Napping between scylla and charybdis of N1 and N3: latency to N2 in a brief afternoon nap can be reduced by binaural beating

Abstract

ABSTRACT Afternoon nap is regarded as a potent behavioral strategy minimizing sleepiness and fatigue. The benefits of afternoon naps require the accumulation of, at least, 3 min of stage 2 sleep. However, there are practical disadvantages of nap longer than 10–15 min, such as greater length of time consumed by the nap, appearance of slow wave sleep causing greater sleep inertia right after the nap, and possible detrimental impact of such nap on subsequent nocturnal sleep. We previously found that a binaural beat treatment that is a dichotic presentation of two almost equivalent pure tones with slightly different frequencies led to a reduction of latency to stage 2 sleep. To replicate this result and to examine whether such reduction leads, in turn, to the earlier appearance of slow wave sleep, we asked 23 and 21 healthy volunteers to nap in the afternoon for 30 and 20 min, respectively. Almost half of volunteers showed latency to stage 2 longer than 17 min, but most of them responded to the treatment by its reduction. The following occurrence of slow wave sleep reduced level of alertness self-assessed right after the nap. We concluded that latency to stage 2 sleep might be experimentally challenged by binaural beating.