Thomas Hoellinger | Université libre de Bruxelles (original) (raw)

Papers by Thomas Hoellinger

Research paper thumbnail of Brain Oscillations in Sport: Toward EEG Biomarkers of Performance

Brain dynamics is at the basis of top performance accomplishment in sports. The search for neural... more Brain dynamics is at the basis of top performance accomplishment in sports. The search for neural biomarkers of performance remains a challenge in movement science and sport psychology. The non-invasive nature of high-density electroencephalography (EEG) recording has made it a most promising avenue for providing quantitative feedback to practitioners and coaches. Here, we review the current relevance of the main types of EEG oscillations in order to trace a perspective for future practical applications of EEG and event-related potentials (ERP) in sport. In this context, the hypotheses of unified brain rhythms and continuity between wake and sleep states should provide a functional template for EEG biomarkers in sport. The oscillations in the thalamo-cortical and hippocampal circuitry including the physiology of the place cells and the grid cells provide a frame of reference for the analysis of delta, theta, beta, alpha (incl.mu), and gamma oscillations recorded in the space field of human performance. Based on recent neuronal models facilitating the distinction between the different dynamic regimes (selective gating and binding) in these different oscillations we suggest an integrated approach articulating together the classical biomechanical factors (3D movements and EMG) and the high-density EEG and ERP signals to allow finer mathematical analysis to optimize sport performance, such as microstates, coherency/directionality analysis and neural generators.

Research paper thumbnail of Design and Control of the MINDWALKER Exoskeleton

IEEE transactions on neural systems and rehabilitation engineering : a publication of the IEEE Engineering in Medicine and Biology Society, Jan 30, 2014

Powered exoskeletons can empower paraplegics to stand and walk. Actively controlled hip ab/adduct... more Powered exoskeletons can empower paraplegics to stand and walk. Actively controlled hip ab/adduction (HAA) is needed for weight shift and for lateral foot placement to support dynamic balance control and to counteract disturbances in the frontal plane. Here, we describe the design, control, and preliminary evaluation of a novel exoskeleton, MINDWALKER. Besides powered hip flexion/ extension and knee flexion/extension, it also has powered HAA. Each of the powered joints has a series elastic actuator, which can deliver 100Nm torque and 1kW power. A finite-state machine based controller provides gait assistance in both the sagittal and frontal planes. State transitions, such as stepping, can be triggered by the displacement of the Center of Mass (CoM). A novel step-width adaptation algorithm was proposed to stabilize lateral balance. We tested this exoskeleton on both healthy subjects and paraplegics. Experimental results showed that all users could successfully trigger steps by CoM di...

Research paper thumbnail of Oscillations in the human brain during walking execution, imagination and observation

Neuropsychologia

Gait is an essential human activity which organizes many functional and cognitive behaviors. The ... more Gait is an essential human activity which organizes many functional and cognitive behaviors. The biomechanical constraints of bipedalism implicating a permanent control of balance during gait are taken into account by a complex dialog between the cortical, subcortical and spinal networks. This networking is largely based on oscillatory coding, including changes in spectral power and phase-locking of ongoing neural activity in theta, alpha, beta and gamma frequency bands. This coding is specifically modulated in actual gait execution and representation, as well as in contexts of gait observation or imagination. A main challenge in integrative neuroscience oscillatory activity analysis is to disentangle the brain oscillations devoted to gait control. In addition to neuroimaging approaches, which have highlighted the structural components of an extended network, dynamic high-density EEG gives non-invasive access to functioning of this network. Here we revisit the neurophysiological foundations of behavior-related EEG in the light of current neuropsychological theoretic frameworks. We review different EEG rhythms emerging in the most informative paradigms relating to human gait and implications for rehabilitation strategies.

Research paper thumbnail of Kinematics of lifting objects with unexpected weights in healthy subjects and a deafferented patient

Page 1. 1 Kinematics of lifting objects with unexpected weights in healthy subjects and a deaffer... more Page 1. 1 Kinematics of lifting objects with unexpected weights in healthy subjects and a deafferented patient. Thomas Hoellinger 1-2 , Joe McIntyre 3 , Sylvain Hanneton 1-2 , Lena Jami 1-2 , Agnes Roby-Brami 1-2 . 1: Paris ...

Research paper thumbnail of Microstates in ADHD children during a visual cued GO/NOGO task

Children with attention deficit/hyperactivity disorder (ADHD) have been found to show theta-beta ... more Children with attention deficit/hyperactivity disorder (ADHD) have been found to show theta-beta correlation in rhythmic brain oscillations. We aimed to further analyse scalp activity in order to study global amplitude of activation and topographical stability during a visual-cued task in children with ADHD. Participants and methods: Fourteen ADHD and 14 aged-matched control children underwent EEG while performing a visual-cued GO-NOGO task. We performed theta-beta corroboration, topographical activation study, including global field potential (GFP) and transiently stable brain states (microstates). We performed a topographical ANOVA to establish differences between conditions and other statistical analysis (comprising unpaired t-tests) to fit maps within subject. Results: ADHD children had significantly smaller amplitude at first and third peak and larger second peak in the W-shaped GFP after CUE, GO and NOGO visual onsets than control children, who showed the reverse image to this...

