Slow waves during 20-minute naps and the consolidation of declarative memory

Sleep supports declarative memory consolidation, a benefit largely attributed to slow-wave sleep (SWS). Short 20-min naps contain little SWS and are dominated by stage N2, yet their effect on long-term retention is poorly characterised. Thirty-one healthy adults learned five nonsense syllable pairs embedded in a multimodal context (10 training trials with feedback). Sixteen took a polysomnographically recording of a 20-min afternoon nap; fifteen stayed awake for an equivalent interval performing a distracting task. Memory was tested on Day 1 and Day 7. The nap group showed less memory decay than the wake group (Welch t-test, p=0.044, d=0.77). Only four nappers reached stage N3. None of 14 prespecified sleep predictors, spanning spectral power, slow-wave morphology, spindle density and slow-wave-spindle coupling, was associated with memory change. Therefore, a brief nap predominantly characterized by N2, was associated with reduced forgetting across seven days, without identifiable oscillatory correlates