Loss of brain inter-frequency hubs in Alzheimer's disease

Alzheimer's disease (AD) causes alterations of brain network structure and function. The latter consists of connectivity changes between oscillatory processes at different frequency channels. We proposed a multi-layer network approach to analyze multiple-frequency brain networks inferred from magnetoencephalographic recordings during resting-states in AD subjects and age-matched controls. Main results showed that brain networks tend to facilitate information propagation across different frequencies, as measured by the multi-participation coefficient (MPC). However, regional connectivity in AD subjects was abnormally distributed across frequency bands as compared to controls, causing significant decreases of MPC. This effect was mainly localized in association areas and in the cingulate cortex, which acted, in the healthy group, as a true inter-frequency hub. MPC values significantly correlated with memory impairment of AD subjects, as measured by the total recall score. Most predictive regions belonged to components of the default-mode network that are typically affected by atrophy, metabolism disruption and amyloid-beta deposition. We evaluated the diagnostic power of the MPC and we showed that it led to increased classification accuracy (78.39%) and sensitivity (91.11%). These findings shed new light on the brain functional alterations underlying AD and provide analytical tools for identifying multi-frequency neural mechanisms of brain diseases.Comment: 27 pages, 6 figures, 3 tables, 3 supplementary figure

Integrating EEG and MEG signals to improve motor imagery classification in brain-computer interfaces

We propose a fusion approach that combines features from simultaneously recorded electroencephalographic (EEG) and magnetoencephalographic (MEG) signals to improve classification performances in motor imagery-based brain-computer interfaces (BCIs). We applied our approach to a group of 15 healthy subjects and found a significant classification performance enhancement as compared to standard single-modality approaches in the alpha and beta bands. Taken together, our findings demonstrate the advantage of considering multimodal approaches as complementary tools for improving the impact of non-invasive BCIs

Sensory-motor interactions in speech perception, production and imitation: behavioral evidence from close shadowing, perceptuo-motor phonemic organization and imitative changes.

International audienceSpeech communication can be viewed as an interactive process involving a functional coupling between sensory and motor systems. In the present study, we combined three classical experimental paradigms to further test perceptuomotor interactions in both speech perception and production. In a first close shadowing experiment, auditory and audiovisual syllable identification led to faster oral than manual responses. In a second experiment, participants were asked to produce and to listen to French vowels, varying from height feature, in order to test perceptuo-motor phonemic organization and idiosyncrasies. In a third experiment, online imitative changes on the fundamental frequency in relation to acoustic vowel targets were observed in a non-interactive situation of communication during both unintentional and voluntary imitative production tasks. Altogether our results appear exquisitely in line with a functional coupling between action and perception speech systems and provide further evidence for a sensory-motor nature of speech representations

Sensory-motor interactions in speech perception, production and imitation: behavioral evidence from close shadowing, perceptuo-motor phonemic organization and imitative changes.

International audienceSpeech communication can be viewed as an interactive process involving a functional coupling between sensory and motor systems. In the present study, we combined three classical experimental paradigms to further test perceptuomotor interactions in both speech perception and production. In a first close shadowing experiment, auditory and audiovisual syllable identification led to faster oral than manual responses. In a second experiment, participants were asked to produce and to listen to French vowels, varying from height feature, in order to test perceptuo-motor phonemic organization and idiosyncrasies. In a third experiment, online imitative changes on the fundamental frequency in relation to acoustic vowel targets were observed in a non-interactive situation of communication during both unintentional and voluntary imitative production tasks. Altogether our results appear exquisitely in line with a functional coupling between action and perception speech systems and provide further evidence for a sensory-motor nature of speech representations

The shadow of a doubt? Evidence for perceptuo-motor linkage during auditory and audiovisual close-shadowing

One classical argument in favor of a functional role of the motor system in speech perception comes from the close shadowing task in which a subject has to identify and to repeat as quickly as possible an auditory speech stimulus. The fact that close shadowing can occur very rapidly and much faster than manual identification of the speech target is taken to suggest that perceptually-induced speech representations are already shaped in a motor-compatible format. Another argument is provided by audiovisual interactions often interpreted as referring to a multisensory-motor framework. In this study, we attempted to combine these two paradigms by testing whether the visual modality could speed motor response in a close-shadowing task. To this aim, both oral and manual responses were evaluated during the perception of auditory and audio-visual speech stimuli, clear or embedded in white noise. Overall, oral responses were faster than manual ones, but it also appeared that they were less accurate in noise, which suggests that motor representations evoked by the speech input could be rough at a first processing stage. In the presence of acoustic noise, the audiovisual modality led to both faster and more accurate responses than the auditory modality. No interaction was however observed between modality and response. Altogether, these results are interpreted within a two-stage sensory-motor framework, in which the auditory and visual streams are integrated together and with internally generated motor representations before a final decision may be available

