}, abstract = {It has been estimated that the incidence of cognitive deficits in Parkinson's disease (PD), ranging from Mild Cognitive Impairment (MCI) to frank dementia, is six-fold compared to that in the general population. Also, PD involves postganglionic sympathetic failure and, in 25% of patients, autonomic failure. PD patients commonly present a range of ANS-dysfunction related symptoms. Since cognitive impairment has been previously linked with cardiovascular dysautonomia in PD, in this paper we investigate whether a link exists between autonomic complexity and MCI in PD. To this end, we employ our recently developed instantaneous measures of complexity, which have been explicitly designed for stochastic time series with binary events that occur in continuous time: the inhomogeneous point-process approximate and sample entropy (ipApEn and ipSampEn, respectively). Experimental results obtained by comparing 8 cognitively preserved (PD-NC) to 8 PD-MCI subjects during resting state demonstrate that grand average values of ipSampEn are able to differentiate the two groups. This suggests that a significant loss of time-varying cardiovascular complexity is associated with MCI in PD. Importantly, no other heart rate variability (HRV) measures differed significantly between groups, possibly pointing toward subtle autonomic changes (not detectable through conventional HRV analysis) which accompany the initial stage of cognitive impairment in PD.}, owner = {lciti}, timestamp = {2016.01.06} }  @inproceedings{Carpaneto2011ActivitiesPNSNeuralInterf, title = {Activities on {PNS} Neural Interfaces for the Control of Hand Prostheses}, author = {Carpaneto, Jacopo and Cutrone, Annarita and Bossi, Silvia and Sergi, Pier Nicola and Citi, Luca and Rigosa, Jacopo and Rossini, Paolo Maria and Micera, Silvestro}, booktitle = {Proceedings of the 33rd {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2011}, address = {Boston}, month = sep, abstract = {The development of interfaces linking the human nervous system with artificial devices is an important area of research. Several groups are working on the development of devices able to restore sensory-motor function in subjects affected by neurological disorders, injuries or amputations. Neural electrodes implanted in peripheral nervous system, and in particular intrafascicular electrodes, seem to be a promising approach for the control of hand prosthesis thanks to the possibility to selectively access motor and sensory fibers for decoding motor commands and delivering sensory feedback. In this paper, activities on the use of PNS interfaces for the control of hand prosthesis are presented. In particular, the design and feasibility study of a self-opening neural interface is presented together with the decoding of ENG signals in one amputee to control a dexterous hand prosthesis.}, check = {2011.09.07}, doi = {10.1109/IEMBS.2011.6091148}, owner = {lciti}, timestamp = {2011.09.07} }  @inproceedings{Chen2011InstantAssessAutonomicCardiovControlAnesthesia, title = {Instantaneous Assessment of Autonomic Cardiovascular Control During General Anesthesia}, author = {Chen, Zhe and Citi, Luca and Purdon, Patrick L and Brown, Emery N and Barbieri, Riccardo}, booktitle = {Proceedings of the 33rd {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2011}, address = {Boston}, month = sep, abstract = {We present a comprehensive probabilistic point process framework to estimate and monitor the instantaneous heartbeat dynamics as related to specific cardiovascular control mechanisms and hemodynamics. Assessment of the model's statistics is established through the Wiener-Volterra theory and a multivariate autoregressive (AR) structure. A variety of instantaneous cardiovascular metrics, such as heart rate (HR), heart rate variability (HRV), respiratory sinus arrhythmia (RSA), and baroreceptor-cardiac reflex (BRS), can be rigorously derived within a parametric framework and instantaneously updated with an adaptive algorithm. Instantaneous metrics of nonlinearity, such as the bispectrum of heartbeat intervals, can also be derived. We have applied the proposed point process framework to experimental recordings from healthy subjects in order to monitor cardiovascular regulation under propofol anesthesia. Results reveal interesting dynamic trends across different pharmacological interventions, confirming the ability of the algorithm to track important changes in cardiorespiratory elicited interactions, and pointing at our mathematical approach as a promising monitoring tool for an accurate, noninvasive assessment of general anesthesia.}, check = {2011.09.07}, doi = {10.1109/IEMBS.2011.6092083}, owner = {lciti}, timestamp = {2011.09.07} }  @inproceedings{Cinel2004PossSourPercErrorP300, title = {Possible sources of perceptual errors in {P300}-based speller paradigm}, author = {Caterina Cinel and Riccardo Poli and Luca Citi}, booktitle = {Proceedings of the 2nd International {BCI} Workshop and Training Course}, year = {2004}, address = {Graz}, month = sep, pages = {39--40}, abstract = {Some perceptual phenomena can interfere with character identification in Farwell and Donchin's P300-based speller paradigm: attentional blink, repetition blindness and other effects caused by attentional limits. In the paper we discuss these and provide empirical evidence for one class of perceptual errors.}, check = {2010.10.27}, owner = {lciti}, timestamp = {2010.10.27}, url = {http://users.neurostat.mit.edu/lciti/publications_files/Cinel2004PossibleSurcesPerceptErrorsP300.pdf} }  @inproceedings{cinel2013exploration, title = {An exploration of the effects of audio-visual entrainment on Parkinson's disease tremor}, author = {Cinel, C and Poli, R and Citi, L and Roberson, D}, booktitle = {Proceedings of the 6th {IEEE/EMBS} International Conference on Neural Engineering, {NER}}, year = {2013}, organization = {IEEE}, pages = {1562--1565}, doi = {10.1109/NER.2013.6696245}, owner = {lciti}, timestamp = {2015.01.22} }  @inproceedings{Citi2015ElNetMKLMM, title = {Elastic-net constrained multiple kernel learning using a majorization-minimization approach}, author = {Luca Citi}, booktitle = {Proceedings of the 7th Computer Science and Electronic Engineering Conference (CEEC)}, year = {2015}, pages = {29--34}, publisher = {Institute of Electrical and Electronics Engineers ({IEEE})}, abstract = {This papers introduces an algorithm for the solution of multiple kernel learning (MKL) problems with elastic-net constraints on the kernel weights. While efficient algorithms exist for MKL problems with L1- and Lp-norm (p > 1) constraints, a similar algorithm was lacking in the case of MKL under elastic-net constraints. For example, algorithms based on the cutting plane method require large and/or commercial libraries. The algorithm presented here can solve elastic-net constrained MKL problems very efficiently with simple code that does not rely on external libraries (except a conventional SVM solver). Based on majorization-minimization (MM), at each step it optimizes the kernel weights by minimizing a carefully designed surrogate function, called a majorizer, which can be solved in closed form. This improved efficiency and applicability facilitates the inclusion of elastic-net constrained MKL in existing open-source machine learning libraries.}, doi = {10.1109/CEEC.2015.7332695}, owner = {lciti}, timestamp = {2016.01.06} }  @inproceedings{Citi2012PredictingMortality, title = {{P}hysio{N}et 2012 Challenge: Predicting Mortality of {ICU} Patients using a Cascaded {SVM-GLM} Paradigm}, author = {Citi, L. and Barbieri, R.}, booktitle = {Proceedings of Computing in Cardiology}, year = {2012}, address = {Krakow}, month = sep, abstract = {The focus of the PhysioNet/CinC Challenge 2012 is to develop methods for patient-specific prediction of in-hospital mortality using general descriptors recorded at the time of admission to the ICU and up to 37 time-series measurements collected during the first 48 hours after admission. We developed an algorithm that uses both general descriptors and time-series measurements to predict the in-hospital death (IHD) of ICU patients in Event 1, and to provide a probability estimate of IHD in Event 2. Both aggregated variables and general descriptors were used as features of quadratic Support Vector Machine (SVM) classifiers. Six SVMs were trained using, for each one, all the positive examples plus, in turn, one sixth of the negative examples in the training set. Finally, a Generalized Linear Model with probit link was used to predict the probability of IHD for Event 2 using the raw outputs of the six SVMs as regressors. A positive binary prediction of IHD for Event 1 was made when the probability estimate was higher than an optimized threshold. Official final results of the challenge reported that our entry achieved an Event 2 score of 17.8835, which is the best score out of the total 23 submissions, and Event 1 score of 0.534454 (second best score).