Research paper thumbnail of Etude du couplage audio-moteur chez des sujets valides par un système de capture du mouvement électromagnétique

ABSTRACT Les systèmes de capture électromagnétique permettent d'enregistrer des positions... more ABSTRACT Les systèmes de capture électromagnétique permettent d'enregistrer des positions et des orientations dans l'espace tridimensionnel au cours du temps. Nous avons développé un système de réalité virtuelle purement auditif couplant les mouvements de la main et de la tête à un générateur sonore tridimensionnel (OpenAl). Lors de l'expérience, le but du sujet est d'attraper une source sonore fixe. Le son est perçu par des « oreilles virtuelles » placées soit sur la main (mode main) soit sur la tête (mode tête). Les variations sonores perçues par le sujet sont sensibles à la position et l'orientation des « oreilles virtuelles ». Les résultats préliminaires montrent que lors de l'expérience en mode main le sujet produit plus de mouvements exploratoires. De plus, le pourcentage de réussite en mode main est plus important qu'en mode tête. La réussite dépend également de la position 3D des cibles : elle est plus grande pour les cibles basses et lointaines en mode main et pour les cibles hautes et proches en mode tête. Cette étude préliminaire a permis de démontrer dans un premier temps la faisabilité de ce type de protocole. La réussite semble dépendre de la capacité à explorer l'espace c'est à dire à améliorer ses entrées sensorielles. Dans cette étude la capture et l'analyse du mouvement sont appliquées à l'enrichissement de l'environnement d'action dans le cadre de la rééducation.

Research paper thumbnail of Direct kinematic modeling of the upper limb during trunk-assisted reaching

Journal of applied biomechanics, 2011

The study proposes a rigid-body biomechanical model of the trunk and whole upper limb including s... more The study proposes a rigid-body biomechanical model of the trunk and whole upper limb including scapula and the test of this model with a kinematic method using a six-dimensional (6-D) electromagnetic motion capture (mocap) device. Large unconstrained natural trunk-assisted reaching movements were recorded in 7 healthy subjects. The 3-D positions of anatomical landmarks were measured and then compared to their estimation given by the biomechanical chain fed with joint angles (the direct kinematics). Thus, the prediction errors was attributed to the different joints and to the different simplifications introduced in the model. Large (approx. 4 cm) end-point prediction errors at the level of the hand were reduced (to approx. 2 cm) if translations of the scapula were taken into account. As a whole, the 6-D mocap seems to give accurate results, except for prono-supination. The direct kinematic model could be used as a virtual mannequin for other applications, such as computer animation ...

Research paper thumbnail of A subjective assessment of a P300 BCI system for lower-limb rehabilitation purposes

Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2012

Recent research has shown that a P300 system can be used while walking without requiring any spec... more Recent research has shown that a P300 system can be used while walking without requiring any specific gait-related artifact removal techniques. Also, standard EEG-based Brain-Computer Interfaces (BCI) have not been really assessed for lower limb rehabilitation/prosthesis. Therefore, this paper gives a first baseline estimation (for future BCI comparisons) of the subjective and objective performances of a four-state P300 BCI plus a non-control state for lower-limb rehabilitation purposes. To assess usability and workload, the System Usability Scale and the NASA Task Load Index questionnaires were administered to five healthy subjects after performing a real-time treadmill speed control. Results show that the P300 BCI approach could suit fitness and rehabilitation applications, whereas prosthesis control, which suffers from a low reactivity, appears too sensitive for risky and crowded areas.

Research paper thumbnail of Human Walk Modeled by PCPG to Control a Lower Limb Neuroprosthesis by High-Level Commands

Research paper thumbnail of From Spinal Central Pattern Generators to Cortical Network: Integrated BCI for Walking Rehabilitation

Neural Plasticity, 2012

Success in locomotor rehabilitation programs can be improved with the use of brain-computer inter... more Success in locomotor rehabilitation programs can be improved with the use of brain-computer interfaces (BCIs). Although a wealth of research has demonstrated that locomotion is largely controlled by spinal mechanisms, the brain is of utmost importance in monitoring locomotor patterns and therefore contains information regarding central pattern generation functioning. In addition, there is also a tight coordination between the upper and lower limbs, which can also be useful in controlling locomotion. The current paper critically investigates different approaches that are applicable to this field: the use of electroencephalogram (EEG), upper limb electromyogram (EMG), or a hybrid of the two neurophysiological signals to control assistive exoskeletons used in locomotion based on programmable central pattern generators (PCPGs) or dynamic recurrent neural networks (DRNNs). Plantar surface tactile stimulation devices combined with virtual reality may provide the sensation of walking while in a supine position for use of training brain signals generated during locomotion. These methods may exploit mechanisms of brain plasticity and assist in the neurorehabilitation of gait in a variety of clinical conditions, including stroke, spinal trauma, multiple sclerosis, and cerebral palsy.

Research paper thumbnail of A quantitative comparison of the most sophisticated EOG-based eye movement recognition techniques

2013 IEEE Symposium on Computational Intelligence, Cognitive Algorithms, Mind, and Brain (CCMB), 2013

DI-fusion, le Dépôt institutionnel numérique de l'ULB, est l'ou... more DI-fusion, le Dépôt institutionnel numérique de l'ULB, est l'outil de référencementde la production scientifique de l'ULB.L'interface de recherche DI-fusion permet de consulter les publications des chercheurs de l'ULB et les thèses qui y ont été défendues.

