Sleep physiology predicts memory retention after reactivation

Both sleep and future relevance influence memory consolidation; however, limited research has investigated their role in memory reconsolidation. We manipulated the future relevance of both stable and labile memories in need of reconsolidation. Two groups learned two blocks of syllable pairs on one evening and were told they would be tested on one of the blocks later. On the second evening, one group (Labile) received reminders designed to return their memories of syllable pairs to a labile state, while a second group (Stable) received reminders designed to leave these memories in a stable state. No significant differences in memory retention were found between blocks or groups the following morning. Frontal delta (0.5-4 Hz) electroencephalographic power during Stage 2 sleep correlated positively with retention of future-relevant material exclusively in the Labile group. Central theta (4-8 Hz) electroencephalographic power during rapid eye movement (REM) sleep correlated positively with the extent to which the Labile group selectively retained future-relevant material. These relationships suggest that sleep-dependent processes are involved in an economical reprocessing of memories beyond the initial stages of consolidation.