Abnormal cortical processing of voluntary muscle relaxation in patients with focal hand dystonia studied by movement-related potentials.
In order to clarify the abnormality in cortical motor preparation for voluntary muscle relaxation of the hand in patients with focal hand dystonia, Bereitschaftspotentials (BPs) preceding voluntary muscle contraction and relaxation were recorded in eight patients (three with simple writer's cramp and five with dystonic writer's cramp), and were compared with those from 10 normal subjects. Voluntary muscle relaxation: after keeping the right wrist in an extended position for > 5 s, the subject let the hand drop by voluntarily terminating muscle contraction of the wrist extensor without any associated muscle contraction. Voluntary muscle contraction: the right wrist was flexed by voluntarily contracting the wrist flexor muscle. Scalp EEGs were recorded from 11 electrodes placed over the frontal, central and parietal areas. In the control group, the BP measured at the movement onset was maximal at the left central area (C1), and distributed predominantly over the left hemisphere equally in both the contraction and relaxation tasks. In the focal hand dystonia group, BP was maximal at C1 in the contraction task, whereas, in the relaxation task, it was maximal at the midline central area (Cz) and symmetrically distributed. At the left central area, the BP amplitude in the focal hand dystonia group was diminished significantly in the relaxation task compared with the contraction task (P < 0.05). The present results demonstrate for the first time that the cortical preparatory process for voluntary muscle relaxation, or motor inhibition, is abnormal in focal hand dystonia. (+info)
Bilateral subthalamic nucleus stimulation improves frontal cortex function in Parkinson's disease. An electrophysiological study of the contingent negative variation.
Parkinson's disease involves impaired activation of frontal cortical areas, including the supplementary motor area and prefrontal cortex, resulting from impaired thalamocortical output of the basal ganglia. Electrophysiologically, such impaired cortical activation may be seen as a reduced amplitude of the contingent negative variation (CNV), a slow negative potential shift reflecting cognitive processes associated with the preparation and/or anticipation of a response. Surgical interventions aimed at increasing basal ganglia-thalamic outflow to the cortex, such as electrical stimulation of the subthalamic nucleus with chronically implanted electrodes, have been shown to be effective in improving the clinical symptoms of Parkinson's disease. This study examined changes in cortical activity, as reflected in the CNV, associated with bilateral subthalamic nucleus stimulation in Parkinson's disease. The CNV was recorded from 10 patients with Parkinson's disease when on and off bilateral subthalamic nucleus stimulation, and was compared with the CNV of 10 healthy control subjects. Without subthalamic nucleus stimulation, Parkinson's disease patients showed reduced CNV amplitudes over the frontal and frontocentral regions compared with control subjects. With bilateral subthalamic nucleus stimulation, however, CNV amplitudes over the frontal and frontocentral regions were significantly increased. Results therefore suggest that impaired cortical functioning in Parkinson's disease, particularly within the frontal and premotor areas, is improved by subthalamic nucleus stimulation. (+info)
Medial frontal cortex in action monitoring.
Effective behavior requires continuous action monitoring. Electrophysiological studies in both monkeys and humans have shown activity in the medial frontal cortex that reflects dynamic control and monitoring of behavioral acts. In humans, the centromedial frontal cortex shows an electrical response within 100 msec of an error, the error-related negativity (ERN). The ERN occurs only when subjects are aware of making an error, suggesting that a critical factor may be self-monitoring of the action process. In the present study, we examined late responses in a deadline reaction time task, in which the subject becomes increasingly aware of making an error as the response becomes increasingly late. We found evidence of response conflict before errors defined by late responses but not before errors defined by incorrect responses. The results also show a linear increase in the amplitude of the ERN with increasingly late responses. These data suggest that frontal networks provide dynamic representations that monitor and evaluate the unfolding action plan. (+info)
Parallel information processing in motor systems: intracerebral recordings of readiness potential and CNV in human subjects.
We performed intracerebral recordings of Readiness Potential (RP) and Contingent Negative Variation (CNV) with simple repetitive distal limb movement in candidates for epilepsy surgery. In 26 patients (in Paris), depth electrodes were located in various cortical structures; in eight patients (in Brno), in the basal ganglia and the cortex. RPs were displayed in the contralateral primary motor cortex, contralateral somato-sensory cortex, and bilaterally in the SMA and the caudal part of the anterior cingulate cortices. CNVs were recorded in the same cortical regions as the RP, as well as in the ipsilateral primary motor cortex, and bilaterally in the premotor fronto-lateral, parietal superior, and middle temporal regions. In the basal ganglia, the RP was recorded in the putamen in six of seven patients, and in the head of the caudate nucleus and the pallidum in the only patient with electrodes in these recording sites. We suggest that our results are consistent with a long-lasting, simultaneous activation of cortical and subcortical structures, before and during self-paced and stimulus-triggered movements. The particular regions that are simultaneously active may be determined by the task context. (+info)
Effects of repetitive transcranial magnetic stimulation on movement-related cortical activity in humans.
