Global Perturbation of Initial Geometry in a Biomechanical Model of Cortical Morphogenesis

Cortical folding pattern is a main characteristic of the geometry of the human brain which is formed by gyri (ridges) and sulci (grooves). Several biological hypotheses have suggested different mechanisms that attempt to explain the development of cortical folding and its abnormal evolutions. Based on these hypotheses, biomechanical models of cortical folding have been proposed. In this work, we compare biomechanical simulations for several initial conditions by using an adaptive spherical parameterization approach. Our approach allows us to study and explore one of the most potential sources of reproducible cortical folding pattern: the specification of initial geometry of the brain.Comment: 4 pages 2 columns (IEEE style), 41st EMB Conferenc

Modélisation de la relation entre le signal EMG de surface et la force musculaire par analyse de données d’un réseau de capteurs à haute résolution

The neuromuscular and musculoskeletal systems are complex System of Systems (SoS) that perfectly interact to provide motion. This interaction is illustrated by the muscular force, generated by muscle activation driven by the Central Nervous System (CNS) which pilots joint motion. The knowledge of the force level is highly important in biomechanical and clinical applications. However, the recording of the force produced by a unique muscle is impossible using noninvasive procedures. Therefore, it is necessary to develop a way to estimate it. The muscle activation also generates another electric phenomenon, measured at the skin using electrodes, namely the surface electromyogram (sEMG). ln the biomechanics literature, several models of the sEMG/force relationship are provided. They are principally used to command musculoskeletal models. However, these models suffer from several important limitations such lacks of physiological realism, personalization, and representability when using single sEMG channel input. ln this work, we propose to construct a model of the sEMG/force relationship for the Biceps Brachii (BB) based on the data analysis of a High Density sEMG (HD-sEMG) sensor network. For this purpose, we first have to prepare the data for the processing stage by denoising the sEMG signals and removing the parasite signals. Therefore, we propose a HD-sEMG denoising procedure based on Canonical Correlation Analysis (CCA) that removes two types of noise that degrade the sEMG signals and a source separation method that combines CCA and image segmentation in order to separate the electrical activities of the BB and the Brachialis (BR). Second, we have to extract the information from an 8 X 8 HD-sEMG electrode grid in order to form the input of the sEMG/force model Thusly, we investigated different parameters that describe muscle activation and can affect the relationship shape then we applied data fusion through an image segmentation algorithm. Finally, we proposed a new HDsEMG/force relationship, using simulated data from a realistic HD-sEMG generation model of the BB and a Twitch based model to estimate a specific force profile corresponding to a specific sEMG sensor network and muscle configuration. Then, we tested this new relationship in force estimation using both machine learning and analytical approaches. This study is motivated by the impossibility of obtaining the intrinsic force from one muscle in experimentation.Les systèmes neuromusculaires et musculo-squelettique sont considérés comme un système de systèmes complexe. En effet, le mouvement du corps humain est contrôlé par le système nerveux central par l'activation des cellules musculaires squelettiques. L'activation du muscle produit deux phénomènes différents : mécanique et électrique. Ces deux activités possèdent des propriétés différentes, mais l'activité mécanique ne peut avoir lieu sans l'activité électrique et réciproquement. L'activité mécanique de la contraction du muscle squelettique est responsable du mouvement. Le mouvement étant primordial pour la vie humaine, il est crucial de comprendre son fonctionnement et sa génération qui pourront aider à détecter des déficiences dans les systèmes neuromusculaire et musculo-squelettique. Ce mouvement est décrit par les forces musculaires et les moments agissant sur une articulation particulière. En conséquence, les systèmes neuromusculaires et musculo-squelettique peuvent être évalués avec le diagnostic et le management des maladies neurologiques et orthopédiques à travers l'estimation de la force. Néanmoins, la force produite par un seul muscle ne peut être mesurée que par une technique très invasive. C'est pour cela, que l'estimation de cette force reste l'un des grands challenges de la biomécanique. De plus, comme dit précédemment, l'activation musculaire possède aussi une réponse électrique qui est corrélée à la réponse mécanique. Cette résultante électrique est appelée l'électromyogramme (EMG) et peut être mesurée d'une façon non invasive à l'aide d'électrodes de surface. L'EMG est la somme des trains de potentiel d'action d'unité motrice qui sont responsable de la contraction musculaire et de la génération du mouvement. Ce signal électrique peut être mesuré par des électrodes à la surface de la peau et est appelé I'EMG de surface {sEMG). Pour un muscle unique, en supposant que la relation entre l'amplitude du sEMG et la force est monotone, plusieurs études ont essayé d'estimer cette force en développant des modèles actionnés par ce signal. Toutefois, ces modèles contiennent plusieurs limites à cause des hypothèses irréalistes par rapport à l'activation neurale. Dans cette thèse, nous proposons un nouveau modèle de relation sEMG/force en intégrant ce qu'on appelle le sEMG haute définition (HD-sEMG), qui est une nouvelle technique d'enregistrement des signaux sEMG ayant démontré une meilleure estimation de la force en surmontant le problème de la position de l'électrode sur le muscle. Ce modèle de relation sEMG/force sera développé dans un contexte sans fatigue pour des contractions isométriques, isotoniques et anisotoniques du Biceps Brachii (BB) lors une flexion isométrique de l'articulation du coude à 90°

