Sequential hypothesis of sleep function. V. Lengthening of post-trial SS episodes in reminiscent rats.

Rats failing to learn a two-way active avoidance task during the training session were tested for performance the following day. One group of rats maintained its low level of avoidances (non improving or NI rats), while the remaining rats dramatically improved their avoidance score (improving or I rats). EEG recording during the posttrial period demonstrated significant variations in the sleep structure of I rats, in comparison with NI rats. The main change consisted in an increase in the average duration of the episodes of slow wave sleep followed by wakefulness or by paradoxical sleep. These variations occurred in the third hour of the posttrial period, while an increment in the amount of PS was observed in the sixth hour. In I rats, but not in NI rats, comparable variations emerged from the comparison of baseline sleep (determined the day before training) with posttrial sleep. The data are in agreement with the main postulate of the sequential hypothesis of sleep function which attributes a primary role to slow wave sleep in the processing of newly acquired memories.