Multi-approach comparative study of EEG patterns associated with the most common forms of dementia.

Electroencephalography's (EEG) sensitivity in discriminating dementia syndromes remains unclear. This study aimed to investigate EEG markers in patients with major cognitive disorders. The studied population included 4 groups of patients: Alzheimer's disease with associated vascular lesions, Alzheimer's disease without vascular lesions (AD-V), Lewy body disease and vascular dementia (VaD); and completed by a control group composed by cognitively unimpaired patients. EEGs were analysed quantitatively using spectral analysis, functional connectivity and micro-states. By comparison to the controls, expected slowing and alterations of functional connectivity were detected in patients with dementia. Among these patients, an overall increase in power in the alpha band was observed in the VaD group, mainly when compared to the 2 AD groups, while the Alzheimer's disease without vascular lesions group exhibited increased power in the beta-2 band and higher functional connectivity in the same frequency band. Micro-state analyses revealed differences in temporal dynamics for the VaD group. A number of EEG modifications reported as markers of some syndromes were found, but others were not reproduced.

Quantitative approach to early neonatal EEG visual analysis in hypoxic-ischemic encephalopathy severity: Bridging the gap between eyes and machine.

OBJECTIVES: To identify relevant quantitative parameters for early classification of neonatal hypoxic-ischemic encephalopathy (HIE) severity from conventional EEGs. METHODS: Ninety EEGs, recorded in full-term infants within 6 h of life after perinatal hypoxia, were visually classified according to the French EEG classification into three groups of increasing HIE severity. Physiologically significant EEG features (signal amplitude, continuity and frequency content) were automatically quantified using different parameters. The EEG parameters selection was based on their ability to reproduce the visual EEG classification. Post hoc analysis based on clinical outcome was performed. RESULTS: Six EEG parameters were selected, with overall EEG classification performances between 61% and 70%. All parameters differed significantly between group 3 (severe) and groups 1 (normal-mildly abnormal) and 2 (moderate) EEGs (p < 0.001). Amplitude and discontinuity parameters were different between the 3 groups (p < 0.01) and were also the best predictors of clinical outcome. Conversely, pH and lactate did not differ between groups. DISCUSSION: This study provides quantitative EEG parameters that are complementary to visual analysis as early markers of neonatal HIE severity. These parameters could be combined in a multiparametric algorithm to improve their classification performance. The absence of relationship between pH lactate and HIE severity reinforces the central role of early neonatal EEG.

Sleep deprivation and Modafinil affect cortical sources of resting state electroencephalographic rhythms in healthy young adults.

OBJECTIVE: It has been reported that sleep deprivation affects the neurophysiological mechanisms underpinning the vigilance. Here, we tested the following hypotheses in the PharmaCog project (www.pharmacog.org): (i) sleep deprivation may alter posterior cortical delta and alpha sources of resting state eyes-closed electroencephalographic (rsEEG) rhythms in healthy young adults; (ii) after the sleep deprivation, a vigilance enhancer may recover those rsEEG source markers. METHODS: rsEEG data were recorded in 36 healthy young adults before (Pre-sleep deprivation) and after (Post-sleep deprivation) one night of sleep deprivation. In the Post-sleep deprivation, these data were collected after a single dose of PLACEBO or MODAFINIL. rsEEG cortical sources were estimated by eLORETA freeware. RESULTS: In the PLACEBO condition, the sleep deprivation induced an increase and a decrease in posterior delta (2-4 Hz) and alpha (8-13 Hz) source activities, respectively. In the MODAFINIL condition, the vigilance enhancer partially recovered those source activities. CONCLUSIONS: The present results suggest that posterior delta and alpha source activities may be both related to the regulation of human brain arousal and vigilance in quiet wakefulness. SIGNIFICANCE: Future research in healthy young adults may use this methodology to preselect new symptomatic drug candidates designed to normalize brain arousal and vigilance in seniors with dementia.

A 15-day course of donepezil modulates spectral EEG dynamics related to target auditory stimuli in young, healthy adult volunteers.