Research paper thumbnail of MINDWALKER: Going one step further with assistive lower limbs exoskeleton for SCI condition subjects

2012 4th IEEE RAS & EMBS International Conference on Biomedical Robotics and Biomechatronics (BioRob), 2012

This paper presents MINDWALKER, which is an ambitious EC funded research project coordinated by S... more This paper presents MINDWALKER, which is an ambitious EC funded research project coordinated by Space Applications Services aiming at the development of novel Brain Neural Computer Interfaces (BNCI) and robotics technologies, with the goal of obtaining a crutch-less assistive lower limbs exoskeleton, with non-invasive brain control approach as main strategy. Complementary BNCI control approaches such as arms electromyograms (EMG) are also researched. In the last phase of the project, the developed system should undergo a clinical evaluation with Spinal Cord Injured (SCI) subjects at the Fondazione

Research paper thumbnail of EMG patterns during assisted walking in the exoskeleton

Frontiers in Human Neuroscience, 2014

Research paper thumbnail of Neural rhythmic symphony of human walking observation: Upside-down and Uncoordinated condition on cortical theta, alpha, beta and gamma oscillations

Frontiers in Systems Neuroscience, 2014

Biological motion observation has been recognized to produce dynamic change in sensorimotor activ... more Biological motion observation has been recognized to produce dynamic change in sensorimotor activation according to the observed kinematics. Physical plausibility of the spatial-kinematic relationship of human movement may play a major role in the top-down processing of human motion recognition. Here, we investigated the time course of scalp activation during observation of human gait in order to extract and use it on future integrated brain-computer interface using virtual reality (VR). We analyzed event related potentials (ERP), the event related spectral perturbation (ERSP) and the inter-trial coherence (ITC) from high-density EEG recording during video display onset (−200-600 ms) and the steady state visual evoked potentials (SSVEP) inside the video of human walking 3D-animation in three conditions: Normal; Upside-down (inverted images); and Uncoordinated (pseudo-randomly mixed images). We found that early visual evoked response P120 was decreased in Upside-down condition. The N170 and P300b amplitudes were decreased in Uncoordinated condition. In Upside-down and Uncoordinated conditions, we found decreased alpha power and theta phase-locking. As regards gamma oscillation, power was increased during the Upside-down animation and decreased during the Uncoordinated animation. An SSVEP-like response oscillating at about 10 Hz was also described showing that the oscillating pattern is enhanced 300 ms after the heel strike event only in the Normal but not in the Upside-down condition. Our results are consistent with most of previous point-light display studies, further supporting possible use of virtual reality for neurofeedback applications.

Research paper thumbnail of Physiological modules for generating discrete and rhythmic movements: action identification by a dynamic recurrent neural network

Frontiers in Computational Neuroscience, 2014

A central question in Neuroscience is that of how the nervous system generates the spatiotemporal... more A central question in Neuroscience is that of how the nervous system generates the spatiotemporal commands needed to realize complex gestures, such as handwriting. A key postulate is that the central nervous system (CNS) builds up complex movements from a set of simpler motor primitives or control modules. In this study we examined the control modules underlying the generation of muscle activations when performing different types of movement: discrete, point-to-point movements in eight different directions and continuous figure-eight movements in both the normal, upright orientation and rotated 90 • . To test for the effects of biomechanical constraints, movements were performed in the frontal-parallel or sagittal planes, corresponding to two different nominal flexion/abduction postures of the shoulder. In all cases we measured limb kinematics and surface electromyographic activity (EMG) signals for seven different muscles acting around the shoulder. We first performed principal component analysis (PCA) of the EMG signals on a movement-by-movement basis. We found a surprisingly consistent pattern of muscle groupings across movement types and movement planes, although we could detect systematic differences between the PCs derived from movements performed in each shoulder posture and between the principal components associated with the different orientations of the figure. Unexpectedly we found no systematic differences between the figure eights and the point-to-point movements. The first three principal components could be associated with a general co-contraction of all seven muscles plus two patterns of reciprocal activation. From these results, we surmise that both "discreterhythmic movements" such as the figure eight, and discrete point-to-point movement may be constructed from three different fundamental modules, one regulating the impedance of the limb over the time span of the movement and two others operating to generate movement, one aligned with the vertical and the other aligned with the horizontal.

Research paper thumbnail of A five-state P300-based foot lifter orthosis: Proof of concept

2012 ISSNIP Biosignals and Biorobotics Conference: Biosignals and Robotics for Better and Safer Living (BRC), 2012

Current lower limb prostheses do not integrate recent developments in robotics and in Brain-Compu... more Current lower limb prostheses do not integrate recent developments in robotics and in Brain-Computer Interfaces (BCIs). In fact, active lower limb prostheses seldom consider the user's intent, they often determine the correct movement from those of healthy parts of the body or from the residual limb. Recently, an emerging idea for non-invasive BCIs was proposed to allow such low bitrate systems to control a lower limb prosthesis thanks to a Central Pattern Generator (CPG) widely used in robotics. This CPG allows to automatically generate a periodic gait pattern. Furthermore, the CPG pattern frequency and magnitude can be adapted according to the specific gait behavior of the patient and his desired speed. This paper proves the concept of combining a human gait model based on a CPG and a classic but non-natural P300 BCI in order to consider the user's intent. The details of how the entire chain can be practically implemented are given. Finally, preliminary results on four healthy subjects for a four-speed P300-based lower limb orthosis with a non-control state are presented. Globally, results are satisfying and prove the feasibility of such systems.

