Daytime naps improve procedural motor memory

Background and purpose: To investigate the impact of a short daytime nap on procedural and declarative memory consolidation. Patients and methods: Following a normal night's sleep, 34 young healthy subjects were randomly assigned to a nap or wake condition of about 45 min in the early afternoon after learning procedural and declarative memory tasks. Subjects were controlled for alertness and cortisol secretion. Results: The afternoon naps were dominated by sleep stage 2 but contained some slow wave sleep (SWS) and rapid eye movement (REM) sleep as well. Naps significantly improved procedural, but not declarative, memory. Females showed more improvement than males in the declarative memory tasks irrespective of nap or wake. There was no difference between groups with respect to cortisol secretion or alertness. Conclusions: A short nap is favorable for consolidation of procedural memory. The possibly confounding effect of gender should always be considered in research on sleep and memory.