Cued memory reactivation during slow-wave sleep promotes explicit knowledge of a motor sequence

Cousins, J. , Lewis, P. , El-Deredy, W. , Parkes, L. & Hennies, N.

University of Manchester

Memories are gradually consolidated after initial encoding, and this can sometimes lead to the emergence of explicit knowledge from what was initially implicit learning. The exact processes underlying this reorganization remain unclear. Here, we used a serial reaction time task (SRTT) to determine whether targeted memory reactivation (TMR) of specific memory traces during slow-wave sleep promotes the emergence of explicit knowledge. Participants learned two procedural 12-item sequences (A and B) that differed in cue order and in the set of four associated tones (higher or lower pitch). Subsequent overnight sleep was monitored, and the tones associated with one learned sequence were replayed during slow-wave sleep. Upon waking, participants demonstrated greater explicit knowledge (P=0.005) as well as improved procedural skill (P=0.04) for the cued sequence relative to the un-cued sequence. Furthermore, frontal slow oscillations (~1Hz) during TMR predicted explicit knowledge (r=0.7, P=0.01), while fast spindles (13.5-15Hz) over right motor regions involved in task learning predicted procedural skill enhancement (r=0.71, P=0.01). These findings show that targeted memory reactivation during sleep can alter memory representations to promote the extraction of explicit knowledge, suggesting that reactivation during sleep is a key mechanism for actively restructuring memory traces.