Research paper thumbnail of Optimizing the Performances of a P300-Based Brain–Computer Interface in Ambulatory Conditions

IEEE Journal on Emerging and Selected Topics in Circuits and Systems, 2011

Brain-computer interfaces (BCIs) enable their users to interact with their surrounding environmen... more Brain-computer interfaces (BCIs) enable their users to interact with their surrounding environment using the activity of their brain only, without activating any muscle. This technology provides severely disabled people with an alternative mean to communicate or control any electric device. On the other hand, BCI applications are more and more dedicated to healthier people, with the aim of giving them access to augmented reality or new rehabilitation tools. As it is noninvasive, light and relatively cheap, electroencephalography (EEG) is the most used acquisition technique to record cerebral activity of the BCI users. However, when using such type of BCI, user movements are likely to provoke motions of the measuring electrodes which can severely damage the EEG quality. Thus, current BCI technology requires that the user sits and performs as little movements as possible. This is of course a strong limitation of BCI for use in ordinary life. Very recently, preliminary studies have been published in the literature and suggest that BCI applications can be realized even in the physically moving context. In this paper, we thoroughly investigate the possibility to develop a P300-based BCI system in ambulatory condition. The study is based on experimental data recorded with seven subjects executing a visual P300 speller-like discrimination task while simultaneously walking at different speeds on a treadmill. It is demonstrated that a P300-based BCI is definitely feasible in such conditions. Different artifact correction methods are described and discussed in detail. To conclude, a recommended approach is given for the development of a real-time application.

Research paper thumbnail of Physiological modules for generating discrete and rhythmic movements: component analysis of EMG signals

Frontiers in Computational Neuroscience, 2015

A central question in Neuroscience is that of how the nervous system generates the spatiotemporal... more A central question in Neuroscience is that of how the nervous system generates the spatiotemporal commands needed to realize complex gestures, such as handwriting. A key postulate is that the central nervous system (CNS) builds up complex movements from a set of simpler motor primitives or control modules. In this study we examined the control modules underlying the generation of muscle activations when performing different types of movement: discrete, point-to-point movements in eight different directions and continuous figure-eight movements in both the normal, upright orientation and rotated 90 • . To test for the effects of biomechanical constraints, movements were performed in the frontal-parallel or sagittal planes, corresponding to two different nominal flexion/abduction postures of the shoulder. In all cases we measured limb kinematics and surface electromyographic activity (EMG) signals for seven different muscles acting around the shoulder. We first performed principal component analysis (PCA) of the EMG signals on a movement-by-movement basis. We found a surprisingly consistent pattern of muscle groupings across movement types and movement planes, although we could detect systematic differences between the PCs derived from movements performed in each shoulder posture and between the principal components associated with the different orientations of the figure. Unexpectedly we found no systematic differences between the figure eights and the point-to-point movements. The first three principal components could be associated with a general co-contraction of all seven muscles plus two patterns of reciprocal activation. From these results, we surmise that both "discreterhythmic movements" such as the figure eight, and discrete point-to-point movement may be constructed from three different fundamental modules, one regulating the impedance of the limb over the time span of the movement and two others operating to generate movement, one aligned with the vertical and the other aligned with the horizontal.

Research paper thumbnail of Control of Leg Movements Driven by EMG Activity of Shoulder Muscles

Frontiers in Human Neuroscience, 2014

During human walking, there exists a functional neural coupling between arms and legs, and betwee... more During human walking, there exists a functional neural coupling between arms and legs, and between cervical and lumbosacral pattern generators. Here, we present a novel approach for associating the electromyographic (EMG) activity from upper limb muscles with leg kinematics. Our methodology takes advantage of the high involvement of shoulder muscles in most locomotor-related movements and of the natural co-ordination between arms and legs. Nine healthy subjects were asked to walk at different constant and variable speeds (3-5 km/h), while EMG activity of shoulder (deltoid) muscles and the kinematics of walking were recorded. To ensure a high level of EMG activity in deltoid, the subjects performed slightly larger arm swinging than they usually do. The temporal structure of the burst-like EMG activity was used to predict the spatiotemporal kinematic pattern of the forthcoming step. A comparison of actual and predicted stride leg kinematics showed a high degree of correspondence (r > 0.9). This algorithm has been also implemented in pilot experiments for controlling avatar walking in a virtual reality setup and an exoskeleton during over-ground stepping. The proposed approach may have important implications for the design of human-machine interfaces and neuroprosthetic technologies such as those of assistive lower limb exoskeletons.

Research paper thumbnail of An analysis of EEG signals during voluntary rhythmic foot movements

2011 5th International IEEE/EMBS Conference on Neural Engineering, 2011

Human locomotion is based on complex interactions of several cortical and subcortical structures.... more Human locomotion is based on complex interactions of several cortical and subcortical structures. Over the years, the main underlying mechanisms have been partially unveiled thanks to standard functional neuroimaging techniques as well as electroencephalography (EEG). However, a complete picture is still lacking to date, due to particularly challenging experimental difficulties arising on top of the inherent complexity of the involved mechanisms. In this context, the aim of this study was to investigate the EEG dynamics associated to the production of voluntary rhythmic foot movements only. We used an experimental protocol limiting drastically the presence of movement artifacts in the EEG signals compared to real walk on a treadmill. A time-frequency analysis was performed, based on a time-warping method allowing an ensemble averaging of the data of 3 subjects. Characteristic alternation of power increases and decreases in the alpha, beta and gamma bands during the movement cycle is demonstrated as well as the emergence of two different neural coordination schemes related to in-phase and anti-phase foot movements.