OBJECTIVE: To identify possible electroencephalographic (EEG) markers of donepezil's effect on cortical activity in young, healthy adult volunteers at the group level. METHODS: Thirty subjects were administered a daily dose of either 5mg donepezil or placebo for 15days in a double-blind, randomized, cross-over trial. The electroencephalogram during an auditory oddball paradigm was recorded from 58 scalp electrodes. Current source density (CSD) transformations were applied to EEG epochs. The event-related potential (ERP), inter-trial coherence (ITC: the phase consistency of the EEG spectrum) and event-related spectral perturbation (ERSP: the EEG power spectrum relative to the baseline) were calculated for the target (oddball) stimuli. RESULTS: The donepezil and placebo conditions differed in terms of the changes in delta/theta/alpha/beta ITC and ERSP in various regions of the scalp (especially the frontal electrodes) but not in terms of latency and amplitude of the P300-ERP component. CONCLUSION: Our results suggest that ITC and ERSP analyses can provide EEG markers of donepezil's effects in young, healthy, adult volunteers at a group level. SIGNIFICANCE: Novel EEG markers could be useful to assess the therapeutic potential of drug candidates in Alzheimer's disease in healthy volunteers prior to the initiation of Phase II/III clinical studies in patients.

Attention modulation during motor preparation in Parkinsonian freezers: A time-frequency EEG study.

OBJECTIVE: To investigate the cortical integration of attentional stimuli during motor preparation in parkinsonian patients with freezing of gait (FoG, n=12) or without freezing of gait (n=13), and in aged-matched healthy controls (n=13). We hypothesized that interference between attention and action in freezers would be revealed by differences in cortical modulation during this dual task. METHODS: Attention during step preparation was modulated by means of an auditory oddball discrimination task. EEG oscillations in different frequency bands were measured for the attentional stimulus and the motor stimulus. RESULTS: Over the 500ms following the sound, low-frequency power increased in all three groups. This was followed by a power decrease in mid-range frequencies after both target and standard sounds in the healthy controls and in the non-FoG group. In contrast, EEG oscillations in the beta band were impaired in the FoG group, who notably failed to display event-related desynchronization after perceiving the sound. CONCLUSIONS: An attentional stimulus was able to trigger event-related desynchronization before motor preparation in the non-FoG group but not in the FoG group. SIGNIFICANCE: In the FoG group, stimulus discrimination was maintained but the coupling between attention and motor preparation was impaired.

Effects of Stimulus-Driven and Goal-Directed Attention on Prepulse Inhibition of Brain Oscillations.

OBJECTIVE: Prepulse inhibition (PPI) is an operational measure of sensory gating. PPI of cortical response to a startling pulse is known to be modulated by attention. With a time-frequency analysis, we sought to determine whether goal-directed and stimulus-driven attention differentially modulate inhibition of cortical oscillations elicited by a startling pulse. METHODS: An electroencephalogram (EEG) was recorded in 26 healthy controls performing an active acoustic PPI paradigm. Startling stimuli were presented alone or either 400 or 1000 ms after one of three types of visual prepulse: to-be-attended (goal-directed attention), unexpected (stimulus-driven attention) or to-be-ignored (non-focused attention). We calculated the percentage PPI for the auditory event-related spectral perturbation (ERSP) of theta (4-7 Hz), alpha (8-12 Hz), beta1 (13-20 Hz) and beta2 (20-30 Hz) oscillations and changes in inter-trial coherence (ITC), a measure of phase synchronization of electroencephalographic activity. RESULTS: At 400 ms: (i) PPI of the ERSP of alpha, theta and beta1 oscillation was greater after an unexpected and a to-be-attended prepulse than after a to-be-ignored prepulse; and (ii) PPI of beta2 oscillations was greater after a to-be-attended than a to-be-ignored prepulse. At 1000 ms: (i) PPI of alpha oscillations was greater after an unexpected and a to-be-attended prepulse than after a to-be-ignored prepulse; and (ii) PPI of beta1 oscillations was greater after a to-be-attended than a to-be-ignored prepulse. The ITC values did not vary according to the type of prepulse. CONCLUSIONS: In an active PPI paradigm, stimulus-driven and goal-directed attention each have differential effects on the modulation of cortical oscillations.

Impulse Control Disorders in Parkinson's Disease are Associated with Alterations in Reward-Related Cortical Oscillations.