}, check = {2012.12.13}, owner = {lciti}, timestamp = {2012.12.13}, url = {http://cinc.mit.edu/archives/2012/pdf/0257.pdf} }  @inproceedings{Citi2011InstantMonitoringSleepFragmentPointProcess, title = {Instantaneous Monitoring of Sleep Fragmentation by Point Process Heart Rate Variability and Respiratory Dynamics}, author = {Citi, Luca and Bianchi, Matt T. and Klerman, Elizabeth B. and Barbieri, Riccardo}, booktitle = {Proceedings of the 33rd {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2011}, address = {Boston}, month = sep, abstract = {We present a novel, automatic point-process approach that is able to provide continuous, instantaneous estimates of heart rate variability (HRV) and respiratory sinus arrhythmia (RSA) in long duration data recordings such as those during an entire night of sleep. We analyze subjects with and without sleep apnea who underwent diagnostic polysomnography. The proposed algorithm is able to quantify multi-scale high time resolution autonomic signatures of sleep fragmentation, such as arousals and stage transitions, throughout an entire night. Results demonstrate the ability of our methods to track fast dynamic transitions from sleep to wake and between REM sleep and other sleep stages, providing resolution details not available in sleep scoring summaries. An automatic threshold-based procedure is further able to detect brief arousals, with the instantaneous indices characterizing specific arousal dynamic signatures.}, check = {2011.09.07}, doi = {10.1109/IEMBS.2011.6091906}, owner = {lciti}, timestamp = {2011.09.07} }  @inproceedings{Citi2011PointProcessHeartBeatDetectionCorrection, title = {A Point Process Local Likelihood Algorithm for Robust and Automated Heart Beat Detection and Correction}, author = {Citi, Luca and Brown, Emery N. and Barbieri, Riccardo}, booktitle = {Proceedings of Computing in Cardiology}, year = {2011}, address = {Hangzhou}, month = sep, abstract = {Robust and automated classification and correction of ECG-derived heart beats are a necessary prerequisite for an accurate real-time estimation of measures of heart rate variability and cardiovascular control. In particular, the low quality of the signal, as well as the presence of recurring arrhythmic events, may significantly affect estimation accuracy. We here present a novel point process based method for a real time R-R interval error detection and correction. Results of detection analysis over data from the benchmark MIT-BIH arrhythmia database demonstrate that the proposed algorithm achieves 99.97\% accuracy (98.23\% sensitivity, 99.98\% specificity and 95.69\% positive predictive value), outperforming state-of-the-art algorithms. Further results on simulated data demonstrate the efficacy of the detection and correction method.}, check = {2011.09.07}, owner = {lciti}, timestamp = {2011.09.07} }  @inproceedings{Citi2006CharactTFLIFENeurRespContrCybernHand, title = {Characterization of {tfLIFE} Neural Response for the Control of a Cybernetic Hand}, author = {Luca Citi and Jacopo Carpaneto and Ken Yoshida and Klaus-Peter Hoffmann and Klaus-Peter Koch and Paolo Dario and Silvestro Micera}, booktitle = {Proceedings of the 1st {IEEE}/{RAS-EMBS} International Conference on Biomedical Robotics and Biomechatronics, {B}io{R}ob}, year = {2006}, address = {Pisa}, month = feb, pages = {477 -482}, abstract = {The development of interfaces that link the human nervous system with robotic devices or man-made devices has been a main area of research for several groups in the world. These groups focus on the restoration of motor and sensory function to those with degenerative diseases, injury or in amputees. A key component is these systems is a fast, intuitive, bidirectional interface between the biological and mechatronic systems that allows the robotic limb to be controlled as if it were a natural part of the body. Current hand prostheses use electromyographic (EMG) signals, but are limited to a small number of channels and to sensing volition. To achieve sensory feedback and a higher number of control channels, a neuroprosthetic interface are required. In the present study, thin-film longitudinal intra-fascicular electrodes (tfLIFE) were implanted in the sciatic nerve of the rabbit. Various sensory stimuli were applied to the hind limb of the rabbit and the elicited signals were recorded using the tfLIFEs. These signals were processed to determine whether the different modes of information could be decoded. Signals were Kalman filtered, wavelet denoised, and spike sorted. The classes of spikes found were then used to infer the stimulus applied to the rabbit. Although the signals acquired from a single tLIFE gave poor stimulus recognition, the combination of the signals from multiple sites led to better results. The spike sorting algorithm is also helped by the use of temporal correlation between the channels. A direct outcome of the results is the possibility of increasing the number of channels of control possible with a prosthetic limb}, check = {2010.10.27}, doi = {10.1109/BIOROB.2006.1639134}, keywords = {EMG;Kalman filter;cybernetic hand;electromyographic signal;hand prostheses;human nervous system;hybrid bionic system;motor function;neural response;neuroprosthetic interface;prosthetic limb;robotic device;sciatic nerve;sensory function;sensory stimuli;spike sorting algorithm;temporal correlation;thin-film longitudinal intra-fascicular electrode;wavelet denoising;biocybernetics;biomedical electrodes;electromyography;medical robotics;neurophysiology;prosthetics;}, owner = {lciti}, timestamp = {2006.06.16} }  @inproceedings{Citi2011PointProcessAnalysisMuscleSpindles, title = {Point-Process Analysis of Neural Spiking Activity of Muscle Spindles Recorded from Thin-Film Longitudinal Intrafascicular Electrodes}, author = {Citi, Luca and Djilas, Milan and Azevedo-Coste, Christine and Yoshida, Ken and Brown, Emery N and Barbieri, Riccardo}, booktitle = {Proceedings of the 33rd {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2011}, address = {Boston}, month = sep, pages = {2311--2314}, abstract = {Recordings from thin-film Longitudinal Intra-Fascicular Electrodes (tfLIFE) together with a wavelet-based denoising and a correlation-based spike sorting algorithm, give access to firing patterns of muscle spindle afferents. In this study we use a point process probability structure to assess mechanical stimulus-response characteristics of muscle spindle spike trains. We assume that the stimulus intensity is primarily a linear combination of the spontaneous firing rate, the muscle extension, and the stretch velocity. By using the ability of the point process framework to provide an objective goodness of fit analysis, we were able to distinguish two classes of spike clusters with different statistical structure. We found that spike clusters with higher SNR have a temporal structure that can be fitted by an inverse Gaussian distribution while lower SNR clusters follow a Poisson-like distribution. The point process algorithm is further able to provide the instantaneous intensity function associated with the stimulus-response model with the best goodness of fit. This important result is a first step towards a point process decoding algorithm to estimate the muscle length and possibly provide closed loop Functional Electrical Stimulation (FES) systems with natural sensory feedback information.}, check = {2011.09.07}, doi = {10.1109/IEMBS.2011.6090581}, owner = {lciti}, timestamp = {2011.09.07}, url = {http://users.neurostat.mit.edu/lciti/publications_files/Citi2011PointProcessAnalysisMuscleSpindles.pdf} }  @inproceedings{Citi2014RankMSE, title = {Rank-based Multi-Scale Entropy Analysis of Heart Rate Variability}, author = {Citi, Luca and Guffanti, Giulia and Mainardi, Luca}, booktitle = {Proceedings of Computing in Cardiology}, year = {2014}, address = {Boston}, month = sep, owner = {lciti}, timestamp = {2015.01.23}, url = {http://cinc.org/archives/2014/pdf/0597.pdf} }  @inproceedings{Citi2010PointProcessHRVSleepDeprivation, title = {Point process heart rate variability assessment during sleep deprivation}, author = {Citi, Luca and Klerman, Elizabeth B. and Brown, Emery N. and Barbieri, Riccardo}, booktitle = {Proceedings of Computing in Cardiology}, year = {2010}, address = {Belfast}, month = sep, abstract = {To investigate the potential relationships between Heart rate variability (HRV) and objective performance-subjective alertness measures during sleep deprivation, a novel point process algorithm was applied to ECG data from healthy young subjects in a 52-hour Constant Routine protocol, which includes sleep deprivation. Our algorithm is able to estimate the time-varying behavior of the HRV spectral indexes in an on-line instantaneous fashion. Results demonstrate the ability of our framework to provide high time-resolution sympatho-vagal dynamics as measured by spectral low frequency (LF) and high frequency (HF) power. Correlation analysis on individual subjects reveals a relevant correspondence between LF/HF and subjective alertness during the initial hours of sleep deprivation. At longer times awake, high correlation levels between LF/HF and objective performance indicate an increasing sympathetic drive as performance measures worsen. These results suggest that our point-process based HRV assessment could aid in real-time prediction of performance-alertness.