Research paper thumbnail of Brain Oscillations in Sport: Toward EEG Biomarkers of Performance

Brain dynamics is at the basis of top performance accomplishment in sports. The search for neural... more Brain dynamics is at the basis of top performance accomplishment in sports. The search for neural biomarkers of performance remains a challenge in movement science and sport psychology. The non-invasive nature of high-density electroencephalography (EEG) recording has made it a most promising avenue for providing quantitative feedback to practitioners and coaches. Here, we review the current relevance of the main types of EEG oscillations in order to trace a perspective for future practical applications of EEG and event-related potentials (ERP) in sport. In this context, the hypotheses of unified brain rhythms and continuity between wake and sleep states should provide a functional template for EEG biomarkers in sport. The oscillations in the thalamo-cortical and hippocampal circuitry including the physiology of the place cells and the grid cells provide a frame of reference for the analysis of delta, theta, beta, alpha (incl.mu), and gamma oscillations recorded in the space field of human performance. Based on recent neuronal models facilitating the distinction between the different dynamic regimes (selective gating and binding) in these different oscillations we suggest an integrated approach articulating together the classical biomechanical factors (3D movements and EMG) and the high-density EEG and ERP signals to allow finer mathematical analysis to optimize sport performance, such as microstates, coherency/directionality analysis and neural generators.

Research paper thumbnail of Design and Control of the MINDWALKER Exoskeleton

IEEE transactions on neural systems and rehabilitation engineering : a publication of the IEEE Engineering in Medicine and Biology Society, Jan 30, 2014

Powered exoskeletons can empower paraplegics to stand and walk. Actively controlled hip ab/adduct... more Powered exoskeletons can empower paraplegics to stand and walk. Actively controlled hip ab/adduction (HAA) is needed for weight shift and for lateral foot placement to support dynamic balance control and to counteract disturbances in the frontal plane. Here, we describe the design, control, and preliminary evaluation of a novel exoskeleton, MINDWALKER. Besides powered hip flexion/ extension and knee flexion/extension, it also has powered HAA. Each of the powered joints has a series elastic actuator, which can deliver 100Nm torque and 1kW power. A finite-state machine based controller provides gait assistance in both the sagittal and frontal planes. State transitions, such as stepping, can be triggered by the displacement of the Center of Mass (CoM). A novel step-width adaptation algorithm was proposed to stabilize lateral balance. We tested this exoskeleton on both healthy subjects and paraplegics. Experimental results showed that all users could successfully trigger steps by CoM di...

Research paper thumbnail of Oscillations in the human brain during walking execution, imagination and observation

Neuropsychologia

Gait is an essential human activity which organizes many functional and cognitive behaviors. The ... more Gait is an essential human activity which organizes many functional and cognitive behaviors. The biomechanical constraints of bipedalism implicating a permanent control of balance during gait are taken into account by a complex dialog between the cortical, subcortical and spinal networks. This networking is largely based on oscillatory coding, including changes in spectral power and phase-locking of ongoing neural activity in theta, alpha, beta and gamma frequency bands. This coding is specifically modulated in actual gait execution and representation, as well as in contexts of gait observation or imagination. A main challenge in integrative neuroscience oscillatory activity analysis is to disentangle the brain oscillations devoted to gait control. In addition to neuroimaging approaches, which have highlighted the structural components of an extended network, dynamic high-density EEG gives non-invasive access to functioning of this network. Here we revisit the neurophysiological foundations of behavior-related EEG in the light of current neuropsychological theoretic frameworks. We review different EEG rhythms emerging in the most informative paradigms relating to human gait and implications for rehabilitation strategies.

Research paper thumbnail of Kinematics of lifting objects with unexpected weights in healthy subjects and a deafferented patient

Page 1. 1 Kinematics of lifting objects with unexpected weights in healthy subjects and a deaffer... more Page 1. 1 Kinematics of lifting objects with unexpected weights in healthy subjects and a deafferented patient. Thomas Hoellinger 1-2 , Joe McIntyre 3 , Sylvain Hanneton 1-2 , Lena Jami 1-2 , Agnes Roby-Brami 1-2 . 1: Paris ...

Research paper thumbnail of Microstates in ADHD children during a visual cued GO/NOGO task

Children with attention deficit/hyperactivity disorder (ADHD) have been found to show theta-beta ... more Children with attention deficit/hyperactivity disorder (ADHD) have been found to show theta-beta correlation in rhythmic brain oscillations. We aimed to further analyse scalp activity in order to study global amplitude of activation and topographical stability during a visual-cued task in children with ADHD. Participants and methods: Fourteen ADHD and 14 aged-matched control children underwent EEG while performing a visual-cued GO-NOGO task. We performed theta-beta corroboration, topographical activation study, including global field potential (GFP) and transiently stable brain states (microstates). We performed a topographical ANOVA to establish differences between conditions and other statistical analysis (comprising unpaired t-tests) to fit maps within subject. Results: ADHD children had significantly smaller amplitude at first and third peak and larger second peak in the W-shaped GFP after CUE, GO and NOGO visual onsets than control children, who showed the reverse image to this...

