Sleep does not help relearning declarative memories in older adults

How sleep affects memory in older adults is a critical topic, since age significantly impacts both sleep and memory. For declarative memory, previous research reports contradictory results, with some studies showing sleep-dependent memory consolidation and some other not. We hypothesize that this discrepancy may be due to the use of recall as the memory measure, a demanding task for older adults. The present paper focuses on the effect of sleep on relearning, a measure that proved useful to reveal subtle, implicit memory effects. Previous research in young adults showed that sleeping after learning was more beneficial to relearning the same Swahili-French word pairs 12 hours later, compared with the same interval spent awake. In particular, those words that could not be recalled were relearned faster when participants previously slept. The effect of sleep was also beneficial for retention after a one-week and a 6-month delay. The present study used the same experimental design in older adults aged 71 on average but showed no significant effect of sleep on consolidation, on relearning, or on long-term retention. Thus, even when using relearning speed as the memory measure, the consolidating effect of sleep in older adults was not demonstrated, in alignment with some previous findings.