STEREOTAXIC surgery for the so-called extrapyramidal motor disorders offers an opportunity to study the neurophysiology of deep-lying structures of the human brain. Of these the ventrolateral nucleus (VL) and its neighboring area of the thalamus is especially important and is the concern of the present study.
Low frequency stimulation of VL elicits repetitive waves in the ipsilateral cortical motor area.1 This phenomenon permits precise delineation of that nucleus prior to the surgical lesion. From the human VL nucleus a sub-VL area has been differentiated.2 A small circumscribed area behind the VL and rostral to the posterior nucleus has been related to the mechanism of tremor. Destruction of this area reduces or abolishes tremor whereas stimulation increases it in parkinsonian patients.3 Microelectrode studies in this area have shown the unit activity firing in a group fashion, sometimes corresponding in frequency to the tremor.4 In this study