E. Houdayer

Perceiving What Is Reachable Depends on Motor Representations: Evidence from a Transcranial Magnetic Stimulation Study

Background Visually determining what is reachable in peripersonal space requires information about the egocentric location of objects but also information about the possibilities of action with the body, which are context dependent. The aim of the present study was to test the role of motor representations in the visual perception of peripersonal space. Methodology Seven healthy participants underwent a TMS study while performing a right-left decision (control) task or perceptually judging whether a visual target was reachable or not with their right hand. An actual grasping movement task was also included. Single pulse TMS was delivered 80% of the trials on the left motor and premotor cortex and on a control site (the temporo-occipital area), at 90% of the resting motor threshold and at different SOA conditions (50ms, 100ms, 200ms or 300ms). Principal Findings Results showed a facilitation effect of the TMS on reaction times in all tasks, whatever the site stimulated and until 200ms after stimulus presentation. However, the facilitation effect was on average 34ms lower when stimulating the motor cortex in the perceptual judgement task, especially for stimuli located at the boundary of peripersonal space. Conclusion This study provides the first evidence that brain motor area participate in the visual determination of what is reachable. We discuss how motor representations may feed the perceptual system with information about possible interactions with nearby objects and thus may contribute to the perception of the boundary of peripersonal space.

Post-movement beta synchronization in subjects presenting with sensory deafferentation

OBJECTIVEnWe studied the time course and location of post-movement beta synchronization (PMBS) in patients presenting with sensory deafferentation, in order to assess the hypothetical relationship between the PMBS and the cortical processing of movement-related somatosensory afferent inputs.nnnMETHODSnWe used the event-related synchronization (ERS) method. EEG activity was recorded (via a 128-electrode system) during brisk, unilateral right and left index finger extension by 10 patients presenting with neuropathic pain related to sensory deafferentation. Intra- and post-movement changes in beta source power were calculated relative to pre-movement baseline activity. We compared the PMBS results for the painful and non-painful body sides. Furthermore, PMBS patterns in patients were compared with those in nine healthy volunteers.nnnRESULTSnPMBS pattern related to the painful side had a spatial distribution, with an ipsilateral preponderance, significantly more restricted than PMBS pattern on the non-painful side and in the control group. There were no significant differences between patient PMBS patterns on the non-painful side and those in the control group.nnnCONCLUSIONSnSensory deafferentation disrupts normal PMBS patterns.nnnSIGNIFICANCEnThis work provides additional arguments to the hypothesis supporting that the PMBS is influenced by movement-related somatosensory input processing.

Attention impairment in temporal lobe epilepsy: A neurophysiological approach via analysis of the P300 wave

Purpose: Attention is often impaired in temporal lobe epilepsy (TLE). The P300 wave (an endogenous, event‐related potential) is a correlate of attention which is usually recorded during an “oddball paradigm,” where the subject is instructed to detect an infrequent target stimulus presented amongst frequent, standard stimuli. Modifications of the P300 waves latency and amplitude in TLE have been suggested, but it is still not known whether the source regions also differ. Our hypothesis was that temporal lobe dysfunction would modify the P3 source regions in TLE patients. Methods: A comparative, high density, 128‐channel electroencephalographic analysis of the characteristics of P300 (P3b latency and amplitude) was performed in 10 TLE patients and 10 healthy controls during auditory and visual oddball paradigms. The P3b sources were localized on individual 3D MR images using the LORETA method and intergroup statistical comparisons were performed using SPM2® software. Results: Our main results (in both individual analyses and intergroup comparisons) revealed a reduction in temporal (and more particularly mesiotemporal) sources and, to a lesser extent, frontal sources in TLE patients, compared with controls. Discussion: This reduction may reflect direct, local cortical dysfunction caused by the epileptic focus or more complex interference between epileptic networks and normal attentional pathways. Hum Brain Mapp, 2009.

