A daytime nap does not hamper sleep at night; instead it boosts a person's declarative memory performance. A nap has a beneficial effect on performance across multiple tasks, particularly for people who learned the material more strongly before sleep.
In contrast, a nap does not have the same enhancing effect in people who learned poorly prior to sleep, BBC radio reported.
Researchers in America tested how a 45-minute daytime nap, compared with no nap, influenced how well 11 male and 22 female undergraduate students were able to memorise factual and spatial information. The students, all caffeine, alcohol, and medication-free, were aged 23 years on average when they attended a sleep laboratory at the beginning of the study.
The students performed three tasks that required memorisation. One involved linking 60 unrelated word pairs, such as tree-nose; another required manoeuvring through a computerised maze and the last gave students five minutes to copy a complex figure. The students were randomly assigned individual sleep chambers where 16 napped and 17 rested quietly. After about 10 minutes, the no-nap group went to a separate room to watch television while the nappers completed their 45-minute sleep.
Two hours later, after all the students watched the same movie, the students were asked to recall word pairs, in which their speed and accuracy in the computerised maze were measured, and their ability to redraw the complex figure from memory was scrutinised.
Among the students deemed high performers in the initial tests, those who napped performed better than non-nappers on all three tasks at the re-test. By contrast, naps did not enhance the memory of those students who did not perform well initially.
The findings suggest that sleep, even in the form of a short daytime nap, help the brain selectively process well-learned information. The next step would be to look at the factors that produce enhanced learning and how these factors are associated with memory enhancement during sleep.