Thalamo-cortical systems regulating spindle bursts and recruiting responses. II. Effect of thalamic lesions.

The effects of thalamic lesions on recruiting responses and spindle bursts have been studied in 12 cats immobilized with gallamine. Recruiting responses were elicited by stimulation of the midline thalamic nuclear complex. Spindle bursts were produced by lesions in the mesencephalic tegmentum. Recruiting responses and spindle bursts were recorded from the cortex and thalamus. The effect of thalamic lesions on such spontaneous and induced potentials was evaluated by making lesions anteriorly in the rostral pole of the thalamus, medially in the midline thalamic nuclear group, and laterally in the primary and association nuclei of the thalamus. 1. Small, anterior, thalamic lesions blocked spindle bursts and recruiting responses both at the cortex and in the thalamus. 2. Massive, medial, thalamic lesions blocked spindle bursts in the suprasylvian cortex, but did not affect either frontal cortex spindle bursts or frontal and thalamic recruiting responses induced by stimulation of N. ventralis anterior. 3. Massive, lateral, thalamic lesions including specific relay and association nuclei, failed to block spontaneous spindles and recruiting responses in frontal cortex and midline thalamic nuclei. It has been postulated that the rostral pole of the thalamus constitutes an important part of the thalamic portion of a thalamo-orbitocortical system which mediates and regulates electrocortical synchronization as manifested in spindle bursts, recruiting responses and synchronized wave-like potentials.