}, check = {TODO}, owner = {lciti}, timestamp = {2010.10.27}, url = {http://web.cinc.org/2010/preprints/315.pdf} }  @inproceedings{Citi2015LightWAVE_Client, author = {L. Citi and C. Olariu and R. Barbieri}, title = {A LightWAVE client for semi-automated annotation of Heart Beats from ECG Time Series}, booktitle = {Proceedings of Computing in Cardiology}, year = {2015}, pages = {605-608}, month = sep, abstract = {LightWAVE is an open-source web-based software for viewing ECGs and other physiologic waveforms and associated annotations (such as heart-beat markers). At present, most users run the raw ECG through an automated QRS detector and later use LightWAVE to review and correct the detected heart beats. Although this 2-stage procedure may work well with clean signals, it is inefficient and time consuming when the recordings are contaminated by noise, artefacts or recurring ectopic events. To overcome this limitation, we customized the LightWAVE client to allow automated and semi-automated annotation of heart beats from ECG time series. In semi-automatic mode, the algorithm automatically identifies most QRS complexes and stops - asking for manual intervention - whenever the confidence of a detection falls below a given threshold. Additionally, the software now shows the series of inter-beat intervals, which is an invaluable tool to easily spot R-wave misdetections and genuine arrhythmias. The new client introduces further additional features compared to the standard version, for example the possibility of importing raw signals from local CSV files and of exporting the current plot in SVG format. Overall, our customized client extends the functionality of LightWAVE and brings it closer to one of its design goals, i.e. to provide a comfortable and efficient method of annotating physiologic data.}, doi = {10.1109/CIC.2015.7410983}, issn = {2325-8861}, keywords = {electrocardiography;medical signal detection;medical signal processing;time series;ECG time series;LightWAVE client;QRS complexes;R-wave misdetections;arrhythmias;artefacts;automated QRS detector;ectopic events;electrocardiography;heart beat detection;interbeat intervals;noise;open-source Web-based software;semiautomated annotation;Detection algorithms;Electrocardiography;Heart beat;Physiology;Servers;Software;Software algorithms} }  @inproceedings{Citi2009ExploitingP300AmplitudeVariations, title = {Exploiting {P300} Amplitude Variations Can Improve Classification Accuracy in {Donchin's} {BCI} Speller}, author = {Luca Citi and Riccardo Poli and Caterina Cinel}, booktitle = {Proceedings of the 3rd {IEEE/EMBS} International Conference on Neural Engineering, {NER}}, year = {2009}, address = {Antalya}, month = apr, abstract = {The P300 is an endogenous component of EEG event related potentials which is elicited by rare and significant stimuli. P300s are used increasingly frequently in Brain Computer Interfaces (BCI) because, being naturally elicited in response to external stimuli, users do not need special training. However, P300 waves are hard to detect and, therefore, multiple stimulus presentations are needed before an interface can make a reliable decision. While significant improvements have been made in the detection of P300s, no particular attention has been paid to the variability in shape and timing of P300 waves and its exploitation in BCI. In this paper we start filling this gap, by first documenting and then exploiting a modulation in amplitude of P300 caused by target-to-target interval (TTI) differences. We demonstrate this within the context of the Donchin's speller, which is perhaps the best known example of a BCI system relying on the detection P300 waves, where target-to-target interval variations are induced by stimuli randomisation. In particular we show that by specialising detectors to work with P300s elicited with each TTI, we can further improve the performance of the best known Donchin's speller with minimal changes.}, check = {2010.10.27}, doi = {10.1109/NER.2009.5109337}, owner = {lciti}, timestamp = {2009.05.13} }  @inproceedings{CitiPoliSepulCinel2006AnalogueP300_BasedBCI, title = {Analogue {P300-based} {BCI} pointing device}, author = {Luca Citi and Riccardo Poli and Caterina Cinel}, booktitle = {Proceedings of the 3rd International {BCI} Workshop and Training Course}, year = {2006}, address = {Graz}, month = sep, pages = {92--93}, abstract = {We propose a P300-based BCI mouse. The system is analogue: the pointer is controlled by directly combining the amplitudes of the outputs produced by a filter in the presence of different stimuli. The system is optimised by a genetic algorithm.}, check = {2010.10.27}, issue = {1}, owner = {lciti}, timestamp = {2010.10.27}, url = {http://users.neurostat.mit.edu/lciti/publications_files/Citi2006AnalogueP300basedBCI.pdf} }  @inproceedings{CitiPoliSepul2004EvolApprFeatSelectAndClassP300BCI, title = {An evolutionary approach to feature selection and classification in {P300}-based {BCI}}, author = {Luca Citi and Riccardo Poli and Francisco Sepulveda}, booktitle = {Proceedings of the 2nd International {BCI} workshop and Training Course}, year = {2004}, address = {Graz}, month = sep, pages = {41--42}, abstract = {We explore the use of evolutionary algorithms in the selection of features and the classification of P300 signals in BCI. As a result we have found new ways to process and combine EEG signals to improve detection.}, aka = {CitiPoliSepul_2004_EvolApprFeatSelectAndClassP300BCI}, check = {2010.10.27}, owner = {lciti}, timestamp = {2010.10.27}, url = {http://users.neurostat.mit.edu/lciti/publications_files/Citi2004EvolApprFeatSelectAndClassP300BCI.pdf} }  @inproceedings{Citi2012InstantaneousLyapunov, title = {Instantaneous estimation of high-order nonlinear heartbeat dynamics by {L}yapunov exponents}, author = {Citi, L. and Valenza, G. and Barbieri, R.}, booktitle = {Proceedings of the 34th {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2012}, address = {San Diego}, pages = {13--16}, abstract = {This paper introduces a novel methodology able to provide time varying estimates of the Lyapunov Spectrum within a point process framework. The algorithm is applied to ECG-derived data to characterize heartbeat nonlinear dynamics by using a cubic autoregressive point process model. Estimation of the model parameters is ensured by the Laguerre expansion of the Wiener-Volterra kernels along with a maximum local log-likelihood procedure. In addition to the instantaneous Lyapunov exponents, as well as indices related to higher order dynamic polyspectra, our method is also able to provide all the instantaneous time domain and frequency domain measures of instantaneous heart rate (HR) and heart rate variability (HRV) previously considered. Experimental results show that our method is able to track complex cardiovascular control dynamics during fast transitional gravitational changes.}, check = {2012.12.13}, doi = {10.1109/EMBC.2012.6345859}, owner = {lciti}, timestamp = {2012.12.13} }  @inproceedings{Citi2012MonitoringAnesthesiaLyapunov, title = {Monitoring heartbeat nonlinear dynamics during general anesthesia by using the instantaneous dominant {L}yapunov exponent}, author = {Citi, L. and Valenza, G. and Purdon, P.L. and Brown, E.N. and Barbieri, R.}, booktitle = {Proceedings of the 34th {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2012}, address = {San Diego}, pages = {3124--3127}, abstract = {We present a novel methodology for instantaneous estimation of quantitative correlates of depth of Anesthesia from noninvasive electrocardiographic recordings. The analysis is based on a point process model of heartbeat dynamics that allows for continuous tracking of linear and nonlinear HRV indices, including a novel instantaneous assessment of the Lyapunov Spectrum by using a cubic autoregressive formulation. The effective estimation of the model parameters is ensured by the Laguerre expansion of the Wiener-Volterra kernels along with the maximum local log-likelihood procedure. We apply the proposed assessment to experimental recordings from healthy subjects during propofol anesthesia. The new assessment reveals novel time-varying complex heartbeat dynamics that underlie the quasi-periodic heartbeat fluctuations elicited by the sympatho-vagal balance. Results suggest that such quantification provides important information which is independent from the standard autonomic assessment and significantly correlated with loss of consciousness. Further investigation will focus on evolving our mathematical approach towards a promising monitoring tool for an accurate, noninvasive assessment of general anesthesia.}, check = {2012.12.13}, doi = {10.1109/EMBC.2012.6346626}, owner = {lciti}, timestamp = {2012.12.13} }  @inproceedings{DiGiovanna2008InferringStabilityLIFE, title = {Inferring the stability of LIFE through Brain Machine Interfaces.