Physiologically defined VIM nucleus. Its special reference to control of tremor.

In the course of stereotactic surgery for some 100 parkinsonian patients, correlative study of recording and stimulation has been done in and around the thalamic nucleus ventralis intermedius (VIM) under local anesthesia. The VIM nucleus is roughly identified either by the increase of neural noise level or radiological measurement. More accurately, in the thus identified VIM, sensory neurons related to kinesthetic sense of the contralateral extremity were found in about half of the cases. Electrical stimulation of this point at threshold intensity produced paresthesia on the contralateral area around its receptive field. With increased stimulus intensity, increment of grouping discharge in EMG of that part was pertinent in the majority of cases. A small localized lesion at such a thalamic point was shown to be quite effective for alleviation of tremor without any neurological, especially sensory, deficit.