Electroencephalographic, behavioral, and single-unit effects produced by stimulation of forebrain inhibitory structures in cats

Abstract

The neuronal basis of EEG synchronization, sleep, and behavioral inhibition was studied in cats prepared chronically for forebrain stimulation and single-unit and EEG recording. Low-frequency stimulation to the orbital cortex, caudate nucleus, and the basal forebrain region all produced EEG synchronization and inhibition of ongoing operant behavior. Thresholds for behavioral inhibition were close to or slightly higher than thresholds for EEG synchronization. Cells in the cortex, thalamus, and hypothalamus were investigated during stimulation of the forebrain sites. There was a frequent parallel between unit effects and EEG slow-wave potentials recorded from the same electrode. A positive-going, slow potential was the usual concomitant of cellular inhibition. The data indicate that the three forebrain inhibitory regions have a convergence of synchronizing influences and that these influences are exerted upon cells sampled from all structures explored. There were no obvious differences in neuronal response as a function of cell location. The range of latencies of unit effects was from 1–24 msec, but in most cases the latencies were 5 msec or less, which suggests that the forebrain-influencing pathways are fairly direct rather than circuitous. It was proposed that the forebrain influences which produce sleep and behavioral inhibition are due not simply to a neuronal shutdown of the reticular-activating system but to direct and widespread effects.