Post-trial sleep in old rats trained for a two-way active avoidance task.

Nine male Wistar rats aged 27 months were trained for a two-way active avoidance task and tested for retention the following day. At variance with young adult rats, most of which succeed in mastering the task, all old rats displayed a large majority of freezing responses throughout the training and the retention sessions, thereby confirming the condition of learning impairment of aged rats. Comparison of baseline and post-trial sleep indicated the presence of a transient, but marked, increment in the average duration and total amount of post-trial slow-wave sleep followed by waking, and of a decrease in total amount of quiet waking. On the other hand, variables of paradoxical sleep and of slow-wave sleep followed by paradoxical sleep or by transition sleep did not show significant variations. Because these sleep variables are known to undergo significant variations in learning in young adult rats, the present data confirm that the latter effects are related to memory-processing events rather than to nonspecific effects of training. An additional outcome of training consisted in a marked post-trial decrement in the number of spike-wave discharges, which are known to occur in old rats during periods of quiet waking.