Reactivation of interference during sleep does not impair ongoing memory consolidation.

Memory consolidation during sleep is assumed to rely on the repeated reactivation of newly encoded memories particularly during slow wave sleep (SWS). It has been proposed that reactivated memories during sleep - like during wakefulness - undergo a labilisation process, enabling the strengthening and integration of new memories into pre-existing networks. Here, we tested this idea by introducing interference directly during sleep in the reactivation/consolidation phase. We predicted that cueing interfering memories during sleep would impair the consolidation of recently learned memories. Participants learned a visuo-spatial memory task before they were allowed to sleep for 40 min. During sleep, and particularly during SWS, subjects were presented with interference via odour cueing (compared to a no interference vehicle condition). In contrast to our hypothesis, cueing of the interference during sleep did not impair consolidation of the newly learned memories: odour and vehicle conditions did not differ in memory recall after sleep. On the contrary, subjects even displayed significantly fewer intrusions from the interference during memory recall when the odour was presented during sleep. These findings suggest that interference presentation during sleep does not disrupt endogenous memory consolidation, but might even facilitate pattern separation and memory stabilisation through generalisation processes.