BACKGROUND: Impulse control disorders (ICDs) in Parkinson's disease (PD) are related to treatment with dopamine agonists, which is thought to deregulate the dopaminergic mesolimbic pathway and impair reward evaluation. EEG studies in healthy controls (HCs) have suggested that the increase in theta power observed after negative outcome is a marker of reward processing. OBJECTIVE: To compare outcome-locked, event-related spectral perturbation in a gambling task in PD patients with and without ICDs and in HCs. METHODS: Twelve PD patients with ICDs, 12 PD patients without ICDs and 14 HCs underwent EEG while performing a gambling task. The groups were compared in terms of (i) the peak EEG power in the theta (4-7 Hz), alpha (8-14 Hz) and beta (15-30 Hz) frequency bands between 200 and 500 ms after the outcome, and (ii) time-frequency plots at Fz, FCz and Cz. RESULTS: Positive outcomes were associated with greater theta power than negative outcomes in patients without ICDs and in HCs, but not in patients with ICDs. Patients with ICDs and HCs displayed greater theta power following unexpectedly high outcomes. HCs displayed greater beta power following high amplitude than low amplitude outcomes, whereas patients with ICD showed the opposite pattern. CONCLUSIONS: In PD, ICDs are associated with (i) weaker modulation of frontocentral theta power by reward valence, (ii) greater frontocentral theta power following unexpected, high outcomes, and (iii) a reversal of the effect of risk on beta oscillations. These observations are consistent with an impairment in prediction error computation in the medial prefrontal cortex.

Impaired Early Attentional Processes in Parkinson's Disease: A High-Resolution Event-Related Potentials Study.

INTRODUCTION: The selection of task-relevant information requires both the focalization of attention on the task and resistance to interference from irrelevant stimuli. A previous study using the P3 component of the event-related potentials suggested that a reduced ability to resist interference could be responsible for attention disorders at early stages of Parkinson's disease (PD), with a possible role of the dorsolateral prefrontal cortex (DLPFC). METHODS: Our objective was to better determine the origin of this impairment, by studying an earlier ERP component, the N2, and its subcomponents, as they reflect early inhibition processes and as they are known to have sources in the anterior cingulate cortex (ACC), which is involved together with the DLPFC in inhibition processes. Fifteen early-stage PD patients and 15 healthy controls (HCs) performed a three-stimulus visual oddball paradigm, consisting in detecting target inputs amongst standard stimuli, while resisting interference from distracter ones. A 128-channel electroencephalogram was recorded during this task and the generators of the N2 subcomponents were identified using standardized weighted low-resolution electromagnetic tomography (swLORETA). RESULTS: PD patients displayed fewer N2 generators than HCs in both the DLPFC and the ACC, for all types of stimuli. In contrast to controls, PD patients did not show any differences between their generators for different N2 subcomponents. CONCLUSION: Our data suggest that impaired inhibition in PD results from dysfunction of the DLPFC and the ACC during the early stages of attentional processes.

Attention modulates step initiation postural adjustments in Parkinson freezers.

BACKGROUND: In view of freezing of gait's circumstances of occurrence in Parkinson's disease, attentional resources appear to be involved in step initiation failure. Anticipatory postural adjustments (APAs) are essential because they allow unloading of the stepping leg and so create the conditions required for progression. Our main objective was to establish whether or not a change in attentional load during step initiation modulates APAs differently in patients with vs. without freezing of gait. METHODS: Three groups of 15 subjects were recruited: elderly people and parkinsonian patients with or without freezing of gait. Attention was modulated before step execution by means of an auditory oddball discrimination task with event-related potential recording. The primary endpoint was the occurrence of inappropriate APAs following the attentional task, i.e. APAs not followed by a step after an intercurrent auditory stimulus. RESULTS: In parkinsonian patients with freezing of gait, inappropriate APAs were recorded in 63% of the trials and were observed more frequently than in patients without freezing of gait (51%) and elderly controls (48%). Furthermore, inappropriate APAs in freezers were longer and more ample than in parkinsonian non-freezers and controls. Lastly, postural preparation was impaired in the parkinsonian patients. CONCLUSION: Our results indicate that allocation of attentional resources during step preparation influences the release of APAs differently in freezers and non-freezers. Modulating attentional load is partly responsible for triggering an inappropriate motor program. This difficulty in focusing attention or resisting interference may contribute (at least in part) to the gait initiation failure observed in parkinsonian freezers.

Effects of stimulus-driven and goal-directed attention on prepulse inhibition of the cortical responses to an auditory pulse.