L'ombre d'un doute ? Interactions perceptivo-motrices lors de tâches de close-shadowing auditive et audio-visuelles

International audienceOne classical argument in favor of a functional role of the motor system in speech perception comes from the close shadowing task in which a subject has to identify and to repeat as quickly as possible an auditory speech stimulus. The fact that close shadowing can occur very rapidly and much faster than manual identification of the speech target is taken to suggest that perceptually-induced speech representations are already shaped in a motor-compatible format. Another argument is provided by audiovisual interactions often interpreted as referring to a multisensory-motor framework. In this study, we attempted to combine these two paradigms by testing whether the visual modality could speed motor response in a close-shadowing task. To this aim, both oral and manual responses were evaluated during the perception of auditory and audio-visual speech stimuli, clear or embedded in white noise. Overall, oral responses were much faster than manual ones, but it also appeared that they were less accurate in noise, which suggests that motor representations evoked by the speech input could be rough at a first processing stage. In the presence of acoustic noise, the audiovisual modality led to both faster and more accurate responses than the auditory modality. No interaction was however observed between modality and response. Altogether, these results are interpreted within a two-stage sensory-motor framework, in which the auditory and visual streams are integrated together and with internally generated motor representations before a final decision may be available.Un argument classique en faveur des théories motrices de la perception de la parole provient du paradigme de " close-shadowing " (répétition rapide). Le fait que cette tâche de close-shadowing entraîne des réponses orales bien plus rapides qu'en réponses manuelles suggère en effet un codage des représentations perceptives dans un format moteur, compatible avec une réponse orale. Un autre argument est apporté par les interactions audio-visuelles lors de la perception de parole, souvent interprétées en référence à un couplage fonctionnel entre audition, vision et motricité. Dans cette étude, nous avons combiné ces deux paradigmes de manière à tester si la modalité visuelle pouvait induire des réponses motrices plus rapides lors d'une tâche de close-shadowing. Pour ce faire, différentes tâches de catégorisation orale et manuelle de stimuli de parole présentés auditivement ou audio-visuellement, en présence ou non d'un bruit blanc, ont été réalisées. De manière générale, les réponses orales ont été plus rapides que les réponses manuelles, mais aussi moins précises, notamment dans le bruit, ce qui suggère que la représentation motrice induite par la stimulation pourrait être peu précise dans un premier niveau de traitement. En présence d'un bruit acoustique, la modalité audiovisuelle s'est avérée à la fois plus rapide et plus précise que la modalité auditive. Aucune interaction entre le mode de réponse et la modalité de présentation des stimuli n'a cependant été observée. Nous interprétons l'ensemble de ces résultats dans un cadre théorique proposant l'existence de boucles perceptivo-motrices, dans lesquelles les entrées auditives et visuelles seraient intégrées et reliées à la génération interne de représentations motrices préalablement au processus final de décision

Permafrost extension modeling in rock slope since the Last Glacial Maximum: application to the large Séchilienne landslide (French Alps).

12 pagesInternational audienceRecent dating performed on large landslides in the Alps reveal that the initiation of instability did not immediately follow deglaciation but occurred several thousand years after ice down-wastage in the valleys. This result indicates that debuttressing is not the immediate cause of landslide initiation. The period of slope destabilization appears to coincide with the wetter and warmer Holocene Climatic Optimum, indicating a climatic cause of landslide triggering, although the role of seismic activity cannot be ruled out. A phenomenon which may partly explain the delay between valley deglaciation and gravitational instability is the temporal persistence of thick permafrost layers developed in the Alps since the Last Glacial Maximum (LGM). This hypothesis was tested through 2D thermal numerical modeling of the large Séchilienne landslide (Romanche valley, French Alps) using plausible input parameter values. Simulation results suggest that permafrost vanished in the Séchilienne slope at 10 to 11 ka, 3,000 to 4,000 years following the total ice down-wastage of the Romanche valley at 14.3 ka. Permafrost persistence could have contributed to the failure delay by temporally strengthening the slope. Numerical simulations also show that the permafrost depth expansion approximately fits the thickness of ground affected by gravitational destabilization, as deduced from geophysical investigations. These results further suggest that permafrost development, associated with an ice segregation mechanism, damaged the rock slope and influenced the resulting landslide geometry

