Cortical control of thalamic spindle waves

Abstract

The EEG activity of the thalamus was studied in acute cat preparations in which the diencephalon was deprived of all neocortical and most archicortical and striatal connections. Waves (8–12/sec) waxing and waning, similar to electrocortical spindles, were recorded in all cases. They persisted after interruption of the interhemispheric commissures, and were enhanced by mesencephalic transection, lesion of the optic chiasma or injection of a small dose of barbiturate (3 mg/kg, iv). Spindles occurred more than twice as frequently in a decorticate thalamus than in the thalamus of a contralateral intact hemisphere. Producing lesions in the region of the inferior thalamic peduncle (ITP) in an intact hemisphere abolished both thalamic and cortical spindles. This effect persisted after complete mesencephalic transection, but the spindles reappeared after complete decortication. It is postulated that EEG spindles are basically thalamic in origin and that their occurrence is controlled by antagonistic corticothalamic influences which operate independently from influences of the caudal brain stem.