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

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 (6.5h nocturnal sleep opportunity) or split sleep (5h nocturnal sleep +1.5h 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.