Deficient sensory beta synchronization in Parkinson's disease

OBJECTIVEnBeta rhythm movement-related synchronization (beta synchronization) reflects motor cortex deactivation and sensory afference processing. In Parkinsons disease (PD), decreased beta synchronization after active movement reflects abnormal motor cortex idling and may be involved in the pathophysiology of akinesia. The objectives of the present study were to (i) compare event-related synchronization after active and passive movement and electrical nerve stimulation in PD patients and healthy, age-matched volunteers and (ii) evaluate the effect of levodopa.nnnMETHODSnUsing a 128-electrode EEG system, we studied beta synchronization after active and passive index finger movement and electrical median nerve stimulation in 13 patients and 12 control subjects. Patients were recorded before and after 150% of their usual morning dose of levodopa.nnnRESULTSnThe peak beta synchronization magnitude in the contralateral primary sensorimotor (PSM) cortex was significantly lower in PD patients after active movement, passive movement and electrical median nerve stimulation, compared with controls. Levodopa partially reversed the drop in beta synchronization after active movement but not after passive movement or electrical median nerve stimulation.nnnDISCUSSIONnIf one considers that beta synchronization reflects sensory processing, our results suggest that integration of somaesthetic afferences in the PSM cortex is abnormal in PD during active and passive movement execution and after simple electrical median nerve stimulation.nnnSIGNIFICANCEnBetter understanding of the mechanisms involved in the deficient beta synchronization observed here could prompt the development of new therapeutic approaches aimed at strengthening defective processes. The lack of full beta synchronization restoration by levodopa might be related to the involvement of non-dopaminergic pathways.

Motor cortex stimulation modulates defective central beta rhythms in patients with neuropathic pain

OBJECTIVEnMotor cortex stimulation therapy (MCS) is increasingly used to control refractory neuropathic pain. Post-movement beta synchronization (PMBS) is defined as a sharp increase in beta-frequency electroencephalographic power following movement offset and may reflect sensorimotor cortex inhibition induced, at least in part, by cortical processing of movement-related sensory afferent inputs. PMBS pattern is then often altered in case of neuropathic pain. The main objective of the present study was to test the hypothesis that implanted MCS modulates PMBS in patients presenting with neuropathic pain.nnnMETHODSnUsing a high-resolution, 128-electrode electroencephalographic system, we recorded and compared, before and during MCS, PMBS patterns during brisk, unilateral right and left index finger extension in 8 patients presenting with neuropathic pain.nnnRESULTSnThe pre-operative PMBS patterns were altered in all cases. MCS increased the spatial distribution and amplitude of PMBS in most of cases and restored maximum-intensity of PMBS contralateral to the painful body side. These modifications appeared significantly correlated with the analgesic effect of MCS.nnnCONCLUSIONnThis study provides evidence of central beta rhythms neuromodulation induced by MCS.nnnSIGNIFICANCEnThe restoration by MCS of defective cortical inhibition in patients with neuropathic pain is evoked.

A - 21 Étude des troubles attentionnels dans l’épilepsie temporale par analyse de l’onde P300

Introduction L’epilepsie temporale (ET) s’accompagne de troubles attentionnels qu’il est possible d’explorer en electrophysiologie par l’onde P300. La localisation des generateurs de la P300 reste mal connue. Objectifs Comparer les sources de la P300 entre patients ET et sujets sains et determiner s’il existe une relation entre la lateralisation du foyer epileptique et les generateurs de l’onde. Methodes 10 patients ET et 10 sujets sains beneficierent d’un enregistrement EEG haute resolution (128 voies). Les caracteristiques de la P300 (latence, amplitude) furent mesurees au cours d’un paradigme oddball auditif et visuel. Les generateurs furent localises sur des IRM individuelles par la methode LORETA. Resultats Nous avons retrouve une augmentation de la latence et une diminution d’amplitude de la P300 dans l’ET. Par rapport aux sujets sains, les sources temporo-mesiales etaient plus rares chez les patients ET, au profit des sources temporales externes. Cette reduction apparaissait plus nette du cote du foyer epileptique. Discussion La reduction des generateurs temporo-mesiaux dans l’ET pourrait refleter une dysfonction corticale locale, secondaire a l’epilepsie et une reorganisation fonctionnelle des structures impliquees dans l’attention comme cela a deja ete montre dans la memoire episodique. La lateralisation de ces modifications est en faveur d’une implication directe du foyer epileptique sur la reduction des sources et sur les troubles attentionnels. Conclusion Le dysfonctionnement temporo-mesial pourrait etre en partie responsable des troubles attentionnels dans l’epilepsie temporale, malgre une reorganisation des reseaux attentionnels chez ces patients.