OBJECTIVE: Inhibition by a prepulse (prepulse inhibition, PPI) of the response to a startling acoustic pulse is modulated by attention. We sought to determine whether goal-directed and stimulus-driven attention differentially modulate (i) PPI of the N100 and P200 components of the auditory evoked potential (AEP) and (ii) the components' generators. METHODS: 128-channel electroencephalograms were recorded in 26 healthy controls performing an active acoustic PPI paradigm. Startling stimuli were presented alone or either 400 or 1000ms after a visual prepulse. Three types of prepulse were used: to-be-attended (goal-directed attention), unexpected (stimulus-driven attention) or to-be ignored (non focused attention). We calculated the percentage PPI for the N100 and P200 components of the AEP and determined cortical generators by standardized weighted low resolution tomography. RESULTS: At 400ms, the PPI of the N100 was greater after an unexpected prepulse than after a to-be-attended prepulse, the PPI of the P200 was greater after a to-be-attended prepulse than after a to-be ignored prepulse. At 1000ms, to-be-attended and unexpected prepulses had similar effects. Cortical sources were modulated in areas involved in both types of attention. CONCLUSIONS: Stimulus-driven attention and goal-directed attention each have specific effects on the attentional modulation of PPI. SIGNIFICANCE: By using a new PPI paradigm that specifically controls attention, we demonstrated that the early stages of the gating process (as evidenced by N100) are influenced by stimulus-driven attention and that the late stages (as evidenced by P200) are influenced by goal-directed attention.

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

OBJECTIVE: Motor 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. METHODS: Using 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. RESULTS: The 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. CONCLUSION: This study provides evidence of central beta rhythms neuromodulation induced by MCS. SIGNIFICANCE: The restoration by MCS of defective cortical inhibition in patients with neuropathic pain is evoked.

Role of basal ganglia circuits in resisting interference by distracters: a swLORETA study.

BACKGROUND: The selection of task-relevant information requires both the focalization of attention on the task and resistance to interference from irrelevant stimuli. Both mechanisms rely on a dorsal frontoparietal network, while focalization additionally involves a ventral frontoparietal network. The role of subcortical structures in attention is less clear, despite the fact that the striatum interacts significantly with the frontal cortex via frontostriatal loops. One means of investigating the basal ganglia's contributions to attention is to examine the features of P300 components (i.e. amplitude, latency, and generators) in patients with basal ganglia damage (such as in Parkinson's disease (PD), in which attention is often impaired). Three-stimulus oddball paradigms can be used to study distracter-elicited and target-elicited P300 subcomponents. METHODOLOGY/PRINCIPAL FINDINGS: In order to compare distracter- and target-elicited P300 components, high-density (128-channel) electroencephalograms were recorded during a three-stimulus visual oddball paradigm in 15 patients with early PD and 15 matched healthy controls. For each subject, the P300 sources were localized using standardized weighted low-resolution electromagnetic tomography (swLORETA). Comparative analyses (one-sample and two-sample t-tests) were performed using SPM5® software. The swLORETA analyses showed that PD patients displayed fewer dorsolateral prefrontal (DLPF) distracter-P300 generators but no significant differences in target-elicited P300 sources; this suggests dysfunction of the DLPF cortex when the executive frontostriatal loop is disrupted by basal ganglia damage. CONCLUSIONS/SIGNIFICANCE: Our results suggest that the cortical attention frontoparietal networks (mainly the dorsal one) are modulated by the basal ganglia. Disruption of this network in PD impairs resistance to distracters, which results in attention disorders.

Deficit of sensorimotor integration in normal aging.

Sensorimotor performance declines with normal aging. The present study explored age-related changes in sensorimotor integration by conditioning a supra-threshold transcranial magnetic stimulation pulse with a peripheral nerve shock at different interstimulus intervals. Cortical motor threshold of the abductor pollicis brevis muscle, intracortical inhibition and facilitation were measured. We also assessed the influence of median nerve stimulation on motor cortex excitability at intervals which evoked short- and long-latency afferent inhibition (SAI and LAI, respectively) and afferent-induced facilitation (AIF). We observed a marked decrease of the long latency influence of proprioceptive inputs on M1 excitability in the elderly, with the loss of AIF and LAI. The SAI, motor thresholds and intracortical inhibition and facilitation were not age-related. Decreased sensorimotor performance with aging appears to be associated with a decrease in the influence of proprioceptive inputs on motor cortex excitability at longer intervals (probably via higher order cortical areas).

