Etienne Labyt

Basic mechanisms of central rhythms reactivity to preparation and execution of a voluntary movement: a stereoelectroencephalographic study.

OBJECTIVE To localize the sources of mu, beta and gamma rhythms and to explore the functional significance of their reactivity. METHODS We used the method of quantification of event-related desynchronization (ERD) and synchronization (ERS) to analyze the reactivity of intracerebral rhythms recorded in stereoelectroencephalography within the sensorimotor areas during the preparation and the execution of a simple self-paced hand movement. We recorded 3 epileptic subjects who were explored before a surgical treatment. RESULTS An ERD of mu and beta rhythms has been recorded before the movement onset in the precentral gyrus, spreading then to the postcentral gyrus and to the frontal medial cortex. The frontal lateral cortex was inconstantly involved during the movement. The movement offset was followed by an important and focused beta ERS which was found within the pre- and post-central gyrus and the frontal medial cortex. Within the beta band, we observed several narrower bands with different reactivities and locations. Focused gamma reactivity was also found in the precentral and postcentral gyri. CONCLUSIONS The reactivities of mu and beta rhythms are different but their locations overlap. Mu ERD is a diffuse phenomenon that reflects the activation of all the sensorimotor areas during a simple movement. Beta band is likely to be composed of different rhythms with different functional significance. The primary motor area seems to contain two distinct areas with different reactivity to the movement preparation and execution.

Relationship between event-related beta synchronization and afferent inputs: Analysis of finger movement and peripheral nerve stimulations

OBJECTIVE We compared beta synchronization associated with voluntary finger movement with beta synchronization produced by sensory stimulation, in order to better understand the relationship between event-related beta synchronization (ERS) and the different afferent inputs. METHODS Twenty-four subjects performed an index finger extension. They also received three types of electrical stimulation (cutaneous stimulation of the index finger, single and repetitive stimulation of the median nerve). An EEG was recorded using 38 scalp electrodes. Beta ERS was analyzed with respect to movement offset and the stimulus (or the last stimulus in the series, for repetitive stimulation). RESULTS Median nerve stimulation and finger extension induced more intense beta ERS than cutaneous stimulation. The magnitude of beta ERS induced by movement or by single median nerve stimulation were not different but post movement beta synchronization duration was longer than beta ERS induced by single median nerve stimulation and cutaneous stimulation. CONCLUSIONS This study demonstrates that beta ERS depends on the type and quantity of the afferent input. SIGNIFICANCE This work reinforces the hypothesis of a relationship between beta ERS and processing of afferent inputs.

Role of hypokinesia and bradykinesia in gait disturbances in Huntington's disease : A biomechanical study

ObjectiveTo evaluate specific patterns of locomotion in Huntingtons disease (HD) and notably the respective roles of hypokinesia (i. e. a decrease in the amplitude of movement) and bradykinesia (i. e. difficulty in executing a movement, slowness) in gait disturbance.MethodsKinematic, spatial (stride length, speed), temporal (cadence, speed, and stride time) and angular gait parameters (joint ankle range) were recorded in 15 early–stage HD patients by means of a video motion analysis system and then compared with 15 controls and 15 Parkinsons disease (PD) patients. Hypokinesia was studied in terms of both spatial (decrease in stride length) and angular gait parameters (decrease in joint ankle range), whereas hyperkinesia was characterized by an increase in joint ankle range. Bradykinesia (defined by a decrease in gait velocity) was also assessed in terms of temporal parameters (cadence, stride time). We studied the influence of clinical symptoms (motor dysfunction, chorea, overall disability and cognitive impairment) and the CAG repeat number on gait abnormalities.Resultswe observed a clear decrease in gait speed, a decrease in cadence and an increase in stride time (i. e. bradykinesia) for HD, with significant intra–individual variability. Cadence remained normal in PD. In HD, there was no evidence for a clear decrease in stride length, although the latter is a characteristic feature of hypokinetic gait (such as that observed in PD). Angle analysis revealed the coexistence of hyperkinesia and hypokinesia in HD, which thus participate in gait abnormalities. Gait speed in HD was correlated to the motor part of the UHDRS.ConclusionGait in HD is mainly characterized by a timing disorder: bradykinesia was present, with severe intra–individual variability in temporal gait parameters.

