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Query: UMLS:C0027066 (myoclonus)
 4,275 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have done a few physiological studies on six patients with cortical reflex myoclonus and three patients with unilateral focal dystonia caused by a discrete cerebrovascular lesion in the basal ganglia. The silent period after magnetic cortical stimulation was normal or slightly prolonged in all the patients with cortical myoclonus. In contrast, in patients with focal dystonia, it was shortened in the muscles on the contralateral side to the lesion, whereas normal in duration on the ipsilateral side. Excessive inputs from the disinhibited supplementary motor cortex to the primary motor cortex due to a lesion of the basal ganglia must cause this shortening in the dystonic hand muscles. Excitability recovery of the motor cortex after hypersynchronous activation by magnetic stimulation should be prolonged in the myoclonic patients. Cortico-cortical inhibition of the motor cortex studied with paired magnetic stimulation technique was disturbed in both the patients with myoclonus and those with dystonia. This result suggested that the disinhibition of the motor cortex is present in both disorders. Based on these results, we conclude that the motor cortex is similarly disinhibited in both disorders, but recovery function from hypersynchronous activation is different between these two groups.
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PMID:[Electromyographic analysis of cortical myoclonus and focal dystonia]. 875 6

The method of magnetic transcranial stimulation of the motor cortex produces both excitatory and inhibitory effect. Definition of excitability and inhibitory threshold represents clinically useful indicator. In order to reduce variability of the thresholds, it is important to notice mental activity, posture, type of magnetic stimulator, involuntary movement, muscle tonus and age. Excitability threshold was elevated in patients with stroke and reduced in patients with epilepsy. Enhancement of motor excitability by subthreshold magnetic stimulation of the motor cortex prior to voluntary movement was observed during simple reaction time measurement. Reaction time can be divided into a period of resting condition and the premotion facilitatory effect in the 50 approximately 60 ms after the target stimuli. In patients with Parkinson's disease, the prolongation of reaction time is due to a prolongation of a period of premotion facilitatory effect. Jerk-locked MEP is a useful technique to evaluate a change of motor excitability after voluntary or involuntary movement. To record jerk-locked MEP, magnetic stimulation of the motor cortex is delivered at varying intervals after the onset of the EMG activity. We classified the cortical reflex myoclonus into three forms according to changes of motor excitability after C reflex.
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PMID:[Analysis of cortical excitation and inhibition using transcranial magnetic stimulation]. 875 48

Movement disorders are physiologically studied based on three principles; 1. relation between movements and brain activities, 2. excitability and inhibitory mechanisms of motor cortices, and 3. sensorimotor integration. Regardless of voluntary or involuntary movements, the study on how the movement in question is related to brain activities provides an important information as to its pathophysiology. This can be studied by jerk-locked averaging of electroencephalogram or magnetoencephalogram in case of involuntary movements and movement-related cortical potentials for voluntary movements, change of cortical rhythmic activities in relation to movement (event-related desynchronization or synchronization), cortico-muscular coupling(coherence), and neuroimaging techniques such as PET, SPECT and fMRI. Excitability and inhibitory mechanisms of motor cortices can be studied by applying transcranial magnetic stimulation. Positive and negative myoclonus of cortical origin is related to abnormal hyperexcitability of the positive and negative components, respectively, of the primary motor cortex (M1). Focal dystonia is associated with impairment of inhibitory mechanisms in M1. The simplest form of abnormal sensorimotor integration is cortical reflex myoclonus. In the choice reaction time task, contingent negative variation is reduced in a task-specific way in focal dystonia. Effect of movement on somatosensory processing (gating) is abnormal immediately before the movement onset in focal dystonia, again in a task-specific way. Daily activities like gait can be studied by SPECT which does not require fixation of the subject's head during the task performance.
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PMID:[Clinical neurophysiology of movement disorders]. 1278 75