}, author = {Jack DiGiovanna and Luca Citi and Ken Yoshida and Jacopo Carpaneto and Jose C Principe and Justin C Sanchez and Silvestro Micera}, booktitle = {Proceedings of the 30th {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2008}, address = {Vancouver}, month = aug, pages = {2008--2011}, volume = {2008}, abstract = {We examine neural signals from Longitudinally implanted Intra-Fascicular Electrodes (LIFE) in a chronic, rabbit model. Translation-invariant wavelet de-noising methods are used to improve S\%R. Then traditional template-based spike sorting is applied to discriminate single units. We investigate the effect of discriminating between identified units on Brain Machine Interface (BMI) decoding performance. We infer the stability of LIFE based on decoding performance with and without current BMI methods to counter-act electrode neural signal degradation.}, check = {2010.10.27}, doi = {10.1109/IEMBS.2008.4649584}, institution = {Dept. of Biomedical Engineering, University of Florida, Gainesville, FL 32611, USA. jfd134@ufl.edu}, keywords = {Action Potentials; Algorithms; Animals; Electrodes, Implanted; Electrophysiology; Female; Models, Neurological; Muscle, Skeletal; Rabbits; Signal Processing, Computer-Assisted; User-Computer Interface}, owner = {lciti}, pmid = {19163087}, timestamp = {2009.05.13} }  @inproceedings{Ellis2011PointProcessGaitVariability, title = {A point process approach for analyzing gait variability dynamics}, author = {Ellis, Robert J and Citi, Luca and Barbieri, Riccardo}, booktitle = {Proceedings of the 33rd {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2011}, address = {Boston}, month = sep, abstract = {We present a novel statistical paradigm for modeling and analysis of gait variability which captures the natural point process structure of gait intervals and allows for definition of new measures instantaneous mean and standard deviation. We validate our model using two existing data sets from physionet.org. Results show an excellent model fit and yield insights into the underlying statistical structure behind human gait. Statistical analyses further corroborate previous findings of increased variability in gait at different speeds, both self-paced and metronome-paced, and reveal a significant increase in gait variability in Parkinson's subjects, as compared to young and elderly healthy subjects. These results indicate the validity of a point process approach to the analysis of gait, and the potential utility of incorporating instantaneous measures of gait into diagnostic or patient monitoring applications.}, check = {2011.09.07}, doi = {10.1109/IEMBS.2011.6090475}, owner = {lciti}, timestamp = {2011.09.07} }  @inproceedings{greco2014electrodermal, title = {Electrodermal activity processing: A convex optimization approach}, author = {Greco, Alberto and Lanata, Antonio and Valenza, Gaetano and Scilingo, Enzo Pasquale and Citi, Luca}, booktitle = {Proceedings of the 36th {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2014}, month = aug, organization = {IEEE}, pages = {2290--2293}, doi = {10.1109/EMBC.2014.6944077}, owner = {lciti}, timestamp = {2015.01.22} }  @inproceedings{Menon2006ProspectsOfBCIForSpace, title = {Prospects of {B}rain-{M}achine {I}nterfaces for space system control}, author = {Carlo Menon and de Negueruela, Cristina and del R. Mill\'an, Jos\'e and Oliver Tonet and Federico Carpi and Michael Broschart and Pierre Ferrez and Anna Buttfield and Paolo Dario and Luca Citi and Cecilia Laschi and Mario Tombini and Francisco Sepulveda and Riccardo Poli and Ramaswamy Palaniappan and Franca Tecchio and Rossini, Paolo Maria and De Rossi, Danilo}, booktitle = {Proceedings of the 57th International Astronautical Congress}, year = {2006}, address = {Valencia}, month = oct, abstract = {The dream of controlling and guiding computer-based systems using human brain signals has slowly but steadily become a reality. The available technology allows real-time implementation of systems that measure neuronal activity, convert their signals, and translate their output for the purpose of controlling mechanical and electronic systems. This paper describes the state of the art of non-invasive brain-machine interfaces (BMIs) and critically investigates both the current technological limits and the future potential that BMIs have for space applications. We present an assessment of the advantages that BMIs can provide and justify the preferred candidate concepts for space applications together with a vision of future directions for their implementation.}, check = {2011.08.17}, owner = {lciti}, timestamp = {2011.08.17} }  @inproceedings{Micera2009ControlRobotHandByNeuralSignalsPNS, title = {On the control of a robot hand by extracting neural signals from the {PNS}: preliminary results from a human implantation.}, author = {S. Micera and J. Rigosa and J. Carpaneto and L. Citi and S. Raspopovic and E. Guglielmelli and A. Benvenuto and L. Rossini and G. Di Pino and G. Cavallo and M. C. Carrozza and C. Cipriani and K. P. Hoffmann and P. Dario and P. M. Rossini}, booktitle = {Proceedings of the 31st {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2009}, address = {Minneapolis}, month = sep, pages = {4586--4589}, volume = {2009}, abstract = {The development of hybrid neuroprosthetic systems (HBSs) linking the human nervous system with artificial devices is an important area of research that is currently addressed by several groups to restore sensorimotor function in people affected by different disabilities. It is particularly important to establish a fast, intuitive, bidirectional flow of information between the nervous system of the user and the smart robotic device. Among the possible solutions to achieve this goal, interfaces with the peripheral nervous system and in particular intraneural electrodes can represent an interesting choice. In the present study, thin-film longitudinal intra-fascicular electrodes were implanted in the median and ulnar nerves of an amputee. The possibility of restoring the bidirectional link between the subject and the external world was investigated during a 4 week trial. The result showed that both the extraction of motor information and the restoration of sensory function are possible.}, check = {2011.01.12}, doi = {10.1109/IEMBS.2009.5332764}, institution = {ARTS Lab, Scuola Superiore Sant'Anna, Pisa, Italy. micera@sssup.it}, keywords = {Algorithms; Amputees; Artificial Limbs; Electrodiagnosis, methods; Evoked Potentials, Motor, physiology; Humans; Man-Machine Systems; Median Nerve, physiology; Peripheral Nervous System, physiology; Robotics, methods; Signal Processing, Computer-Assisted; Ulnar Nerve, physiology}, owner = {lciti}, pmid = {19963845}, timestamp = {2010.10.27} }  @inproceedings{Micera2006ExperDevelopNewGenerElectr, title = {Experiments on the development and use of a new generation of intra-neural electrodes to control robotic devices}, author = {Micera, S. and Sergi, P.N. and Carpaneto, J. and Citi, L. and Bossi, S. and Koch, K.-P. and Hoffmann, K.-P. and Menciassi, A. and Yoshida, K. and Dario, P.}, booktitle = {Proceedings of the 28th {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2006}, address = {New York City}, month = sep, pages = {2940 -2943}, abstract = {The development of interfaces linking the human nervous system with artificial devices is an important area of research and several groups are now addressing it. Interfaces represent the key enabling technology for the development of devices usable for the restoration of motor and sensory function in subjects affected by neurological disorders, injuries or amputations. For example, current hand prostheses use electromyographic (EMG) signals to extract volitional commands but this limits the possibility of controlling several degrees of freedom and of delivering sensory feedback. To achieve these goals, implantable neural interfaces are required. Among the candidate interfaces with the peripheral nervous system intra-neural electrodes seem to be an interesting solution due to their bandwidth and ability to access volition and deliver sensory feedback. However, several drawbacks have to be addressed in order to increase their usability. In this paper, experiments to address many of these issues are presented as part of the development of a new generation of intra-neural electrodes. The results showed seem to confirm that these new interfaces seem to have interesting properties and that they can represent a significant improvement of the state of the art. Extensive experiments will be carried out in the future to validate these results}, check = {2010.10.27}, doi = {10.1109/IEMBS.2006.260346}, issn = {1557-170X}, keywords = {PNS;artificial device;current hand prostheses;electromyographic signal;human nervous system;implantable neural interface;intraneural electrodes;neuro-robotics;neurological disorder;peripheral nervous system;robotic device control;sensory feedback;biomedical electrodes;medical robotics;neurophysiology;prosthetics;}, owner = {lciti}, pmid = {17945747}, timestamp = {2010.10.27} }  @inproceedings{Orini2012BivariatePointProcessPTT, title = {Bivariate point process modeling and joint non-stationary analysis of pulse transit time and heart period}, author = {Orini, M. and Citi, L. and Barbieri, R.