Circadian and homeostatic processes influence daytime nap architecture

Abstract

Introduction Besides being a useful tool for coping with sleep deprivation, naps can reduce sleepiness and improve cognitive performance. However, few studies so far have examined what factors regulate its structure. Therefore, we aimed to investigate if circadian preference influences daytime nap architecture. Materials and methods Following a week of actigraphy monitoring of the sleep/wake cycle, a total of 43 healthy young adults (19 females, 22.16 ( ± 3.82) years) filled out the Morningness–Eveningness Questionnaire (MEQ) and took a 90 min polysomnography-recorded nap. MEQ score, nocturnal sleep data and minutes of prior wakefulness were correlated with nap sleep variables. Results There is a negative correlation between MEQ Score (47.93 ( ± 10.93)) and Slow Wave Sleep% (SWS) (r = −.364, p = .044) and a positive correlation with Stage N1% (r = .371, p = .014), meaning that morning preference is associated with increased SWS and decreased N1 in a daytime nap. No correlations were found between MEQ Score and total sleep time (nap or nocturnal, for either the previous night or the mean 5 previous nights), Stage N2%, or REM%. The mean 5 previous nights bedtime (r = −.381, p = .038) and wake time (r9 = −.362, p = .049) were also negatively correlated with SWS, whereas the previous night bedtime (r = .375, p = .013) and wake time (r = .302, p = .049) were positively correlated with N1, that is, going to bed and waking up earlier predicted greater SWS% and smaller N1%, supporting MEQ Score correlations. To rule out homeostatic sleep drive as an explanation for increased nap SWS in individuals with a morning preference, minutes of prior wakefulness were correlated with nap sleep data. No association was found between homeostatic sleep drive and SWS (r = 0,244, p > 0.05). However, increasingly amounts of N1 were associated with less time between waking and napping (r = −0.370, p = 0.015). Conclusion Morningness is associated with increased SWS in a daytime nap and prior wakefulness predicts time spent in N1, in healthy young adults. It is possible that this is because the scheduled nap timing was more suitable for individuals with a morning preference. Both components (circadian and homeostatic) should be taken into account when prescribing naps to ensure maximal restorative effects. Acknowledgements Supported by grants from CAPES and CNPq. We would like to thank all the subjects that volunteered for this study.