Evocation in paradoxical sleep of a hippocampal conditioned cellular response acquired during waking

Abstract

This experiment was a test of the possibility that a conditioned hippocampal response acquired during wakefulness could be evoked during paradoxical sleep (PS). After one session of habituation to a tone, waking rats underwent conditioning in four sessions during which the tone was used as the conditioned stimulus preceding a footshock. Pseudoconditioned animals received unpaired tone-shock presentations. There was a 24-h intersession interval. After each session, the same tone, never awakening the animal, was presented during PS phases. Hippocampal multiunit activity (MUA) was analyzed at each tone presentation during waking and during PS. Before conditioning, tone presentation did not affect MUA. During conditioning sessions, it elicited sustained increases in hippocampal discharge. When the tone was presented during postlearning PS, it induced a short-lasting increase in MUA. On the other hand, in the pseudoconditioned animals, hippocampal activity failed to show any change in response to the tone, whether during wakefulness or during PS. These results suggest that a behaviorally significant stimulus can be recognized during PS. © 1991, Psychonomic Society, Inc.. All rights reserved.