Research paper thumbnail of Etude du couplage audio-moteur chez des sujets valides par un système de capture du mouvement électromagnétique

ABSTRACT Les systèmes de capture électromagnétique permettent d'enregistrer des positions... more ABSTRACT Les systèmes de capture électromagnétique permettent d'enregistrer des positions et des orientations dans l'espace tridimensionnel au cours du temps. Nous avons développé un système de réalité virtuelle purement auditif couplant les mouvements de la main et de la tête à un générateur sonore tridimensionnel (OpenAl). Lors de l'expérience, le but du sujet est d'attraper une source sonore fixe. Le son est perçu par des « oreilles virtuelles » placées soit sur la main (mode main) soit sur la tête (mode tête). Les variations sonores perçues par le sujet sont sensibles à la position et l'orientation des « oreilles virtuelles ». Les résultats préliminaires montrent que lors de l'expérience en mode main le sujet produit plus de mouvements exploratoires. De plus, le pourcentage de réussite en mode main est plus important qu'en mode tête. La réussite dépend également de la position 3D des cibles : elle est plus grande pour les cibles basses et lointaines en mode main et pour les cibles hautes et proches en mode tête. Cette étude préliminaire a permis de démontrer dans un premier temps la faisabilité de ce type de protocole. La réussite semble dépendre de la capacité à explorer l'espace c'est à dire à améliorer ses entrées sensorielles. Dans cette étude la capture et l'analyse du mouvement sont appliquées à l'enrichissement de l'environnement d'action dans le cadre de la rééducation.

Research paper thumbnail of Direct kinematic modeling of the upper limb during trunk-assisted reaching

Journal of applied biomechanics, 2011

The study proposes a rigid-body biomechanical model of the trunk and whole upper limb including s... more The study proposes a rigid-body biomechanical model of the trunk and whole upper limb including scapula and the test of this model with a kinematic method using a six-dimensional (6-D) electromagnetic motion capture (mocap) device. Large unconstrained natural trunk-assisted reaching movements were recorded in 7 healthy subjects. The 3-D positions of anatomical landmarks were measured and then compared to their estimation given by the biomechanical chain fed with joint angles (the direct kinematics). Thus, the prediction errors was attributed to the different joints and to the different simplifications introduced in the model. Large (approx. 4 cm) end-point prediction errors at the level of the hand were reduced (to approx. 2 cm) if translations of the scapula were taken into account. As a whole, the 6-D mocap seems to give accurate results, except for prono-supination. The direct kinematic model could be used as a virtual mannequin for other applications, such as computer animation ...

Research paper thumbnail of A subjective assessment of a P300 BCI system for lower-limb rehabilitation purposes

Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2012

Recent research has shown that a P300 system can be used while walking without requiring any spec... more Recent research has shown that a P300 system can be used while walking without requiring any specific gait-related artifact removal techniques. Also, standard EEG-based Brain-Computer Interfaces (BCI) have not been really assessed for lower limb rehabilitation/prosthesis. Therefore, this paper gives a first baseline estimation (for future BCI comparisons) of the subjective and objective performances of a four-state P300 BCI plus a non-control state for lower-limb rehabilitation purposes. To assess usability and workload, the System Usability Scale and the NASA Task Load Index questionnaires were administered to five healthy subjects after performing a real-time treadmill speed control. Results show that the P300 BCI approach could suit fitness and rehabilitation applications, whereas prosthesis control, which suffers from a low reactivity, appears too sensitive for risky and crowded areas.

Research paper thumbnail of Human Walk Modeled by PCPG to Control a Lower Limb Neuroprosthesis by High-Level Commands

Research paper thumbnail of From Spinal Central Pattern Generators to Cortical Network: Integrated BCI for Walking Rehabilitation

Neural Plasticity, 2012

Success in locomotor rehabilitation programs can be improved with the use of brain-computer inter... more Success in locomotor rehabilitation programs can be improved with the use of brain-computer interfaces (BCIs). Although a wealth of research has demonstrated that locomotion is largely controlled by spinal mechanisms, the brain is of utmost importance in monitoring locomotor patterns and therefore contains information regarding central pattern generation functioning. In addition, there is also a tight coordination between the upper and lower limbs, which can also be useful in controlling locomotion. The current paper critically investigates different approaches that are applicable to this field: the use of electroencephalogram (EEG), upper limb electromyogram (EMG), or a hybrid of the two neurophysiological signals to control assistive exoskeletons used in locomotion based on programmable central pattern generators (PCPGs) or dynamic recurrent neural networks (DRNNs). Plantar surface tactile stimulation devices combined with virtual reality may provide the sensation of walking while in a supine position for use of training brain signals generated during locomotion. These methods may exploit mechanisms of brain plasticity and assist in the neurorehabilitation of gait in a variety of clinical conditions, including stroke, spinal trauma, multiple sclerosis, and cerebral palsy.

Research paper thumbnail of A quantitative comparison of the most sophisticated EOG-based eye movement recognition techniques

2013 IEEE Symposium on Computational Intelligence, Cognitive Algorithms, Mind, and Brain (CCMB), 2013

DI-fusion, le Dépôt institutionnel numérique de l'ULB, est l'ou... more DI-fusion, le Dépôt institutionnel numérique de l'ULB, est l'outil de référencementde la production scientifique de l'ULB.L'interface de recherche DI-fusion permet de consulter les publications des chercheurs de l'ULB et les thèses qui y ont été défendues.

