Splitting sleep between the night and a daytime nap reduces homeostatic sleep pressure and enhances long-term memory

Abstract

Daytime naps have been linked with enhanced memory encoding and consolidation. It remains unclear how a daily napping schedule impacts learning throughout the day, and whether these effects are the same for well-rested and sleep restricted individuals. We compared memory in 112 adolescents who underwent two simulated school weeks containing 8 or 6.5 h sleep opportunities each day. Sleep episodes were nocturnal or split between nocturnal sleep and a 90-min afternoon nap, creating four experimental groups: 8 h-continuous, 8 h-split, 6.5 h-continuous and 6.5 h-split. Declarative memory was assessed with picture encoding and an educationally realistic factual knowledge task. Splitting sleep significantly enhanced afternoon picture encoding and factual knowledge under both 6.5 h and 8 h durations. Splitting sleep also significantly reduced slow-wave energy during nocturnal sleep, suggesting lower homeostatic sleep pressure during the day. There was no negative impact of the split sleep schedule on morning performance, despite a reduction in nocturnal sleep. These findings suggest that naps could be incorporated into a daily sleep schedule that provides sufficient sleep and benefits learning.

A sleep schedule incorporating naps benefits the transformation of hierarchical knowledge

“…Our findings extend previously reported benefits of naps for fact-learning in educational settings [ 15 ] to schema-based learning. The higher schema adaptability in the Nap group have been the result of stronger consolidation of recently acquired knowledge structures following napping.…”

“…In contrast to the findings related to fast spindles, we found no direct association between the amount of SWS, measured either via duration or amplitude, on memory performance. However, SWS could still benefit learning by providing an additional opportunity to relieve sleep pressure [ 15 ]. Such relief of homeostatic sleep pressure is theorized to help restore learning capacity, benefiting performance in the Nap group.…”

“…Moreover, adolescents restricted to as little as 5 h of sleep opportunity a night did not show inferior declarative memory consolidation for words compared to those with a 9-h sleep opportunity [ 57 ]. This suggests that consolidation may be unhindered provided a minimum amount of nocturnal SWS is obtained [ 15 , 58 ].…”

“…Recent research conducted in adolescents suggests that mid-afternoon naps which boost attention are beneficial in sleep schedules where nocturnal sleep is suboptimal in duration [ 14 ]. Such naps also benefit the learning of organized facts that engage long term memory [ 15 ]. However, it remains an open question whether the benefits of naps extend to the integration of altered and expanded knowledge based on previously constructed schemas, and how this may take place over recurrent nap opportunities.…”

Hypoxia Differentially Affects Healthy Men and Women During a Daytime Nap With a Dose-Response Relationship: a Randomized, Cross-Over Pilot Study

“…This apparent undisturbed sleep could be because the dose of sleep restriction was small and the exposure to hypoxia was short. In addition, similar protocols (such as the splitting sleep protocol) have even found positive effects from their implementation ( Cousins et al, 2021 ).…”