Abolition of several forms of cortical synchronization during blockade in the inferior thalamic peduncle.

Abstract Six chronic cat preparations were each implanted as follows: (1) A stimulating electrode was implanted in nucleus centralis medialis thalamicus for eliciting recruiting responses. (2) A stimulating electrode was implanted in nucleus ventralis lateralis thalamicus for producing augmenting responses. (3) A stimulating electrode was implanted in the head of the caudate nucleus for creating caudate spindles. (4) Transcortical recording electrodes were implanted in several frontal regions (anterior sigmoid, coronal and anterior lateral gyri) and in various posterior sites (anterior suprasylvian and posterior lateral gyri), and an indifferent electrode was implanted in the frontal sinus bone. (5) Bipolar cryoprobes were implanted in the region of the inferior thalamic peduncle (ITP) medial to the internal capsule and rostral to the thalamus. The model experimental preparation was one in which recruiting responses were abolished or markedly reduced by cryogenic blockade in the ITP, but augmenting responses were unaffected. Three control animals had identical stimulating and recording electrodes but had cryoprobes placed which were either lateral, dorsal or anterior to the critical region of the ITP. Several different forms of cortical synchronization were produced as follows: (1) barbiturate spindles by intravenous injections of sodium pentobarbital (35 mg/kg body weight); (2) atropine spindles by intravenous injection of atropine sulfate (1 mg/kg body weight); (3) THC spindles by intraperitoneal injection of marijuana extract (17% delta-1-tetrahydrocannabinol; 16 mg/kg body weight); (4) sleep spindles by sleep deprivation; (5) caudate spindles by single shock stimulation of the head of the caudate nucleus. Cryogenic blockade or permanent lesion in the region of the ITP sufficient to abolish recruiting responses but not to affect augmenting responses had the following effects on these various forms of cortical synchronization: (1) A 12 c/sec component of barbiturate spindles was abolished. (2) A 12 c/sec component of atropine spindles was abolished. (3) The sustained 12 c/sec synchronization of THC spindles was abolished. (4) A 12 c/sec component of sleep spindles was abolished. (5) Caudate spindles were abolished, and the short-latency, surface-positive response to the single shock was enhanced. None of the control animals showed any of these effects. All of the abolished components had fairly smooth wave forms, and the components remaining during blockade had complex wave forms with inflections in them. It was interpreted that the abolished components were the type II spindles of Spencer and Brookhart (1961b), since they had relatively smooth wave forms and spindle shapes and were abolished together with recruiting responses. The role of this form of cortical synchronization in higher nervous activities is not known, but blockade in the non-specific thalamo-cortical system sufficient to abolish the synchronization also renders an animal unable to perform certain learned tasks associated with selective perception, expectancy and attention.