Research paper thumbnail of MINDWALKER: Going one step further with assistive lower limbs exoskeleton for SCI condition subjects

2012 4th IEEE RAS & EMBS International Conference on Biomedical Robotics and Biomechatronics (BioRob), 2012

This paper presents MINDWALKER, which is an ambitious EC funded research project coordinated by S... more This paper presents MINDWALKER, which is an ambitious EC funded research project coordinated by Space Applications Services aiming at the development of novel Brain Neural Computer Interfaces (BNCI) and robotics technologies, with the goal of obtaining a crutch-less assistive lower limbs exoskeleton, with non-invasive brain control approach as main strategy. Complementary BNCI control approaches such as arms electromyograms (EMG) are also researched. In the last phase of the project, the developed system should undergo a clinical evaluation with Spinal Cord Injured (SCI) subjects at the Fondazione

Research paper thumbnail of EMG patterns during assisted walking in the exoskeleton

Frontiers in Human Neuroscience, 2014

Research paper thumbnail of Neural rhythmic symphony of human walking observation: Upside-down and Uncoordinated condition on cortical theta, alpha, beta and gamma oscillations

Frontiers in Systems Neuroscience, 2014

Biological motion observation has been recognized to produce dynamic change in sensorimotor activ... more Biological motion observation has been recognized to produce dynamic change in sensorimotor activation according to the observed kinematics. Physical plausibility of the spatial-kinematic relationship of human movement may play a major role in the top-down processing of human motion recognition. Here, we investigated the time course of scalp activation during observation of human gait in order to extract and use it on future integrated brain-computer interface using virtual reality (VR). We analyzed event related potentials (ERP), the event related spectral perturbation (ERSP) and the inter-trial coherence (ITC) from high-density EEG recording during video display onset (−200-600 ms) and the steady state visual evoked potentials (SSVEP) inside the video of human walking 3D-animation in three conditions: Normal; Upside-down (inverted images); and Uncoordinated (pseudo-randomly mixed images). We found that early visual evoked response P120 was decreased in Upside-down condition. The N170 and P300b amplitudes were decreased in Uncoordinated condition. In Upside-down and Uncoordinated conditions, we found decreased alpha power and theta phase-locking. As regards gamma oscillation, power was increased during the Upside-down animation and decreased during the Uncoordinated animation. An SSVEP-like response oscillating at about 10 Hz was also described showing that the oscillating pattern is enhanced 300 ms after the heel strike event only in the Normal but not in the Upside-down condition. Our results are consistent with most of previous point-light display studies, further supporting possible use of virtual reality for neurofeedback applications.

Research paper thumbnail of Physiological modules for generating discrete and rhythmic movements: action identification by a dynamic recurrent neural network

Frontiers in Computational Neuroscience, 2014

A central question in Neuroscience is that of how the nervous system generates the spatiotemporal... more A central question in Neuroscience is that of how the nervous system generates the spatiotemporal commands needed to realize complex gestures, such as handwriting. A key postulate is that the central nervous system (CNS) builds up complex movements from a set of simpler motor primitives or control modules. In this study we examined the control modules underlying the generation of muscle activations when performing different types of movement: discrete, point-to-point movements in eight different directions and continuous figure-eight movements in both the normal, upright orientation and rotated 90 • . To test for the effects of biomechanical constraints, movements were performed in the frontal-parallel or sagittal planes, corresponding to two different nominal flexion/abduction postures of the shoulder. In all cases we measured limb kinematics and surface electromyographic activity (EMG) signals for seven different muscles acting around the shoulder. We first performed principal component analysis (PCA) of the EMG signals on a movement-by-movement basis. We found a surprisingly consistent pattern of muscle groupings across movement types and movement planes, although we could detect systematic differences between the PCs derived from movements performed in each shoulder posture and between the principal components associated with the different orientations of the figure. Unexpectedly we found no systematic differences between the figure eights and the point-to-point movements. The first three principal components could be associated with a general co-contraction of all seven muscles plus two patterns of reciprocal activation. From these results, we surmise that both "discreterhythmic movements" such as the figure eight, and discrete point-to-point movement may be constructed from three different fundamental modules, one regulating the impedance of the limb over the time span of the movement and two others operating to generate movement, one aligned with the vertical and the other aligned with the horizontal.

Research paper thumbnail of A five-state P300-based foot lifter orthosis: Proof of concept

2012 ISSNIP Biosignals and Biorobotics Conference: Biosignals and Robotics for Better and Safer Living (BRC), 2012

Current lower limb prostheses do not integrate recent developments in robotics and in Brain-Compu... more Current lower limb prostheses do not integrate recent developments in robotics and in Brain-Computer Interfaces (BCIs). In fact, active lower limb prostheses seldom consider the user's intent, they often determine the correct movement from those of healthy parts of the body or from the residual limb. Recently, an emerging idea for non-invasive BCIs was proposed to allow such low bitrate systems to control a lower limb prosthesis thanks to a Central Pattern Generator (CPG) widely used in robotics. This CPG allows to automatically generate a periodic gait pattern. Furthermore, the CPG pattern frequency and magnitude can be adapted according to the specific gait behavior of the patient and his desired speed. This paper proves the concept of combining a human gait model based on a CPG and a classic but non-natural P300 BCI in order to consider the user's intent. The details of how the entire chain can be practically implemented are given. Finally, preliminary results on four healthy subjects for a four-speed P300-based lower limb orthosis with a non-control state are presented. Globally, results are satisfying and prove the feasibility of such systems.