Long term evolution of fast ripples during epileptogenesis

International audienceObjective.Fast ripples (FRs) have received considerable attention in the last decade since they represent an electrophysiological biomarker of the epileptogenic zone (EZ). However, the real dynamics underlying the occurrence, amplitude, and time-frequency content of FRs generation during epileptogenesis are still not well understood. This work aims at characterizing and explaining the evolution of these features.Approach.Intracortical electroencephalographic signals recorded in a kainate mouse model of temporal lobe epilepsy were processed in order to compute specific FR features. Then realistic physiologically based computational modeling was employed to explore the different elements that can explain the mechanisms of epileptogenesis and simulate the recorded FR in the early and late latent period.Main results.Results indicated that continuous changes of FR features are mainly portrayed by the epileptic (pathological) tissue size and synaptic properties. Furthermore, the microelectrodes characteristics were found to dramatically affect the observability and spectral/temporal content of FRs. Consequently, FRs evolution seems to mirror the continuous pathophysiological mechanism changes that occur during epileptogenesis as long as the microelectrode properties are taken into account.Significance.Our study suggests that FRs can account for the pathophysiological changes which might explain the EZ generation and evolution and can contribute in the treatment plan of pharmaco-resistant epilepsies

Robust Functional Statistics applied to Probability Density Function Shape screening of sEMG data

International audienceRecent studies pointed out possible shapemodifications of the Probability Density Function (PDF) ofsurface electromyographical (sEMG) data according to severalcontexts like fatigue and muscle force increase. Following thisidea, criteria have been proposed to monitor these shapemodifications mainly using High Order Statistics (HOS)parameters like skewness and kurtosis. In experimentalconditions, these parameters are confronted with small samplesize in the estimation process. This small sample size induceserrors in the estimated HOS parameters restraining real-timeand precise sEMG PDF shape monitoring. Recently, afunctional formalism, the Core Shape Model (CSM), has beenused to analyse shape modifications of PDF curves. In thiswork, taking inspiration from CSM method, robust functionalstatistics are proposed to emulate both skewness and kurtosisbehaviors. These functional statistics combine both kerneldensity estimation and PDF shape distances to evaluate shapemodifications even in presence of small sample size. Then, theproposed statistics are tested, using Monte Carlo simulations,on both normal and Log-normal PDFs that mimic observedsEMG PDF shape behavior during muscle contraction.According to the obtained results, the functional statistics seemto be more robust than HOS parameters to small sample sizeeffect and more accurate in sEMG PDF shape screeningapplications

Analysis of the sEMG/force relationship using HD-sEMG technique and data fusion: A simulation study

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On early brain folding patterns using biomechanical growth modeling

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Carbon and metal microelectrodes for recording of epileptic High Frequency Oscillations: A comparative study

International audienceHigh Frequency Oscillations (HFO: 80-600 Hz) and particularly Fast-Ripples (FRs: 200-600 Hz) gained increasing interest over the last decade as a biomarker of epileptogenic networks. FRs were shown to be generated by small clusters of weakly synchronized hyperexcitable neurons, the recording of which requires the use of intracerebral microelectrodes. Nonetheless, the detection of FRs recorded using classical metal microelectrodes is very challenging. This is due to their small size which increases the impedance resulting in poor signal-to-noise ratio (SNR) and distortion. Coating electrodes with Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is a promising approach that was found to reduce their impedance by several orders of magnitude. However, it is also associated with poor adhesion to metals, which severely impacts its stability for chronic usage. In this study, we compared the performances of novel carbon microelectrodes combined with PEDOT:PSS and gold electrodes with PEDOT:PSS coating to Stainless Steel electrodes for the recording and detection of in vivo FRs (mouse hippocampus, kainate model of epilepsy). Results suggest that carbon electrodes allow for better detectability of epileptiform events and, in particular FRs. Perspectives of this work include the design of clinical hybrid (micro-macro) electrodes for the pre-surgical evaluation of patients with Drug-Resistant Epilepsy (DRE) and the design of neural implants for other applications in which chronic recording over long periods of time is required. © 2023 IEEE

Global Perturbation of Initial Geometry in a Biomechanical Model of Cortical Morphogenesis

International audienceCortical folding pattern is a main characteristic of the geometry of the human brain which is formed by gyri (ridges) and sulci (grooves). Several biological hypotheses have suggested different mechanisms that attempt to explain the development of cortical folding and its abnormal evolutions. Based on these hypotheses, biomechanical models of cortical folding have been proposed. In this work, we compare biomechanical simulations for several initial conditions by using an adaptive spherical parameterization approach. Our approach allows us to study and explore one of the most potential sources of reproducible cortical folding pattern: the specification of initial geometry of the brain

The influence of biophysical parameters in a biomechanical model of cortical folding patterns

International audienceAbnormal cortical folding patterns, such as lissencephaly, pachygyria and polymicrogyria malformations, may be related to neurodevelopmental disorders. In this context, computational modeling is a powerful tool to provide a better understanding of the early brain folding process. Recent studies based on biomechanical modeling have shown that mechanical forces play a crucial role in the formation of cortical convolutions. However, the effect of biophysical parameters in these models remain unclear. In this paper, we investigate the effect of the cortical growth, the initial geometry and the initial cortical thickness on folding patterns. In addition, we not only use several descriptors of the folds such as the dimensionless mean curvature, the surface-based three-dimensional gyrification index and the sulcal depth, but also propose a new metric to quantify the folds orientation. The results demonstrate that the cortical growth mode does almost not affect the complexity degree of surface morphology; the variation in the initial geometry changes the folds orientation and depth, and in particular, the slenderer the shape is, the more folds along its longest axis could be seen and the deeper the sulci become. Moreover, the thinner the initial cortical thickness is, the higher the spatial frequency of the folds is, but the shallower the sulci become, which is in agreement with the previously reported effects of cortical thickness

N°73 – Multiscale neuro-inspired models for interpretation of EEG signals in epilepsy patients

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