}, booktitle = {Proceedings of the 34th {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2012}, address = {San Diego}, pages = {2831--2834}, abstract = {Pulse transit time (PTT) is strictly related to pulse wave velocity and may be used for non-invasive monitoring of arterial stiffness and pressure, whose assessment is fundamental to detect cardiovascular dysfunctions. We propose a new model to characterize instantaneous PTT dynamics, and the interactions between PTT and R-R interval (RRI). In this model, PTT is described as a point process whose probability function depends on previous PTT and RRI values. From the model coefficients, instantaneous powers, coherence and directed coherence of each spectral component are estimated. We used this framework to study the changes that tilt table test provoked in PTT and RRI dynamics in 17 healthy subjects. Time-varying spectral and coherence analysis revealed that, although PTT and RRI were locally correlated, direct contribution of RRI on PTT was low during the entire test in high frequency band, and just after postural changes in low frequency band. We conclude that PTT may add valuable information for a more accurate characterization of cardiovascular regulation.}, check = {2012.12.13}, doi = {10.1109/EMBC.2012.6346553}, owner = {lciti}, timestamp = {2012.12.13} }  @inproceedings{orini2013characterization, title = {Characterization of the causal interactions between depolarization and repolarization temporal changes in unipolar electrograms}, author = {Orini, Michele and Citi, Luca and Hanson, Ben M and Taggart, Peter and Lambiase, Pier D}, booktitle = {Proceedings of Computing in Cardiology}, year = {2013}, address = {Valencia}, month = sep, pages = {719--722}, owner = {lciti}, timestamp = {2015.01.22} }  @inproceedings{Orini2012TetravariatePointProcess, title = {Tetravariate Point-Process Model for the Continuous Characterization of Cardiovascular-Respiratory Dynamics during Passive Postural Changes}, author = {Orini, M. and Valenza, G. and Citi, L. and Barbieri, R.}, booktitle = {Proceedings of Computing in Cardiology}, year = {2012}, address = {Krakow}, month = sep, abstract = {In this study, we present a new methodology for time-varying characterization of cardiovascular (CV) control, which includes RR interval (RRI), systolic arterial pressure (SAP), respiration (RSP) and pulse transit time (PTT). Within a multivariate model, CV dynamics are represented as stochastic point processes whose means has a tetravariate autoregressive structure. Such framework provides the simultaneous time-frequency assessment of: (i) both arms of the SAP-RRI loop, along baroreflex and mechanical feedforward pathways; (ii) Respiratory sinus arrhythmia (RSA), through the direct evaluation of the interactions between RSP and the RRI; (iii) the coupling between cardiorespiratory activity and vascular tone through quantification of the interactions between PTT and the other CV variables. We validated the model by characterizing CV control in 16 healthy subjects during a tilt table test, and we were able to confirm a satisfactory model's goodness-of-fit. We further estimated transfer function gains, instantaneous powers and directed coherences, and observed that RSP strongly drove respiratory-related oscillations in all the other CV variables, and that PTT depended on RRI dynamics rather than blood pressure variations. During head-up tilt, baroreflex sensitivity and RSA decreased, while the gain from RRI to SAP increased, thus confirming previous physiological characterizations.}, check = {2012.12.13}, owner = {lciti}, timestamp = {2012.12.13}, url = {http://cinc.mit.edu/archives/2012/pdf/0273.pdf} }  @inproceedings{Pani2011RealTimeProcessingTfLIFE, title = {Real-time processing of {tfLIFE} neural signals on embedded {DSP} platforms: A case study}, author = {Pani, Danilo and Usai, Francesco and Citi, Luca and Raffo, Luigi}, booktitle = {Proceedings of the 5th {IEEE/EMBS} International Conference on Neural Engineering, {NER}}, year = {2011}, address = {Cancun}, month = apr, pages = {44--47}, abstract = {Spike sorting is a typical neural processing technique aimed at identifying the firing activity of individual neurons. It plays a different role in the processing of the signals coming either from a single electrode or an electrode array. In presence of highly noisy recordings, a preliminary denoising stage is required in order to improve the SNR. Despite the significant number of studies in the field, only a few of them deal with peripheral nervous system (PNS) recordings and often the possibility of a real-time implementation is only hinted without any real implementation study. In this paper, a real-time PNS signal processing and classification technique is presented end evaluated on real elec-troneurographic signals taken from the sciatic nerve of rats. A state-of-the-art algorithm, composed of a wavelet denoising preprocessing stage followed by a correlation-based spike sorting and a support vector machine, has been adapted to work on-line in order to improve the processing efficiency while preserving at the most its effectiveness. The algorithm provides some level of adaptiveness with respect to an off-line implementation. On average, the correct classification reach 92.24% with isolated errors that can be easily filtered out. Cycle-accurate profiling results on an off-the-shelf Digital Signal Processor demonstrate the real-time performance.}, check = {2011.09.07}, doi = {10.1109/NER.2011.5910485}, owner = {lciti}, timestamp = {2011.09.07} }  @inproceedings{Poli2011GPApproachDetectArtifact, title = {A genetic programming approach to detecting artifact-generating eye movements from EEG in the absence of electro-oculogram}, author = {Poli, Riccardo and Cinel, Caterina and Citi, Luca and Salvaris, Mathew}, booktitle = {Proceedings of the 5th {IEEE/EMBS} International Conference on Neural Engineering, {NER}}, year = {2011}, address = {Cancun}, month = apr, pages = {416--421}, abstract = {In this paper we use genetic programming an evolutionary program-induction technology to evolve algorithms that accurately approximate the behaviour of two standard detectors of ocular movement based on Electro-oculogram ({EOG}). The prediction is based entirely on {EEG} signals, i.e., without using {EOG}, making it possible to detect eye movements even in data recorded without {EOG} or eye tracking. Experimental results with this approach are very encouraging.}, check = {2011.09.07}, doi = {10.1109/NER.2011.5910575}, owner = {lciti}, timestamp = {2011.09.07} }  @inproceedings{PoliCinelCitiSepulv2007EvolutionaryBCI, title = {Evolutionary Brain Computer Interfaces.}, author = {Riccardo Poli and Caterina Cinel and Luca Citi and Francisco Sepulveda}, booktitle = {Proceedings of the EvoWorkshops}, year = {2007}, address = {Valencia}, month = apr, pages = {301--310}, abstract = {We propose a BCI mouse and speller based on the manipulation of P300 waves in EEG signals. The 2---D motion of the pointer on the screen is controlled by directly combining the amplitudes of the output produced by a filter in the presence of different stimuli. This filter and the features to be combined within it are optimised by a GA.}, check = {2010.10.27}, owner = {lciti}, timestamp = {2010.10.27} }  @inproceedings{Poli2010EigenbrainsFreeVibrationalModes, title = {Eigenbrains: the Free Vibrational Modes of the Brain as a New Representation for {EEG}}, author = {Poli, Riccardo and Citi, Luca and Salvaris, Mathew and Cinel, Caterina and Sepulveda, Francisco}, booktitle = {Proceedings of the 32nd {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2010}, address = {Buenos Aires}, month = sep, pages = {6011--6014}, volume = {2010}, abstract = {We present a new transform for EEG signals whose basis functions are well suited to represent the large-scale dynamics associated with event related potentials. The method involves instantiating an approximate model of the electrical properties of the brain as a conductor medium and then studying the free vibrational modes of the model. These form a set of basis functions, which we call eigenbrains, that can be used to meaningfully re-represent the brain's electrical activity. Eigenbrains are compared to principal component analysis and independent component analysis to highlight differences and similarities.}, check = {2011.09.07}, doi = {10.1109/IEMBS.2010.5627593}, owner = {lciti}, pmid = {21097112}, timestamp = {2011.09.07} }  @inproceedings{Poli2009MemoryWithMemoryTreeBasedGP, title = {Memory with Memory in Tree-Based Genetic Programming}, author = {Poli, Riccardo and Mcphee, Nicholas F. and Citi, Luca and Crane, Ellery}, booktitle = {Proceedings of the 12th European Conference on Genetic Programming, EuroGP '09}, year = {2009}, address = {T\"{u}bingen}, month = apr, pages = {25--36}, abstract = {In recent work on linear register-based genetic programming (GP) we introduced the notion of Memory-with-Memory (MwM), where the results of operations are stored in registers using a form of soft assignment which blends a result into the current content of a register rather than entirely replace it. The MwM system yielded very promising results on a set of symbolic regression problems. In this paper, we propose a way of introducing MwM style behaviour in tree-based GP systems. The technique requires only very minor modifications to existing code, and, therefore, is easy to apply. Experiments on a variety of synthetic and real-world problems show that MwM is very beneficial in tree-based GP, too.