L'ombre d'un doute ? Interactions perceptivo-motrices lors de tâches de close-shadowing auditive et audio-visuelles

International audienceOne classical argument in favor of a functional role of the motor system in speech perception comes from the close shadowing task in which a subject has to identify and to repeat as quickly as possible an auditory speech stimulus. The fact that close shadowing can occur very rapidly and much faster than manual identification of the speech target is taken to suggest that perceptually-induced speech representations are already shaped in a motor-compatible format. Another argument is provided by audiovisual interactions often interpreted as referring to a multisensory-motor framework. In this study, we attempted to combine these two paradigms by testing whether the visual modality could speed motor response in a close-shadowing task. To this aim, both oral and manual responses were evaluated during the perception of auditory and audio-visual speech stimuli, clear or embedded in white noise. Overall, oral responses were much faster than manual ones, but it also appeared that they were less accurate in noise, which suggests that motor representations evoked by the speech input could be rough at a first processing stage. In the presence of acoustic noise, the audiovisual modality led to both faster and more accurate responses than the auditory modality. No interaction was however observed between modality and response. Altogether, these results are interpreted within a two-stage sensory-motor framework, in which the auditory and visual streams are integrated together and with internally generated motor representations before a final decision may be available.Un argument classique en faveur des théories motrices de la perception de la parole provient du paradigme de " close-shadowing " (répétition rapide). Le fait que cette tâche de close-shadowing entraîne des réponses orales bien plus rapides qu'en réponses manuelles suggère en effet un codage des représentations perceptives dans un format moteur, compatible avec une réponse orale. Un autre argument est apporté par les interactions audio-visuelles lors de la perception de parole, souvent interprétées en référence à un couplage fonctionnel entre audition, vision et motricité. Dans cette étude, nous avons combiné ces deux paradigmes de manière à tester si la modalité visuelle pouvait induire des réponses motrices plus rapides lors d'une tâche de close-shadowing. Pour ce faire, différentes tâches de catégorisation orale et manuelle de stimuli de parole présentés auditivement ou audio-visuellement, en présence ou non d'un bruit blanc, ont été réalisées. De manière générale, les réponses orales ont été plus rapides que les réponses manuelles, mais aussi moins précises, notamment dans le bruit, ce qui suggère que la représentation motrice induite par la stimulation pourrait être peu précise dans un premier niveau de traitement. En présence d'un bruit acoustique, la modalité audiovisuelle s'est avérée à la fois plus rapide et plus précise que la modalité auditive. Aucune interaction entre le mode de réponse et la modalité de présentation des stimuli n'a cependant été observée. Nous interprétons l'ensemble de ces résultats dans un cadre théorique proposant l'existence de boucles perceptivo-motrices, dans lesquelles les entrées auditives et visuelles seraient intégrées et reliées à la génération interne de représentations motrices préalablement au processus final de décision

The influence of bedrock topography on the dynamics of two clayey landslides in the Trièves (French Alps)

International audienceThe two large adjacent landslides of Avignonet and Harmalière, affecting thick clayey quater- nary deposits, are located in the Trièves area (French Alps). Remote techniques (Lidar) and GPS measure- ments were used to characterize the two landslides. Results show major differences between the dynamics of the two landslides, both in morphology, displacement rate magnitudes and motion directions. Seismic noise measurements (H/V technique) were performed to map the clay layer thickness. Combined with Lidar derived DEM, these data yielded the paleo-topography of the seismic substratum made of compact alluvial layers and Mesozoic bedrock. The difference in dynamics between the two landslides is likely to result from the pres- ence of a ridge of compact formations at the Avignonet landslide toe, preventing an eastward deep active slid- ing to develop and explaining the observed shallow slip surfaces. To the South, this buttress disappears at the Harmalière toe, favoring a deep sliding in a Southeastern direction with a fast regression of the headscarp, which evolves into a mudslide at its base