Research paper thumbnail of Optimizing the Performances of a P300-Based Brain–Computer Interface in Ambulatory Conditions

IEEE Journal on Emerging and Selected Topics in Circuits and Systems, 2011

Brain-computer interfaces (BCIs) enable their users to interact with their surrounding environmen... more Brain-computer interfaces (BCIs) enable their users to interact with their surrounding environment using the activity of their brain only, without activating any muscle. This technology provides severely disabled people with an alternative mean to communicate or control any electric device. On the other hand, BCI applications are more and more dedicated to healthier people, with the aim of giving them access to augmented reality or new rehabilitation tools. As it is noninvasive, light and relatively cheap, electroencephalography (EEG) is the most used acquisition technique to record cerebral activity of the BCI users. However, when using such type of BCI, user movements are likely to provoke motions of the measuring electrodes which can severely damage the EEG quality. Thus, current BCI technology requires that the user sits and performs as little movements as possible. This is of course a strong limitation of BCI for use in ordinary life. Very recently, preliminary studies have been published in the literature and suggest that BCI applications can be realized even in the physically moving context. In this paper, we thoroughly investigate the possibility to develop a P300-based BCI system in ambulatory condition. The study is based on experimental data recorded with seven subjects executing a visual P300 speller-like discrimination task while simultaneously walking at different speeds on a treadmill. It is demonstrated that a P300-based BCI is definitely feasible in such conditions. Different artifact correction methods are described and discussed in detail. To conclude, a recommended approach is given for the development of a real-time application.

Research paper thumbnail of Physiological modules for generating discrete and rhythmic movements: component analysis of EMG signals

Frontiers in Computational Neuroscience, 2015

A central question in Neuroscience is that of how the nervous system generates the spatiotemporal... more A central question in Neuroscience is that of how the nervous system generates the spatiotemporal commands needed to realize complex gestures, such as handwriting. A key postulate is that the central nervous system (CNS) builds up complex movements from a set of simpler motor primitives or control modules. In this study we examined the control modules underlying the generation of muscle activations when performing different types of movement: discrete, point-to-point movements in eight different directions and continuous figure-eight movements in both the normal, upright orientation and rotated 90 • . To test for the effects of biomechanical constraints, movements were performed in the frontal-parallel or sagittal planes, corresponding to two different nominal flexion/abduction postures of the shoulder. In all cases we measured limb kinematics and surface electromyographic activity (EMG) signals for seven different muscles acting around the shoulder. We first performed principal component analysis (PCA) of the EMG signals on a movement-by-movement basis. We found a surprisingly consistent pattern of muscle groupings across movement types and movement planes, although we could detect systematic differences between the PCs derived from movements performed in each shoulder posture and between the principal components associated with the different orientations of the figure. Unexpectedly we found no systematic differences between the figure eights and the point-to-point movements. The first three principal components could be associated with a general co-contraction of all seven muscles plus two patterns of reciprocal activation. From these results, we surmise that both "discreterhythmic movements" such as the figure eight, and discrete point-to-point movement may be constructed from three different fundamental modules, one regulating the impedance of the limb over the time span of the movement and two others operating to generate movement, one aligned with the vertical and the other aligned with the horizontal.

Research paper thumbnail of Control of Leg Movements Driven by EMG Activity of Shoulder Muscles

Frontiers in Human Neuroscience, 2014

During human walking, there exists a functional neural coupling between arms and legs, and betwee... more During human walking, there exists a functional neural coupling between arms and legs, and between cervical and lumbosacral pattern generators. Here, we present a novel approach for associating the electromyographic (EMG) activity from upper limb muscles with leg kinematics. Our methodology takes advantage of the high involvement of shoulder muscles in most locomotor-related movements and of the natural co-ordination between arms and legs. Nine healthy subjects were asked to walk at different constant and variable speeds (3-5 km/h), while EMG activity of shoulder (deltoid) muscles and the kinematics of walking were recorded. To ensure a high level of EMG activity in deltoid, the subjects performed slightly larger arm swinging than they usually do. The temporal structure of the burst-like EMG activity was used to predict the spatiotemporal kinematic pattern of the forthcoming step. A comparison of actual and predicted stride leg kinematics showed a high degree of correspondence (r > 0.9). This algorithm has been also implemented in pilot experiments for controlling avatar walking in a virtual reality setup and an exoskeleton during over-ground stepping. The proposed approach may have important implications for the design of human-machine interfaces and neuroprosthetic technologies such as those of assistive lower limb exoskeletons.

Research paper thumbnail of An analysis of EEG signals during voluntary rhythmic foot movements

2011 5th International IEEE/EMBS Conference on Neural Engineering, 2011

Human locomotion is based on complex interactions of several cortical and subcortical structures.... more Human locomotion is based on complex interactions of several cortical and subcortical structures. Over the years, the main underlying mechanisms have been partially unveiled thanks to standard functional neuroimaging techniques as well as electroencephalography (EEG). However, a complete picture is still lacking to date, due to particularly challenging experimental difficulties arising on top of the inherent complexity of the involved mechanisms. In this context, the aim of this study was to investigate the EEG dynamics associated to the production of voluntary rhythmic foot movements only. We used an experimental protocol limiting drastically the presence of movement artifacts in the EEG signals compared to real walk on a treadmill. A time-frequency analysis was performed, based on a time-warping method allowing an ensemble averaging of the data of 3 subjects. Characteristic alternation of power increases and decreases in the alpha, beta and gamma bands during the movement cycle is demonstrated as well as the emergence of two different neural coordination schemes related to in-phase and anti-phase foot movements.