Does splitting sleep improve long-term memory in chronically sleep deprived adolescents?

Abstract

Sleep aids the encoding and consolidation of declarative memories, but many adolescents do not obtain the recommended amount of sleep each night. After a normal night of sleep, there is abundant evidence that a daytime nap enhances the consolidation of material learned before sleep and also improves the encoding of new information upon waking. However, it remains unclear how learning is affected when sleep is split between nocturnal and daytime nap periods during a typical school week of restricted sleep. We compared long-term memory in 58 adolescents who underwent two simulated school weeks of suboptimal continuous (6.5 h nocturnal sleep opportunity) or split sleep (5 h nocturnal sleep +1.5 h daytime nap at 14:00). In the first week, participants encoded pictures in the late afternoon on Day 5 and were tested after 2-nights of recovery sleep. On 3 consecutive days in the second week, participants learned about six species of amphibians in the morning, and six different amphibians in the late afternoon. Testing was performed in the evening following a night of recovery sleep. In the first week, the split sleep group recognized more pictures. In the second week, they remembered more facts about species learned in the afternoon. Groups did not differ for species learned in the morning. This suggests that under conditions of sleep restriction, a split sleep schedule benefits learning after a nap opportunity without impairing morning learning, despite less preceding nocturnal sleep. While not replacing adequate nocturnal sleep, a split sleep schedule may be beneficial for chronically sleep restricted learners.

A daytime nap restores hippocampal function and improves declarative learning

“…Total or partial sleep restriction can compromise new memory formation [ 43–45 ] (although see [ 46 ]). A daytime nap has been shown to be beneficial—both in the context of sleep restriction [ 11 ], as well as following a normal night of sleep [ 10 ], reinforcing the idea that sleep may not just necessary for normative cognitive performance, but may also boost memory beyond that of habitual, nocturnal sleep [ 47 ]. In this study, we showed that participants who had a 90-minute afternoon nap in addition to a habitual, nonrestricted night of sleep encoded 21% more word pairs on average than those who stayed awake during the nap period.…”

“…We recently demonstrated that a mid-afternoon nap facilitates picture encoding [ 11 ] and found behavioral evidence that suggested enhanced hippocampal function as a plausible mechanism [ 12 ]. Memory encoding following sleep may occur as a result of (1) improvement in attentiveness to the learned material [ 13 ], (2) active systems consolidation, resulting from the transfer of labile memories in the hippocampus to neocortex for long-term storage, thus freeing up hippocampal encoding capacity for new learning [ 14 ], or (3) synaptic downscaling [ 15 ] whereby synaptic connections potentiated during wakefulness are downscaled to avoid saturation and to increase the signal-to-noise ratio for salient information.…”

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

“…Memory was tested after one night of recovery sleep on day R2 2 (20:30) via two-alternative forced choice questions followed by confidence ratings (certain, somewhat certain and guess). Consistent with prior work using this task (Cousins, et al, 2019b, 2019c, 2019d), our analysis focussed on certain responses that were corrected for response bias (correct-incorrect). We conducted a 2×2×2 mixed ANOVA to examine the effects of schedule (split/continuous), duration (6.5h/8h), and time (morning/afternoon) on certain memory (correct−incorrect).…”

“…Addressing this, the current study replicated our prior experiment with two additional groups of adolescents (Table 1) that were afforded the minimum recommended for this age group of 8h sleep opportunity each day (8h-split and 8h-continuous), then compared their performance with groups from the prior study (6.5h-split and 6.5h-continuous) (Cousins et al, 2019b). The effect of these schedules on sleep physiology and declarative memory (picture encoding and factual knowledge task) was investigated across two simulated school weeks (Fig.…”

“…To assess the impact of splitting sleep on learning, we recently examined performance during two typical school weeks of restricted sleep in adolescents (6.5h sleep opportunity each day), when sleep was either split between the night (5 h) and a daytime nap (1.5 h), or obtained nocturnally in one continuous sleep episode (Cousins et al, 2019b). We found that splitting sleep significantly improved declarative learning shortly after the nap in the afternoon.…”