}, check = {2010.10.28}, doi = {10.1007/978-3-642-01181-8_3}, isbn = {978-3-642-01180-1}, owner = {lciti}, timestamp = {2010.10.28} }  @inproceedings{Salvaris2010ExploringMultipleProtocolsBCIMouse, title = {Exploring Multiple Protocols for a Brain-Computer Interface Mouse}, author = {Salvaris, Mathew and Cinel, Caterina and Poli, Riccardo and Citi, Luca and Sepulveda, Francisco}, booktitle = {Proceedings of the 32nd {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2010}, address = {Buenos Aires}, month = sep, pages = {4189--4192}, abstract = {In recent years, various visual protocols have been explored for {P300}-based {BCI}. In stimulus-driven {BCI} paradigms such as {P300} {BCIs} it is vital to optimise the stimulation protocol as much as possible in order to achieve the best performance. Due to the inherent variability between subjects and the complex nature of the brain it is unlikely that an optimal protocol will be identified through a single iteration of random exploration. That is why in this paper we explore 8 different visual protocol configurations based on recent literature, in the hope of identifying key features that can later be used to create further improved protocols. Results indicate that luminosity changes, the standard method of stimulation used in visual {P300} {BCI} protocols, do provide the best performance of the variations presented here.}, check = {2011.09.07}, doi = {{10.1109/IEMBS.2010.5627388}}, owner = {lciti}, pmid = {21096890}, timestamp = {2011.09.07} }  @inproceedings{Sclocco2015CombinSudomotorNerveImpulse_fMRI, title = {Combining sudomotor nerve impulse estimation with fMRI to investigate the central sympathetic response to nausea}, author = {Sclocco, Roberta and Citi, Luca and Garcia, Ronald G. and Cerutti, Sergio and Bianchi, Anna M. and Kuo, Braden and Napadow, Vitaly and Barbieri, Riccardo}, booktitle = {Proceedings of the 37th {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2015}, pages = {4683--4686}, abstract = {The skin conductance (SC) signal is one of the most important non-invasive indirect measures of autonomic outflow. Several mathematical models have been proposed in the literature to characterize specific SC features. In this work, we present a method for the estimation of central control of sudomotor nerve impulse (SMI) function using SC. The method is based on a differential formulation decomposed into two first order differential equations. We validate our estimation framework by applying it on an experimental protocol where eleven motion sickness-prone subjects were exposed to a nauseogenic visual stimulus while SC and fMRI signals were recorded. Our results show an expected significant increase in the mean amplitude of SMI peaks during the highest reported nausea, as well as a decreasing trend during recovery, which was not evident for skin conductance level. Importantly, SMI/fMRI analysis found a negative association between SMI and fMRI signal in orbitofrontal, dorsolateral prefrontal, and posterior insula cortices, consistent with previous studies correlating brain fMRI and microneurographic signals.}, doi = {10.1109/EMBC.2015.7319439}, owner = {lciti}, timestamp = {2016.01.06} }  @inproceedings{valenza2014assessment, title = {Assessment of gait nonlinear dynamics by inhomogeneous point-process models}, author = {Valenza, Gaetano and Citi, Luca and Barbieri, Riccardo}, booktitle = {Proceedings of the 36th {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2014}, month = aug, organization = {IEEE}, pages = {6973--6976}, doi = {10.1109/EMBC.2014.6945232}, owner = {lciti}, timestamp = {2015.01.22} }  @inproceedings{Valenza2013, title = {Instantaneous nonlinear assessment of complex cardiovascular dynamics by laguerre-volterra point process models}, author = {Valenza, Gaetano and Citi, Luca and Barbieri, Riccardo}, booktitle = {Proceedings of the 35th {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2013}, organization = {IEEE}, pages = {6131--6134}, doi = {10.1109/EMBC.2013.6610952}, owner = {lciti}, timestamp = {2015.01.22} }  @inproceedings{valenza2013nonlinear, title = {A nonlinear heartbeat dynamics model approach for personalized emotion recognition}, author = {Valenza, Gaetano and Citi, Luca and Lanata, Antonio and Scilingo, Enzo Pasquale and Barbieri, Riccardo}, booktitle = {Proceedings of the 35th {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2013}, month = aug, organization = {IEEE}, pages = {2579--2582}, doi = {10.1109/EMBC.2013.6610067}, owner = {lciti}, timestamp = {2015.01.22} }  @inproceedings{valenza2013instantaneous, title = {Instantaneous bispectral characterization of the autonomic nervous system through a point-process nonlinear model}, author = {Valenza, G and Citi, L and Scilingo, EP and Barbieri, R}, booktitle = {World Congress on Medical Physics and Biomedical Engineering}, year = {2013}, address = {Beijing, China}, month = may, pages = {530--533}, publisher = {Springer Berlin Heidelberg}, volume = {39}, doi = {10.1007/978-3-642-29305-4_139}, owner = {lciti}, timestamp = {2015.01.22} }  @inproceedings{Valenza2012LaguerrePointProcess, title = {Using {L}aguerre expansion within point-process models of heartbeat dynamics: A comparative study}, author = {Valenza, G. and Citi, L. and Scilingo, E.P. and Barbieri, R.}, booktitle = {Proceedings of the 34th {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2012}, address = {San Diego}, pages = {29--32}, abstract = {Point-process models have been recognized as a distinguished tool for the instantaneous assessment of heartbeat dynamics. Although not thoroughly linked to the physiology, nonlinear models also yield a more accurate quantification of cardiovascular control dynamics. Here, we propose a Laguerre expansion of the linear and nonlinear Wiener-Volterra kernels in order to account for the nonlinear and non-gaussian information contained in the ECG-derived heartbeat series while using a reduced number of parameters. Within an Inverse-Gaussian probability model, up to quadratic nonlinearities were considered to continuously estimate the dynamic spectrum and bispectrum. Results performed on 10 subjects undergoing a stand-up protocol show that this novel methodology improves on the algorithmic performances and, at the same time, more accurately characterizes sympatho-vagal changes to posture.}, check = {2012.12.13}, doi = {10.1109/EMBC.2012.6345863}, owner = {lciti}, timestamp = {2012.12.13} }  @inproceedings{Valenza2014AssessDynAutonChangesPosture, title = {Assessment of dynamic autonomic changes with posture using instantaneous entropy measures}, author = {Valenza, G. and Citi, L. and Scilingo, E. P. and Barbieri, R.}, booktitle = {Proceedings of Computing in Cardiology}, year = {2014}, pages = {489--492}, abstract = {Dynamic analysis provides a powerful methodological framework for characterizing physiological systems. In particular, complex heartbeat dynamics related to autonomic control mechanisms are known to change at each moment in time, and complexity measures have been proven to have prognostic value in both health and disease. Nevertheless, an instantaneous measure of complexity for cardiovascular time series (or any other series of stochastic physiological {\textquotedblleft}events{\textquotedblright}) is still missing. In this study we introduce a mathematical framework serving instantaneous complex estimates of heartbeat dynamics to characterize different activities, tasks, and/or pathological states. In particular we propose new definitions of inhomogeneous point-process approximate and sample entropy where the discrete events are modeled by probability density functions characterizing and predicting the time until the next event occurs as a function of past history. These definitions are built on our previous work employing Laguerre expansions of the Wiener-Volterra autoregressive terms to account for long-term memory. We demonstrate an exemplary study on heartbeat data gathered from healthy subjects undergoing postural changes such as stand-up, slow tilt, and fast tilt. Results show that instantaneous complexity is able to effectively track the complex autonomic changes as they are affected by different postural changes.}, owner = {lciti}, timestamp = {2016.01.06} }  @inproceedings{valenza2014defining, title = {Defining an instantaneous complexity measure for heartbeat dynamics: The inhomogeneous point-process entropy}, author = {Valenza, Gaetano and Citi, Luca and Scilingo, Enzo Pasquale and Barbieri, Riccardo}, booktitle = {Proceedings of the 8th Conference of the European Study Group on Cardiovascular Oscillations, {ESGCO}}, year = {2014}, month = may, pages = {25--26}, doi = {10.1109/ESGCO.2014.6847521}, owner = {lciti}, timestamp = {2015.01.22} }  @inproceedings{valenza2014tracking, title = {Tracking instantaneous entropy in heartbeat dynamics through inhomogeneous point-process nonlinear models}, author = {Valenza, Gaetano and Citi, Luca and Scilingo, Enzo Pasquale and Barbieri, Riccardo}, booktitle = {Proceedings of the 36th {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2014}, month = aug, organization = {IEEE}, pages = {6369--6372}, check = {2015.01.22}, doi = {10.1109/EMBC.2014.6945085}, owner = {lciti}, timestamp = {2015.01.22} }  @inproceedings{Valenza2015InstTransEntropy, title = {Instantaneous transfer entropy for the study of cardio-respiratory dynamics}, author = {Valenza, G. and Faes, L. and Citi, L. and Orini, M. and Barbieri, R.