Improvement of learning by cueing during postlearning paradoxical sleep

Rats were submitted to an active avoidance conditioning in a shuttle box with slight ear shocks used as conditioned stimulus (CS) preceding a foot shock. Three conditioning sessions were performed with a 24 h intersession interval. Animals were divided into 3 groups. After each session, the first group received the CS as cue during the first 6 phases of paradoxical sleep (PS) following learning. The second group received the CS as cue during 6 periods of wakefulness. The third group received no cue. Animals cued during PS showed a significant improvement in performances. The effect of cueing during the awake state appeared to be marginal compared to the clear-cut effects when the cue was presented during PS. A control experiment showed that the same ear shocks presented during PS were ineffective when they were not associated with the learning task (in this experiment a tone was used as CS during conditioning). These results are discussed in terms of memory reactivation during postlearning paradoxical sleep.