Influence of aging on cortical activity associated with a visuo-motor task

The aim of this study was to determine how cerebral aging influences the pattern of cortical oscillatory activity when a targeting movement with visual control is planned. Changes in cortical oscillatory activity were assessed by recording the event-related (de)synchronization (ERD/S) of micro and beta rhythms. Young and elderly subjects performed a distal movement, a proximal movement and a visuo-guided targeting movement. Our results demonstrated an increase in micro ERD over ipsilateral regions and showed the spatial extent of micro ERD over parietocentral and parietal regions during motor planning in elderly subjects compared to young ones. After the movement, the beta ERS was significantly modified (a decrease in slope and amplitude) in elderly subjects. The most pronounced age-related changes in ERD/S pattern were observed for the targeting movement. Our results suggest that motor planning is less efficient in elderly subjects. This deficit might result from impaired parietal integrative function and/or changes in inputs from subcortical structures. Subsequently, the changes observed in the post-movement phase might reflect a decrease in (reafferent) sensory inputs and hence impaired their input processing.

Changes in oscillatory cortical activity related to a visuomotor task in young and elderly healthy subjects

OBJECTIVE In order to better understand the spatio-temporal interaction of the activated cortical areas when the movement is visuo-guided and to assess the age effect on the spatio-temporal pattern of cortical activity, we have compared a proximo-distal movement with visual-motor control and hand-eye coordination (targeting movement) with a distal and a proximal movement. METHODS Brains electrical activity was studied using the analysis of event-related (de)synchronizations (ERD/S) of cortical mu and beta rhythms in 17 subjects, 8 young and 9 elderly subjects. RESULTS In both populations, we found an earlier and broader mu and beta ERD during the preparation of the targeting movement compared to distal and proximal movements, principally involving the contralateral parietal region. During the execution, a spreading over the parietocentral region during proximal movement and over the parietal region during targeting movement was observed. After the execution of proximal and targeting movements, a wider and higher beta ERS was observed only in the young subjects. In the elderly subjects, our results showed a significant decrease of beta ERS during the targeting task. CONCLUSIONS These results suggest there was a larger recruitment of cortical areas, involving notably the parietal cortex when the movement is visuo-guided. Moreover, cerebral aging-related changes in the spatio-temporal beta ERS pattern suggests an impaired sensory integration.

Anticipatory postural adjustments associated with arm movement in Parkinson’s disease: a biomechanical analysis

Objective: To study anticipatory postural adjustments (APAs) in Parkinson’s disease (PD) via a biomechanical analysis, including vertical torque (Tz). Methods: Ten patients with PD (in the “off-drug” condition) and 10 age matched controls were included. While standing on a force platform, the subject performed a right shoulder flexion in order to grasp a handle in front of him/her, under three conditions (all at maximal velocity): movement triggered by a sound signal and loaded/non-loaded, self-paced movement. The anteroposterior coordinates of the centre of pressure (COP) and Tz were calculated. Results: A group effect was observed for Tz and COP in patients with PD (compared with controls): the maximal velocity peak appeared later and the amplitude of the COP backward displacement and the area of the positive phase of Tz were lower, whereas the duration of the positive phase of Tz was greater. Interaction analysis showed that the area of Tz was especially affected in the triggered condition and the loaded, self-paced condition. The onset of the COP backward displacement was delayed in the triggered condition. Conclusion: Our biomechanical analysis revealed that patients with PD do indeed perform APAs prior to unilateral arm movement, although there were some abnormalities. The reduced APA magnitude appears to correspond to a strategy for not endangering postural balance.

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.

