Alterations of EEG rhythms during motor preparation following awake brain surgery

International audienceSlow-growing, infiltrative brain tumours may modify the electrophysiological balance between the two hemispheres. To determine whether and how asymmetry of EEG rhythms during motor preparation might occur following " awake brain surgery " for this type of tumour, we recorded electroencephalograms during a simple visuo-manual reaction time paradigm performed by the patients between 3 and 12 months after surgery and compared them to a control group of 8 healthy subjects. Frequency analyses revealed imbalances between the injured and healthy hemispheres. More particularly, we observed a power increase in the δ frequency band near the lesion site and a power increase in the α and β frequency bands. Interestingly, these alterations seem to decrease for the two patients whose surgery were anterior to 9 months, independently of the size of the lesion. Reaction times did not reflect this pattern as they were clearly not inversely related to the anteriority of the surgery. Electrophysiology suggests here different processes of recovery compared to behavioral data and brings further insights for the understanding of EEG rhythms that should not be systematically confounded or assimilated with cognitive performances. EEG monitoring is rare for these patients, especially after awake brain surgery, however it is important

Statistical behavior of edge detectors

National audienceno abstrac

Statistical behavior of edge detectors

National audienceno abstrac

Dynamique des fluctuations posturales et influence de l'avancé en âge

L étude de l équilibre orthostatique a fait l objet de nombreuses études s attachant à l analyse des déplacements du centre des pressions comme indicateur de l efficience du contrôle postural. Plus particulièrement, une large littérature se concentre sur l étude des mesures stabilométriques notamment en lien avec l avancée en âge. En effet, le vieillissement s accompagne généralement d une altération du système postural pouvant avoir diverses conséquences telles que l occurrence de chutes. Jusqu à présent, la caractérisation des effets de l âge sur la stabilité posturale à partir des mesures stabilométriques reste limitée par la nature même des paramètres utilisés. Dans ce travail, nous proposons l utilisation de nouvelles méthodes issues de la théorie des systèmes dynamiques pour définir des signatures posturales propres à l avancée en âge. Ces méthodes s appuient sur l analyse de la structure temporelle des fluctuations posturales et peuvent fournir une information sur leur degré de complexité. Pour ce faire, cinq études ont été réalisées. L étude 1 a montré que le vieillissement affecte de manière significative la dynamique des déplacements du centre des pressions. Plus précisément, une personne âgée oscille de manière plus importante et avec une structure temporelle des oscillations posturales différentes d un sujet jeune. Les études 2 et 3, à caractère méthodologique, renforcent l hypothèse d un caractère stochastique, et donc non chaotique, de la dynamique des déplacements du centre des pressions. Ces deux études ont également permis de développer et de tester deux paramètres dynamiques apportant chacun une information différente sur la structure des fluctuations posturales. L étude 4 a montré que les mesures dynamiques et stabilométriques sont complémentaires et que certaines ont une sensibilité à l âge. Elle suggère également que les différentsparamètres dynamiques ne sont pas forcément redondants. L étude 5 explore l effet d un entrainement de trois mois, sollicitant notamment les capacités d équilibration, sur la structure dynamique des oscillations posturales de la personne âgée.The study of postural balance has been the subject of numerous studies focusing on the analysis of the pressure center displacement as an indicator of postural control efficiency. Specifically, a large literature focuses on the study of stabilometric measures particularly in relation with age advancing. Indeed, aging coincides with the deterioration of the postural system and its functional consequences, one of which is the fall. Until now, the characterization of the effects of age on postural stability of stabilometric measures has remained limited by the nature of the parameters used. In this work, we propose the use of new methods from dynamical system theories to define postural signatures in relation with aging. These methods are based on the analysis of the temporal structure of postural fluctuations and can provide information on their degree of complexity. Five studies have been conducted. Study 1 showed that aging significantly affects the dynamics of displacements of the pressure center. More precisely, a senior s measures show a significant difference in the temporal structure compared to a young subject. Studies 2 and 3, more particularly focused on methodology, reinforcing the hypothesis of a stochastic nature of the dynamics (and therefore not chaotic) of postural oscilations. These two studies also allowed to develop and test two dynamical parameters, each providing different information on the structure of postural fluctuations. Study 4 showed that the dynamical and stabilometric measures are complementary and are influenced by age. This study has underlined the non-redundancy of information from each dynamical parameter. Study 5 explored the effect of a three-months training, including specific balance exercises, on the dynamical structure of postural sway of the elderlyMONTPELLIER-BU STAPS (341722109) / SudocSudocFranceF

Detecting high-dimensional determinism in time series with application to human movement data.

International audienceno abstrac

Probabilistic analysis of recurrence plots generated by fractional Gaussian noise

International audienceRecurrence plots of time series generated by discrete fractional Gaussian noise (fGn) processes are analyzed. We compute the probabilities of occurrence of consecutive recurrence points forming diagonals and verticals in the recurrence plot constructed without embedding. We focus on two recurrence quantification analysis measures related to these lines, respectively, the percent determinism and the laminarity (LAM). The behavior of these two measures as a function of the fGn’s Hurst exponent $H$ is investigated. We show that the dependence of the laminarity with respect to $H$ is monotonic in contrast to the percent determinism. We also show that the length of the diagonal and vertical lines involved in the computation of percent determinism and laminarity has an influence on their dependence on $H$. Statistical tests performed on the $LAM$ measure support its utility to discriminate fGn processes with respect to their $H$ values. These results demonstrate that recurrence plots are suitable for the extraction of quantitative information on the correlation structure of these widespread stochastic processes

Detecting high-dimensional determinism in time series with application to human movement data.

International audienceno abstrac

Dynamical structure of center of pressure fluctuations in elderly people

International audienceThis article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyrigh

Modeling Postural Coordination Dynamics using a Closed-Loop Controller

International audienceThis paper models recent data in the field of postural coordination showing the existence of self-organized postural states, and transition between them, underlying supra-postural tracking movements. The proposed closed-loop controller captures the complex postural behaviors observed in humans and can be used to implement efficient and simple balance control principles in humanoids