MODULATION OF POSTURAL WRIST TREMORS BY MAGNETIC STIMULATION OF THE MOTOR CORTEX IN PATIENTS WITH PARKINSONS-DISEASE OR ESSENTIAL TREMOR AND IN NORMAL SUBJECTS MIMICKING TREMOR

The effect of magnetic brain stimulation on postural wrist tremor was studied in 10 patients with Parkinson's disease, 12 with hereditary es sential tremor, and 10 normal subjects who mimicked tremor by making r apid alternating wrist movements. In all patients and normal subjects, magnetic brain stimulation over the contralateral motor cortex at an intensity approximately 10% above threshold produced the following seq uence of events: (1) a small direct electromyographic (EMG) response, followed by (2) suppression of the rhythmic EMG activity responsible f or the tremor, before (3) reappearance of the tremor time-locked to th e stimulus. It is concluded that magnetic brain stimulation over the m otor cortex can modulate the oscillatory mechanisms responsible for th e generation of postural tremors. Group analysis revealed that the tim e to reappearance of rhythmic EMG activity varied significantly with t he period of parkinsonian postural tremors, but not with the period of essential or mimicked tremors. Magnetic stimulation also significantl y shortened the period of parkinsonian postural tremors, but did not i nfluence the period of essential or mimicked tremors. These behavioral differences indicate differences in the pathophysiological mechanisms underlying parkinsonian postural tremor and essential tremor.