Changes in cortical responsiveness during transition from sleep to wakefulness

Abstract

In ence´phale isole´cats, the responsiveness of the visual cortex was assessed during the transition from sleep to wakefulness, and during the subsequent wakeful state, by measuring the amplitude of wave 4 of the cortical evoked response, following single shock stimulation of the optic radiation. In the drowsy or sleeping preparation (synchronized electrocortical activity) sudden arousal, by either peripheral or reticular formation stimulation, is accompanied by a marked but transient increase in cortical responsiveness. However, if the alerting stimulus is maintained and a permanent state of wakefulness achieved, this transient increase is followed by a decrease in cortical responsiveness, which then remains below slow wave sleep levels as long as the preparation remains awake. The early facilitation can be as short as 1 sec or last as long as 15–20 sec depending on various experimental conditions which are discussed. From these results and a review of current literature it is suggested that electrophysiological changes observed in the cortex of drowsy or sleeping animals, immediately after sudden arousal, may not be characteristic of the ‘awake’ cortex, but rather of the cortex in the process of being awakened. These two are apparently quite different physiological states.