[Analysis of cortical excitation and inhibition using transcranial magnetic stimulation]

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.