Oscillatory cortical activity related to voluntary muscle relaxation: Influence of normal aging

OBJECTIVE In this study we aimed to investigate if there are age-related differences in cortical oscillatory activity induced by self-paced muscular pure relaxation in comparison with muscle contraction as reference movement. METHODS Event-related (de)synchronization (ERD/ERS) have been recorded related to voluntary muscle contraction and relaxation in 10 young and 10 elderly right-handed healthy subjects. The muscle relaxation task consisted in a voluntary relaxation of maintained wrist extension without any overt, associated muscle contraction. The muscle contraction task corresponded to a self-initiated brief wrist extension. RESULTS In elderly subjects compared to young ones, mu and beta ERD preceding muscular relaxation was more widespread, beginning significantly earlier over contralateral frontocentral and parietocentral regions (p<0.05) as well as over ipsilateral regions (p<0.05). The beta synchronization was significantly attenuated (p<0.05). CONCLUSIONS These results suggest an alteration of inhibitory motor systems and an altered post-movement somesthetic inputs processing with normal aging. These alterations were accompanied by compensatory mechanisms. SIGNIFICANCE These age-related alterations during different phases of muscle relaxation could participate to explain global sensorimotor slowing observed with normal aging.

Subthalamic stimulation influences postmovement cortical somatosensory processing in Parkinson's disease

In Parkinsons disease, poor motor performance (resulting primarily from abnormal cortical activation during movement preparation and execution) may also be due to impaired sensorimotor integration and defective cortical activity termination of the ongoing movement, thus delaying preparation of the following one. Reduced movement‐related synchronization of the beta rhythm in Parkinsons disease compared to controls has been put forward as evidence for impaired postmovement cortical deactivation. We assessed the effects of subthalamic deep brain stimulation and l‐dopa on beta rhythm synchronization over the premotor and primary sensorimotor cortex. Ten advanced patients performed self‐paced wrist flexion in four conditions according to the presence or not of stimulation and l‐dopa. Compared to without treatment, the motor score improved by ≈ 60%; the beta synchronization was present over the contralateral frontocentral region and increased significantly over the contralateral central region under stimulation and under l‐dopa, with a maximal effect when both treatments were associated. Our advanced patients displayed very focused and attenuated beta rhythm synchronization which, under stimulation, increased over the contralateral premotor and primary sensorimotor cortex. Stimulation and l‐dopa both partly restored postmovement cortical deactivation in advanced Parkinsons disease, although the respective mechanisms probably differ. They may improve bradykinesia and cortical deactivation by reestablishing movement‐related somatosensory processing at the end of the movement through the basal ganglia into the cortex.

Motor preparation is more impaired in Parkinson's disease when sensorimotor integration is involved

OBJECTIVE This study aimed to investigate changes in spatio-temporal, event-related (de)synchronization (ERD/ERS) patterns recorded with respect to the more akinetic versus the less akinetic side during performance of a visuo-guided targeting movement when compared to an index finger extension. METHODS Twelve de novo parkinsonian patients were recorded. ERD/ERS in mu and beta frequency bands was computed from 21 source derivations. RESULTS When the index finger extension was performed with the less akinetic limb, mu ERD focused over contralateral central region appeared 2 s before movement. With the targeting movement, additional pre-movement mu ERD was observed over the parietal region, as well as earlier ipsilateral mu ERD. When the same movements were performed with the more akinetic limb, we observed delayed mu ERD over contralateral regions, earlier ipsilateral mu ERD and a lack of contralateral parietal mu ERD before the targeting movement. Following index finger extension for the less akinetic limb, a focused contralateral central beta ERS was recorded, increasing and spreading after the targeting movement. In contrast, for the more akinetic limb, beta ERS was dramatically attenuated and remained unchanged after the targeting movement. CONCLUSIONS These results confirm the fact that motor programming is delayed, and provide some insight into what may well be impaired sensorimotor integration in Parkinsons disease.