Unitactivity connected with movement initiation and arousal situations recorded from the ventrolateral nucleus of the human thalamus.

Abstract

A total of 21 microelectrode recordings from the human thalamus were made during stereotactic operations on patients with Parkinson's disease, intention tremor and dystonia. The electrode consisted of a 0.5 mm laquered tungsten wire having an electrolytically sharpened tip of about 5 μ. The electrode was inserted into the thalamus coaxially in a guiding probe the distal uninsulated ring of which served as the indifferent electrode. The probe was fitted to the standard Riechert stereotactic crown. All but one of the patients were fully conscious during the study. Activity of both single and multiunit type was obtained from the ventrolateral (VL) nucleus. Spontaneous irregular and spontaneous rhytmic activities with different frequencies were recorded. Of special interest were the rhythms within the same range as the Parkinsonian tremor. The results of previous investigations were largely confirmed. The earlier reported phenomena connected with the initiation of voluntary motor acts were recorded but the results did not show the previously indicated close correlation between activated thalamic units and certain muscle groups. Muscle vibration causing local tonic vibration reflexes and a potentiation of the Parkinsonian tremor had no obvious effect upon the firing patterns of units in the VL nucleus. Marked changes in the activity of the VL neurons were often observed in response to arousal stimuli of different types. Anything happening suddenly to the subject could produce either intense bursts of single and multiunit activity, or interruption of spontaneous activity or changes in regularity of firing. Responses of this sort, which were characterized by rapid habituation, were seen most frequently in patients with intention tremor and dystonia. The findings suggest that in patients of this type the midbrain reticular activating system exerts an abnormal influence on the synaptic events in the ventrolateral nucleus.