Several lines of evidence suggest that low-rate repetitive transcranial magnetic stimulation (rTMS) of the motor cortex at 1 Hz reduces the excitability of the motor cortex and produces metabolic changes under and at a distance from the stimulated side. Therefore, it has been suggested that rTMS may have beneficial effects on motor performance in patients with movement disorders. However, it is still unknown in what way these effects can be produced. The aim of the present study is to investigate whether rTMS of the motor cortex (15 min at 1 Hz) is able to modify the voluntary movement related cortical activity, as reflected in the Beretischaftspotential (BP), and if these changes are functionally relevant for the final motor performance. The cortical movement-related activity in a typical BP paradigm of five healthy volunteers has been recorded using 61 scalp electrodes, while subjects performed self-paced right thumb oppositions every 8-20 s. After a basal recording, the BP was recorded in three different conditions, counterbalanced across subjects: after rTMS stimulation of the left primary motor area (M1) (15 min, 1 Hz, 10% above motor threshold), after 15 min of sham rTMS stimulation and following 15 min of voluntary movements performed with spatio-temporal characteristics similar to those induced by TMS. The tapping test was used to assess motor performance before and after each condition. Only movement-related trials with similar electromyographic (onset from muscular 'silence') and accelerometric patterns (same initial direction and similar amplitudes) were selected for computing BP waveforms. TMS- evoked and self-paced thumb movements had the same directional accelerometric pattern but different amplitudes. In all subjects, the real rTMS, but neither sham stimulation nor prolonged voluntary movements, produced a significant amplitude decrement of the negative slope of the BP; there was also a shortening of the BP onset time in four subjects. The effect was topographically restricted to cortical areas which were active in the basal condition, irrespective of the basal degree of activation at every single electrode. No changes in the tapping test occurred. These findings suggest that rTMS of the motor cortex at 1 Hz may interfere with the movement related brain activity, probably through influence on cortical inhibitory networks. (+info)
Multimodal EEG analysis in man suggests impairment-specific changes in movement-related electric brain activity after stroke.
Movement-related slow cortical potentials and event-related desynchronization of alpha (alpha-ERD) and beta (beta-ERD) activity after self-paced voluntary triangular finger movements were studied in 13 ischaemic supratentorial stroke patients and 10 age-matched control subjects during movement preparation and actual performance. The stroke patients suffered from central arm paresis (n = 8), somatosensory deficits (n = 3) or ideomotor apraxia (n = 2). The multimodal EEG analysis suggested impairment-specific changes in the movement-related electrical activity of the brain. The readiness potential of paretic subjects was centred more anteriorly and laterally; during movement, they showed increased beta-ERD at left lateral frontal recording sites. Patients with somatosensory deficits showed reduced alpha-ERD and beta-ERD during both movement preparation and actual performance. Patients with ideomotor apraxia showed more lateralized frontal movement-related slow cortical potentials during both movement preparation and performance, and reduced left parietal beta-ERD during movement preparation. We conclude that (i) disturbed motor efference is associated with an increased need for excitatory drive of pyramidal cells in motor and premotor areas or an attempt to drive movements through projections from these areas to brainstem motor systems during movement preparation; (ii) an undisturbed somatosensory afference might contribute to the release of relevant cortical areas from their 'idling' state when movements are prepared and performed; and (iii) apraxic patients have a relative lack of activity of the mesial frontal motor system and the left parietal cortex, which is believed to be part of a network subserving ideomotor praxis. (+info)
Disturbance of semantic processing in temporal lobe epilepsy demonstrated with scalp ERPs.
We investigated event-related potentials (N400, LPC and CNV) elicited in temporal lobe epilepsy (TLE) patients and control subjects from scalp electrodes, using a word-pair category matching paradigm. Each prime consisted of a Japanese noun (constructed from 2-4 characters of the Hiragana) followed by a Chinese character (Kanji) as the target, the latter representing one of five semantic categories. There were two equally probable target conditions: match or mismatch. Each target was preceded by a prime, either belonging to, or not belonging to, the same semantic category. The subjects were required to respond with a specified button press to the given target, according to the condition. We found RTs to be longer under the mismatch condition in both subject groups. The N400 amplitude was reduced in TLE subjects under both conditions, although LPC and CNV amplitudes showed no significant differences. These results suggest that scalp N400 is capable of demonstrating disturbance of semantic processing in TLE non-invasively. (+info)
Novelty-elicited mismatch negativity in patients with schizophrenia on admission and discharge.
OBJECTIVE: Given recent reports of differences between mismatch negativity (MMN) elicited by always novel sounds (novelty-elicited MMN) and that elicited by repeated rare deviants (conventional MMN), we investigated novelty-elicited MMN and P3a in patients with schizophrenia before and after a nonstandardized inpatient treatment. DESIGN: Electrophysiological and clinical assessment of patients on admission and discharge from hospital. Assessment of control subjects on 2 sessions. SETTING: Inpatient treatment in a psychiatric university hospital. SUBJECTS: 20 patients with schizophrenia and 21 healthy control subjects of similar age and sex. Selection of patients with first- to third-episode schizophrenia. OUTCOME MEASURES: Early and late component MMN amplitudes and latencies, P3a amplitudes and latencies, Positive and Negative Syndrome Scale (PANSS), Global Assessment of Functioning (GAF), Extrapyramidal Symptom Scale (EPS), Abnormal Involuntary Movement Scale (AIMS) and chlorpromazine equivalents. RESULTS: In patients with schizophrenia, novelty-elicited MMN was unimpaired on admission, and there was a statistically significant reduction of the late MMN component with treatment. Improvements in symptom expression were associated with increased latencies of the early MMN component. CONCLUSION: Results indicate differences in information processing between conventional and novelty-elicited MMN. Some components of the novelty-elicited MMN might be more state dependent than those of the conventional MMN. (+info)