Single cell activity in the ventral lateral thalamus of the unanesthetized monkey

Abstract

Spontaneous single cell activity was studied in the ventrolateral region of the thalamus in the unanesthetized monkey. The method used allowed recording in stereotaxic conditions as well as behavioral observations. Recorded cells were localized on histological sections. Patterns of discharge were analyzed and their relationship to the state of vigilance, posture, and movements were examined. Phasic changes in neuron firing patterns were shown to have a clear-cut behavioral counterpart. During alertness, with or without movements, the thalamic cells displayed a sustained but irregular firing associated with a desynchronized EEG. During states of relaxation and immobility, the cells tended to fire in high frequency bursts associated with high amplitude slow waves on the EEG. This burst activity was present only in the absence of movement. In the ventral part of the ventrolateral nucleus most of the cells could be activated by various natural stimuli, particularly those which provoked a quick muscle stretch. In general, the firing frequency of the cells was much greater if the animal made a spontaneous movement than if the same movement was made passively. On the basis of the reported findings it is suggested that ventrolateral neurons play an important role in the general adjustment of posture preliminary to voluntary movement.