Evoked Cortical Responses after the Stimulation of Ventrolateral Nucleus of Human Thalamus

Electrical low frequency stimulation of VL nucleus of the thalamus was performed with a bipolar stimulating electrode of 0.5 mm destance on 20 cases of extrapyramidal disorders. The evoked potentials were recorded with monopolar and bipolar scalp leads and displayed on paper as well as oscillographic records. The evoked potentials were noted mostly on the ispilateral side of fronto-parietal region in the regular suprathreshold stimulation, but bilateral evoked potentials with highest amplitude of the ipsilateral fronto-parietal region at the excessive suprathreshold stimulation. EEG of fronto-parietal region was analysed before, during and after the VL stimulation by means of Walter-type band-pass filter apparatus. It was interesting that clear waxing and waning phenomena were observed in the analysed band, which was concordant with the frequency of stimulation. When 6 cps stimulation was applied, the phenomena were obtained in the θ band. 10 cps in the a band. The evoked potentials were assumed as an augmenting response of the thalamic stimulation.