FC37.4 Modulation of sensorimotor integration in patients with writer’s cramp by subthreshold low-frequency rTMS over the premotor cortex

internus (GPi; Silberstein et al. Brain 2003;126:2597–608), but none has been reported about movement-related pallidal activity. Objective: We tested the hypothesis that there are distinct temporal patterns of synchronized movement-related neuronal activity in the GPi that characterize dystonic and normal movement. Patients and methods: Four patients (one DYT1, one hemiand two segmental dystonia) participated with informed consent. Subjects performed self-paced movement at 8–10 s interval. Tasks with dystonic movement (finger extension or vocalization) or with normal movement (finger extension or head rotation) were ordered. LFPs of the GPi were recorded from the contralateral DBS electrodes. Data were analyzed with band pass filter of 4–8 Hz. To evaluate the start and end of the desynchronized activity, cumulative sum charts and bootstrap were used. Results: ERD started earlier in normal movement (250– 450 ms before movement onset) than in dystonia (250 ms before to 50 ms after). ERD ended larger in dystonia (3050–5500 ms) than in normal movement (50–1850 ms). ERD duration was correlated with the duration of EMG activity (r = 0.8, p = 0.005). Conclusion: First, abnormal temporal desynchronized pattern of premovement in GPi may be related with the generation of dystonia. Second, EMG activity correlates with the duration of desynchronized neuronal activity in GPi.

P36.30 Modification of event related beta synchronization induced by motor cortex electrical stimulation for control of neuropathic pain

Background: The concept of ‘‘super-synergy in brain’s electrical activity’’ is described as the ensemble of five processes that act in synergy. The hypothesis is based on results of human and animal experiments from Aplysia to the cat brain (Basar 1999 Brain Oscillations II, Springer Publishers, New-York). Results and conceptual framework: According to our large database the electrical manifestations of diverse brain functions are shaped by: 1. The superposition of oscillations in the alpha, beta, gamma, theta, and delta bands. 2. Activation of more than one selectively distributed oscillations in gamma, alpha, theta and delta bands upon exogenous or endogenous input. These activities are manifested with parameters such as enhancement, delay, desynchronization, and prolongation. 3. Temporal and spatial changes of entropy in the brain. 4. Temporal coherence between cells in cortical columns for simple binding. 5. Varying degrees of spatial coherence occurring over long-distances as parallel processing. The superposition describes temporal integration; selectively distributed and selectively coherent oscillations describe spatial integration. Evaluation of combinations of these variables leads to an enormous amount of neuroelectric configurations. Spatio-temporal and functional organization of multiple and distributed oscillations in the brain inevitably leads to superbinding defined as’’ the combination of mechanisms of superposition, activation of selectively distributed oscillatory systems and large-scale coherence’’. We also comparatively analyzed the coherence function and entropy changes of alpha activity in the Aplysia ganglia, fish brain, and mammalians. The coherence in brain tissues of several species increases during evolution; the entropy is diminishing by reaching highest order in alpha activity of the human brain. Conclusion: We conclude that the alpha coherence function and entropy are key manifestation in the processes of the evolution of species.