Sex-Related Differences in the Effects of Sleep Habits on Verbal and Visuospatial Working Memory.

Seishu Nakagawa,Atsushi Sekiguchi,Takamitsu Shinada,Ryuta Kawashima,Ryoichi Yokoyama,Sugiko Hanawa,Yuka Kotozaki,Rui Nouchi,Yuki Yamamoto,Tsuyoshi Araki,Keiko Kunitoki,Kunio Iizuka,Yasuyuki Taki,Hikaru Takeuchi,Carlos M. Miyauchi,Yuko Sassa

doi:10.3389/fpsyg.2016.01128

Abstract

Poor sleep quality negatively affects memory performance, and working memory in particular. We investigated sleep habits related to sleep quality including sleep duration, daytime nap duration, nap frequency, and dream content recall frequency (DCRF). Declarative working memory can be subdivided into verbal working memory (VWM) and visuospatial working memory (VSWM). We hypothesized that sleep habits would have different effects on VWM and VSWM. To our knowledge, our study is the first to investigate differences between VWM and VSWM related to daytime nap duration, nap frequency, and DCRF. Furthermore, we tested the hypothesis that the effects of duration and frequency of daytime naps and DCRF on VWM and VSWM differed according to sex. We assessed 779 healthy right-handed individuals (434 males and 345 females; mean age: 20.7 ± 1.8 years) using a digit span forward and backward VWM task, a forward and backward VSWM task, and sleep habits scales. A correlation analysis was used to test the relationships between VWM capacity (VWMC) and VSWM capacity (VSWMC) scores and sleep duration, nap duration, nap frequency, and DCRF. Furthermore, multiple regression analyses were conducted to identify factors associated with VWMC and VSWMC scores and to identify sex-related differences. We found significant positive correlations between VSWMC and nap duration and DCRF, and between VWMC and sleep duration in all subjects. Furthermore, we found that working memory capacity (WMC) was positively correlated with nap duration in males and with sleep duration in females, and DCRF was positively correlated with VSWMC in females. Our finding of sex-related differences in the effects of sleep habits on WMC has not been reported previously. The associations between WMC and sleep habits differed according to sex because of differences in the underlying neural correlates of VWM and VSWM, and effectiveness of the sleep habits in males and females.

Highlights

Poor sleep quality has a negative affect on memory performance, working memory (Valdez et al, 2008)
The regression analysis revealed that nap duration and dream content recall frequency (DCRF) were significantly associated with VSWM Capacity (VSWMC) in all subjects, whereas sleep duration was significantly associated with VWM Capacity (VWMC)
Nap duration was significantly correlated with VWMC and VSWMC in males, whereas sleep duration was significantly correlated with VWMC and VSWMC in females

Summary

Introduction

Poor sleep quality has a negative affect on memory performance, working memory (Valdez et al, 2008). Considerable evidence suggests that sleep habits, such as sleep duration, daytime nap duration, nap frequency, and dream content recall, are related to the quality of sleep. Daytime naps increase alertness and cognitive performance (Milner and Cote, 2009) and, improve learning and memory. The duration and frequency of daytime naps have an impact on memory performance. Because one can memorize the contents of dreams, the act of recalling a dream must involve memory operations. Dream content recall may be enhanced by increasing the capacity of short-term memory and imaginal life (Martinetti, 1985). High dream content recall frequency (DCRF) is associated with higher visuospatial IQ (Butler and Watson, 1985) and absorption in imagery, according to the results of a subjective questionnaire (Schredl et al, 1997). Several studies have been unable to replicate these findings or have reported contradictory results (Dumel et al, 2015)

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