}, booktitle = {Proceedings of the 37th {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2015}, pages = {7885--7888}, abstract = {Measures of transfer entropy have been proposed to quantify the directional coupling and strength between two complex physiological variables. Particular attention has been given to nonlinear interactions within cardiovascular and respiratory dynamics as influenced by the autonomic nervous system. However, standard transfer entropy estimates have shown major limitations in dealing with issues concerning stochastic system modeling, limited observations in time, and the assumption of stationarity of the considered physiological variables. Moreover, standard estimates are unable to track time-varying changes in nonlinear coupling with high resolution in time. Here, we propose a novel definition of transfer entropy linked to inhomogeneous point-process theory. Heartbeat and respiratory dynamics are characterized through discrete time series, and modeled through probability density functions (PDFs) which characterize and predict the time until the occurrence of the next physiological event as a function of the past history. As the derived measures of entropy are instantaneously defined through continuos PDFs, a novel index (the Instantaneous point-process Transfer Entropy, ipT ransfEn) is able to provide instantaneous tracking of the information transfer. The new measure is tested on experimental data gathered from 16 healthy subjects undergoing postural changes, showing fast tracking of the tilting events and low variability during the standing phase.}, doi = {10.1109/EMBC.2015.7320220}, owner = {lciti}, timestamp = {2016.01.06} }  @inproceedings{Valenza2014, title = {Assessing real-time RR-QT frequency-domain measures of coupling and causality through inhomogeneous point-process bivariate models}, author = {Valenza, G and Orini, M and Citi, L and Minchole, A and Pueyo, E and Laguna, P and Barbieri, R}, booktitle = {Proceedings of the 36th {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2014}, month = aug, organization = {IEEE}, pages = {6475--6478}, doi = {10.1109/EMBC.2014.6945111}, owner = {lciti}, timestamp = {2015.01.22} }  @inproceedings{valenza2014assessing, title = {Assessing instantaneous QT variability dynamics within a point-process nonlinear framework}, author = {Valenza, Gaetano and Orini, Michele and Citi, Luca and Minchole, Ana and Pueyo, Ester and Laguna, Pablo and Barbieri, Riccardo}, booktitle = {Proceedings of the 8th Conference of the European Study Group on Cardiovascular Oscillations, {ESGCO}}, year = {2014}, month = may, organization = {IEEE}, pages = {67--68}, doi = {10.1109/ESGCO.2014.6847522}, owner = {lciti}, timestamp = {2015.01.22} }  @inproceedings{Yoshida2007RecordingExperienceLIFEs, title = {Recording experience with the thin-film Longitudinal Intra-Fascicular Electrode, a multichannel peripheral nerve interface}, author = {Yoshida, K. and Kurstjens, M. and Citi, L. and Koch, K.P. and Micera, S.}, booktitle = {Proceedings of the 10th IEEE International Conference on Rehabilitation Robotics ICORR}, year = {2007}, address = {Noordwijk}, month = jun, pages = {862--867}, abstract = {This paper presents our experience evaluating a multi-channel peripheral nerve interface, the thin-film longitudinal intra-fascicular electrode (tfLIFE). One application for the tfLIFE is their potential use as a means to detect independent channels of volitional commands from the amputee. The neural interface would be required to be sufficiently selective to detect the activity of single motor nerve fibres within the nerve stump. Experiments were conducted in the acute rabbit model evaluate the recording characteristics of the tfLIFE array. Multiunit activity was recorded in response to mechanical stimulation of peripheral mechanoreceptors. In some channels in all experiments, large single unit spikes were clearly visible. These data were then processed to determine whether an artificial discriminator could be trained to detect and track activity from the multi unit recordings. We also tested whether inclusion of multi channel information could be used to improve the performance of the discriminator. Our preliminary results indicate the inclusion of multiple channels significantly improves the performance.}, check = {2010.10.27}, doi = {10.1109/ICORR.2007.4428525}, keywords = {biomedical electrodes, discriminators, mechanoception, neuromuscular stimulation, prosthetics, thin film devices, acute rabbit model, amputee, artificial discriminator, mechanical stimulation, multichannel peripheral nerve interface, peripheral mechanoreceptors, single motor nerve fibres, thin-film longitudinal intra-fascicular electrode, volitional commands}, owner = {lciti}, timestamp = {2008.09.07} }  @inproceedings{Barbieri20151037, author = {Barbieri, R. and Valenza, G. and Citi, L. and Placidi, F. and Izzi, F. and Albanese, M. and Marciani, M.G. and Guerrisi, M. and Romigi, A. and Toschi, N.}, title = {Lower instantaneous entropy of heartbeat dynamics during seizures in untreated temporal lobe epilepsy}, booktitle = {Proceedings of Computing in Cardiology}, year = {2015}, volume = {42}, pages = {1037-1040}, abstract = {Temporal lobe epilepsy (TLE) is associated with dysfunction of the autonomic nervous system. While it is known that heart rate variability (HRV) changes in epilepsy comprise both ictal (CRI) and interictal (INT) autonomic cardiac effects, the mechanisms leading to these alterations are not well understood. In this paper we investigate the alterations in instantaneous autonomic complexity during CRI in untreated TLE using bipolar ECG recordings from 10 patients with at least one seizure originating from temporal regions as recorded by video-EEG monitoring. We isolated artifact-free INT and CRI periods and computed mean values of instantaneous point-process Approximate and Sample Entropy (ipApEn and ipSampEn, respectively). ipApEn was significantly lower (p<0.02) and ipSampEn was lower (p<0.065) in CRI vs. INT. The variability (median absolute deviation) of ipApEn was also significantly lower (p<0.03) in CRI vs INT. Our results suggest that ictal events in untreated TLE are associated with a decrease in heartbeat complexity and its variability, possibly pointing toward subtle autonomic changes which may accompany or precede seizures, and can only be detected using an instantaneous, time resolved approach to quantifying autonomic complexity. © 2015 CCAL.}, doi = {10.1109/CIC.2015.7411091} }  @inproceedings{Toschi2017366, author = {Toschi, N. and Valenza, G. and Citi, L. and Guerrisi, M. and Orsolini, S. and Tessa, C. and Diciotti, S. and Barbieri, R.}, title = {Assessment of instantaneous heartbeat dynamics in amnestic mild cognitive impairment}, booktitle = {IFMBE Proceedings}, year = {2017}, volume = {65}, pages = {366-369}, abstract = {In this study, we employ a time-varying, probabilistic model of linear and nonlinear heartbeat dynamics to investigate the possibility of detecting subtle autonomic alterations in subjects suffering from amnestic mild cognitive impairment (aMCI) by exploiting heartbeat information alone. aMCI is a frequent form of cognitive dysfunction which increases the risk of culminating in Alzheimer's disease (AD)-related dementia, and previous studies have demonstrated that AD is accompanied by alterations in autonomic function, which in turn have been linked to cognitive performance in non-demented subjects. We compare 13 MCI patients without ouvert dysautonomia to 13 age- and gender-matched healthy controls by feeding an autonomic nervous system-related linear and nonlinear feature set into a classification framework. Our results show a satisfactory classification performance (73% balanced accuracy), which dropped to 65% when excluding cardiovascular nonlinear/complex features. This outcome confirms the presence of subtle autonomic dysfunction in aMCI (a possible prodromal condition to AD), which can only be detected through to the use of our comprehensive modeling strategy which comprises time-varying, nonlinear/complex estimates of heartbeat dynamics. © Springer Nature Singapore Pte Ltd. 2018.}, doi = {10.1007/978-981-10-5122-7_92} }  @inproceedings{Valenza2016932, author = {Valenza, G. and Citi, L. and Barbieri, R.