The effects of targeted reactivation on memories cued once or multiple times during a nap.

During sleep, memory traces are reactivated and consolidated into long-term memory. Discrete reactivation events involve coordinated activity between the hippocampus and neocortex. In this study, we examined whether the number of reactivation events directly translates to benefits to memory. To test this, we used targeted memory reactivation, a technique to selectively bias reactivation for certain memories by presenting non-invasive sensory cues. Participants (N = 31) completed a computerized object-location task, in which 60 images were presented along with related sounds. During non-REM sleep, 40 of these sounds were presented either once (20 sounds) or five times (20 sounds) in an interleaved fashion. Participants then completed another task designed to interfere with the previously encoded spatial memories, before being tested again on the initial object positions. The results showed no significant performance benefits for cued objects regardless of the number of sound presentations. This may be due to the interference task, which substantially increased error rates. Nevertheless, we found differences between the electrophysiological profiles linked with multiple vs. single sound presentation during sleep. Sigma spectral power predicted improvements in performance for the objects cued five times, but not for those cued once. For sounds presented once, benefits from sleep were predicted by post-sound power in the delta band. Although our results did not fully resolve the question of the relationship between the number of reactivation events and subsequent memory benefits, they inform future research using targeted memory reactivation to selectively bias memory during sleep.