Use of swLORETA to localize the cortical sources of target- and distracter-elicited P300 components.

OBJECTIVE: Cognitive event-related potentials (especially P300) have long been used to explore attentional processes. The aim of this study was to identify the cortical areas involved in P300 generation during a selective attention task. METHODS: 128 channel electroencephalograms were recorded in 15 healthy controls performing a three-stimulus visual oddball paradigm, in order to identify distracter- and target-elicited P300 components. For each subject, the P300 sources were localized using standardized weighted low-resolution electromagnetic tomography (swLORETA). One sample and paired T-tests were performed using SPM5®. RESULTS: Common sources for both P300 components were observed within a large frontoparietal network, including the frontal eye field and dorsal parietal cortex (i.e. the attentional dorsal frontoparietal network). More inferior parietal areas, prefrontal and cingulate cortices (i.e. the attentional ventral frontoparietal network) were also involved in the generation of target-elicited P300. CONCLUSIONS: These results suggest that distracter- and target-elicited P300 are both generated by the dorsal frontoparietal network. Moreover, target processing recruits a specific ventral network. SIGNIFICANCE: Our data agree with the literature reports using other methods and should help to improve our knowledge of the cerebral networks underlying attentional processes.

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 wave's 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(R) 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.

Kinematic angular parameters in PD: reliability of joint angle curves and comparison with healthy subjects.

BACKGROUND: Most previous biomechanical studies of Parkinson's disease (PD) have been restricted to the description of spatiotemporal parameters and certain peak values for angular parameters. The reliability of joint angle curves and comparisons with control data are of major interest in PD, since variability in gait cycle timing is a feature of this pathology. METHODS: We used a video motion analysis system to record kinematic, spatiotemporal and angular parameters in 32 'off-drug' PD patients. The reliability of the patients' lower limb joint angle curves in the sagittal plane were analysed using the intra-class correlation coefficient (ICC), together with fast Fourier transform (FFT) analysis and hierarchical classification for discarding deviant curves. Lastly, we compared average curves (using a mixed model and the bootstrap method) for the less-affected and more-affected sides of PD patients and then compared the patient data with the results from 30 age-matched controls. RESULTS: The ICC-based procedure was easily applicable. Only 9.4% and 12.5% of the patients' hip and knee curves (respectively) were deemed to be unreliable. However, the PD patients' very high cycle-to-cycle variability in the sagittal plane ankle curves prevented us from applying to this joint. For the knee joint, the curves for the most disabled patients (who walked at below 0.5 m/s) were not reliable. We did not find any differences between the less and more disabled sides. The differences between patient and control curves concerned the double-support time during the stance phase and the time point for maximum knee flexion during the swing phase. Patients and controls differed in terms of the hip extension phase, with lower values in PD. CONCLUSION: We have developed the use of validated statistic tools for unambiguously comparing PD patients and controls in terms of joint angle curve differences.

Functional data analysis for gait curves study in Parkinson's disease.

In Parkinson's disease, precise analysis of gait disorders remains essential for the diagnostic or the evaluation of treatments. During a gait analysis session, a series of successive dynamic gait trials are recorded and data involves a set of continuous curves for each patient. An important aspect of such data is the infinite dimension of the space data belong. Therefore, classical multivariate statistical analysis are inadequate. Recent methods known as functional data analysis allow to deal with this kind of data. In this paper, we present a functional data analysis approach for solving two problems encountered in clinical practice: (1) for a given patient, assessing the reliability of the gait curves corresponding to the different trials (2) performing intra individual curves comparisons for assessing the effect of a therapy. In a first step, each discretized curve was interpolated using cubic B-splines bases in order to ensure the continuous character of data. A cluster analysis was performed on the smoothed curves to assess the reliability and to identify a subset of representative curves for a given patient. Intra individual curves comparisons were carried out in the following way: (1) functional principal component analysis was performed to describe the temporal structure of data and to derive a finite number of reliable principal components. (2) These principal components were used in a linear discriminant analysis to point out the differences between the curves. This procedure was applied to compare the gait curves of 12 parkinsonian patients under 4 therapeutic conditions. This study allowed us to develop objective criteria for measuring the improvements in a subject's gait and comparing the effect of different treatments. The methods presented in this paper could be used in other medical domains when data consist in continuous curves.