}, title = {Disentanglement of sympathetic and parasympathetic activity by instantaneous analysis of human heartbeat dynamics}, booktitle = {Proceedings of the 38th {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2016}, pages = {932-935}, abstract = {Spectral analysis of heart rate variability (HRV) is one of the most effective techniques for the assessment of the influence of the autonomic nervous system (ANS) on the heartbeat. Despite its widespread use, it has been demonstrated that HRV subdivision in the low frequency (LF) and high frequency (HF) bands does not accurately reflect separate sympathetic and parasympathetic influences, respectively, mainly due to overlap of the two branches in the low frequencies. Here we propose two novel indices, namely the instantaneous sympathetic autonomic index (SAI) and parasympathetic autonomic index (PAI), that are able to separately assess the time-varying ANS synergic functions. The application of the paradigm is presented here by associating proper combinations of orthonormal Laguerre functions defined within the heartbeat point-process continuous model. Preliminary results from ten subjects recorded during a tilt-table protocol show that the proposed methodology, differently than the traditional spectral parameters, is able to separately track the independent changes associated with the two ANS branches. © 2016 IEEE.}, doi = {10.1109/EMBC.2016.7590854} }  @inproceedings{Greco2017398, author = {Greco, A. and Guidi, A. and Felici, F. and Leo, A. and Ricciardi, E. and Bianchi, M. and Bicchi, A. and Citi, L. and Valenza, G. and Scilingo, E.P.}, title = {Muscle fatigue assessment through electrodermal activity analysis during isometric contraction}, booktitle = {Proceedings of the 39th {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2017}, pages = {398-401}, abstract = {We studied the effects of muscle fatigue on the Autonomic Nervous System (ANS) dynamics. Specifically, we monitored the electrodermal activity (EDA) on 32 healthy subjects performing isometric biceps contraction. As assessed by means of an electromyography (EMG) analysis, 15 subjects showed muscle fatigue and 17 did not. EDA signals were analyzed using the recently proposed cvxEDA model in order to decompose them into their phasic and tonic components and extract effective features to study ANS dynamics. A statistical comparison between the two groups of subjects was performed. Results revealed that relevant phasic EDA features significantly increased in the fatigued group. Moreover, a pattern recognition system was applied to the EDA dataset in order to automatically discriminate between fatigued and non-fatigued subjects. The proposed leave-one-subject-out KNN classifier showed an accuracy of 75.69%. These results suggest the use of EDA as correlate of muscle fatigue, providing integrative information to the standard indices extracted from the EMG signals. © 2017 IEEE.}, doi = {10.1109/EMBC.2017.8036846} }  @inproceedings{Valenza2016985, author = {Valenza, G. and Romigi, A. and Citi, L. and Placidi, F. and Izzi, F. and Albanese, M. and Scilingo, E.P. and Marciani, M.G. and Duggento, A. and Guerrisi, M. and Toschi, N. and Barbieri, R.}, title = {Predicting seizures in untreated temporal lobe epilepsy using point-process nonlinear models of heartbeat dynamics}, booktitle = {Proceedings of the 38th {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2016}, volume = {2016-October}, pages = {985-988}, abstract = {Symptoms of temporal lobe epilepsy (TLE) are frequently associated with autonomic dysregulation, whose underlying biological processes are thought to strongly contribute to sudden unexpected death in epilepsy (SUDEP). While abnormal cardiovascular patterns commonly occur during ictal events, putative patterns of autonomic cardiac effects during pre-ictal (PRE) periods (i.e. periods preceding seizures) are still unknown. In this study, we investigated TLE-related heart rate variability (HRV) through instantaneous, nonlinear estimates of cardiovascular oscillations during inter-ictal (INT) and PRE periods. ECG recordings from 12 patients with TLE were processed to extract standard HRV indices, as well as indices of instantaneous HRV complexity (dominant Lyapunov exponent and entropy) and higher-order statistics (bispectra) obtained through definition of inhomogeneous point-process nonlinear models, employing Volterra-Laguerre expansions of linear, quadratic, and cubic kernels. Experimental results demonstrate that the best INT vs. PRE classification performance (balanced accuracy: 73.91%) was achieved only when retaining the time-varying, nonlinear, and non-stationary structure of heartbeat dynamical features. The proposed approach opens novel important avenues in predicting ictal events using information gathered from cardiovascular signals exclusively. © 2016 IEEE.}, doi = {10.1109/EMBC.2016.7590867} }  @inproceedings{Li2017SelfReportedWellBeingScoreModelling, author = {Li, X. and Poli, R. and Valenza, G. and Scilingo, E.P. and Citi, L.}, title = {Self-reported well-being score modelling and prediction: Proof-of-concept of an approach based on linear dynamic systems}, booktitle = {Proceedings of the 39th {IEEE} Engineering in Medicine and Biology Society Conference, {EMBC}}, year = {2017}, pages = {2205-2208}, abstract = {Assessment and recognition of perceived well-being has wide applications in the development of assistive healthcare systems for people with physical and mental disorders. In practical data collection, these systems need to be less intrusive, and respect users' autonomy and willingness as much as possible. As a result, self-reported data are not necessarily available at all times. Conventional classifiers, which usually require feature vectors of a prefixed dimension, are not well suited for this problem. To address the issue of non-uniformly sampled measurements, in this study we propose a method for the modelling and prediction of self-reported well-being scores based on a linear dynamic system. Within the model, we formulate different features as observations, making predictions even in the presence of inconsistent and irregular data. We evaluate the proposed method with synthetic data, as well as real data from two patients diagnosed with cancer. In the latter, self-reported scores from three well-being-related scales were collected over a period of approximately 60 days. Prompted each day, the patients had the choice whether to respond or not. Results show that the proposed model is able to track and predict the patients' perceived well-being dynamics despite the irregularly sampled data. © 2017 IEEE.}, doi = {10.1109/EMBC.2017.8037292} }  @comment{{jabref-meta: databaseType:bibtex;}}  @phdthesis{LCitiPhd, title = {Development of a neural interface for the control of a robotic hand}, author = {Luca Citi}, school = {IMT Lucca and Scuola Superiore Sant'Anna Pisa}, year = {2009}, month = apr, abstract = {The restoration of sensorimotor functions for the control ofartificial hands is a fundamental point in order to improve the quality of life of amputees. Current hand prostheses use electromyographic (EMG) signals, but are limited to a small number of channels and rely on visual feedback. As the interface is the bottleneck for a wide class of hybrid bionic systems, we have developed a general framework to match task requirements with interface performance. We have carefully and thoroughly examined the case of the amputee user and its requirements: throughput and latency, but also user-friendliness, invasiveness, bi-directionality, and possibility of natural control of the prosthesis. From this analysis, we have concluded that, albeit suboptimal from a mere throughput and latency point of view, peripheral invasive interface can represent a promising medium-term solution. We have compared the different types of interfaces with the peripheral nervous system, finding in longitudinal intra-fascicular interfaces (LIFEs) a tradeoff between invasiveness and selectivity. In order to assess the possibility of extracting complex information from LIFEs, we have run preliminary experiments with small animal models recording induced afferent information. Using the sophisticated signal processing techniques developed (wavelet denoising and spike sorting) and a robust classifier, we were able to discriminate four (or five) different classes of stimuli with performance in a range between 90\% and 99\%. These results confirmed and outperformed prior work carried out with different approaches. There are plans to validate the approach with a human amputee. Hence, several steps have been taken in order to make possible the recording of neural signals from a human subject and allow online processing and control of the Cyberhand'' smart robotic hand prosthesis.}, check = {2010.10.27}, owner = {lciti}, timestamp = {2010.10.28}, url = {http://users.neurostat.mit.edu/lciti/publications_files/LCitiPhD.pdf} }  @mastersthesis{LCitiMSThesis, title = {Un'interfaccia cervello-computer mediante metodi evoluzionistici di trattamento di segnali {EEG}}, author = {Luca Citi}, school = {Universit\a degli Studi di Firenze}, year = {2004}, month = jul, check = {2010.10.27}, owner = {lciti}, timestamp = {2010.10.28}, url = {http://users.neurostat.mit.edu/lciti/publications_files/LCitiMSThesis.pdf} }  @comment{{jabref-meta: databaseType:bibtex;}} `