Effects of state of arousal on click responses in the mesencephalic reticular formation

Abstract

Click responses in the mesencephalic reticular formation, the cochlear nucleus and the primary auditory cortex were studied during sleep and wakefulness in cats with implanted electrodes. The following observations were made: 1. 1. During the quiet waking state, click responses in the mesencephalic reticular formation consisted of slow waves of up to 150 μV. amplitude which persisted undiminished after more than one thousand consecutive clicks. 2. 2. During sleep with EEG slow waves, habituation of responses in the mesencephalic reticular formation occurred after only 5–10 clicks. Responses became variable and mean amplitude of responses decreased to about 50 per cent of response size in waking animals. 3. 3. During sleep with low voltage fast EEG activity, there was almost complete suppression of brain stem responses to repeated clicks. 4. 4. Response in the cochlear nucleus did not vary with changes in state of arousal. 5. 5. Click responses on primary auditory cortex persisted during sleep except for a decrease in the late slow wave components of the response. The results suggest that during natural sleep there is depression of activity in the non-specific afferent system, while activity in primary auditory pathways remains unchanged. The depression of activity in the nonspecific afferent system during sleep differs in several respects from that observed during the anesthetic state.