Relationship between intracerebral gamma oscillations and slow potentials in the human sensorimotor cortex.

Changes in sensorimotor rhythms (mu, beta and gamma) and movement-related cortical potentials (MRCPs) are both generated principally by the contralateral sensorimotor areas during the execution of self-paced movement. They appear to reflect movement control mechanisms, which remain partially unclear. With the aim of better understanding their sources and significance, we recorded MRCPs and sensorimotor rhythms during and after self-paced movement using intracerebral electrodes in eight epileptic subjects investigated by stereoelectroencephalography. The results showed that: (i) there is a strong spatial relationship between the late components of movement--the so-called motor potential (MP) and post-movement complex (PMc)--and gamma event-related synchronization (ERS) within the 40-60 Hz band, as the MP/PMc always occurred in contacts displaying gamma ERS (the primary sensorimotor areas), whereas mu and beta reactivities were more diffuse; and (ii) MPs and PMc are both generated by the primary motor and somatosensory areas, but with distinct sources. Hence, this could mean that kinesthesic sensory afferences project to neurons other than those firing during the pyramidal tract volley. The PMc and low gamma ERS represent two electrophysiological facets of kinesthesic feedback from the joints and muscles involved in the movement to the sensorimotor cortex. It could be suggested that gamma oscillations within the 40-60 Hz band could serve to synchronize the activities of the various neuronal populations involved in control of the ongoing movement.

Abnormal cortical mechanisms in voluntary muscle relaxation in de novo parkinsonian patients.

This study aimed at elucidating how the cortical mechanism underlying the preparation and the postmovement phase of voluntary hand muscle relaxation is affected in Parkinson's disease. Event-related mu and beta (de)synchronization (ERD/S) related to voluntary muscle contraction and relaxation were recorded in 16 untreated, akineto-rigid, predominantly hemiparkinsonian patients. The results were compared with data from 10 age-matched, healthy subjects. In the muscle relaxation task, the subject held the wrist in an extended position and then let the hand drop by voluntarily relaxing wrist extensor contraction, i.e., without any overt, associated muscle contraction. In the muscle contraction task, subjects performed a self-initiated brief wrist extension. A same pattern of ERD/S was observed in control subjects and parkinsonian patients performing the motor tasks with their less affected limb. In contrast, related to voluntary relaxation performed with the more affected limb, a delayed mu and beta ERD and a disappearance of beta ERS were revealed. These results demonstrate that the pattern of cortical oscillatory activity in a relaxation task is abnormal in parkinsonian patients. The authors suggest that this may be due to anomalous activity in inhibitory motor cortical systems and impaired sensorimotor integration of afferent inputs from muscle and joint receptors.

Intracerebral study of gamma rhythm reactivity in the sensorimotor cortex.

The generators and functional correlates of gamma oscillations within the sensorimotor cortex remain unclear. With the goal of locating the oscillations' sources precisely and then studying the relationship between oscillatory reactivity and ongoing movement, we recorded stereoelectroencephalograms with intracerebral electrodes in eight epileptic subjects awaiting surgical treatment. The sensorimotor cortex was free of lesions and was exhaustively explored with the electrodes. Subjects were asked to perform various self-paced movements contralateral to the exploration zone, brief and sustained, distal movements and a pointing movement. We used the event-related desynchronization method to quantify the reactivity of the 40-60-Hz band before, during and after the performance of movement. A very focused, event-related synchronization of gamma rhythms was found in all subjects. It was predominantly observed in the primary sensorimotor area and its distribution was consistent with the functional map established using electrical stimulations. Two different temporal patterns were observed, the event-related synchronization of gamma rhythms was related either to movement onset or to movement offset but was never recorded before movement. This observation suggests that gamma oscillations are more probably related to movement execution than to motor planning. The different patterns argue in favour of multiple functional roles; it has been shown that gamma oscillations may support the efferent drive to the muscles and here we show that they are also likely to be related to somatosensory integration. We therefore suggest that gamma oscillations in the 40-60-Hz band may support afferent sensory feedback to the sensorimotor cortex during the performance of movement.