[Transcranial magnetic stimulation].

The technique of transcranial magnetic stimulation of the motor cortex is a new neurophysiological examination of the central motor pathways. In clinical application a reduced MEP/M wave amplitude ratio had a higher correlation with hyperreflexia than did a delayed MEP onset latency. The inhibitory period (IP) which is a transient suppression of muscle action potentials following motor evoked potentials (MEP) by magnetic cortical stimulation is caused primarily by inhibitory process in the motor cortex, because the duration of IP did not depend on the amplitude of MEPs, MEP distribution over the motor cortex or severity of voluntary contraction. Furthermore, the IP was shorter and the amplitude of MEP was increased when ipsilateral motor cortex stimulation to the thenar muscle preceded the contralateral cortex stimulation. C response in a patient with familial essential myoclonus was significantly suppressed by the magnetic stimulation of the sensory cortex locally and during the IP. The uncrossed pyramidal tract was proved by motor cortex stimulation in a patient with hemorrhage in the right thalamus and internal capsule who showed a right hemiparesis. The enhancement of cortical SEP amplitudes (P23 and N30) were noted when the median nerve was stimulated at 50 msec following magnetic stimulation over the sensory cortex locally. SEPs by twin coil stimulation at thoracic and lumbar root levels are useful in detecting the lesions of spinal cord or roots. Sympathetic skin responses and sudomotor potentials are recorded easily by the neck magnetic stimulation, and are useful method for evaluating sympathetic nerve function.