Rapid-Eye-Movement-Sleep (REM) Associated Enhancement of Working Memory Performance after a Daytime Nap

Abstract

The main objective was to study the impact of a daytime sleep opportunity on working memory and the mechanism behind such impact. This study adopted an experimental design in a sleep research laboratory. Eighty healthy college students (Age:17-23, 36 males) were randomized to either have a polysomnography-monitored daytime sleep opportunity (Nap-group, n=40) or stay awake (Wake-group, n=40) between the two assessment sessions. All participants completed a sleep diary and wore an actigraph-watch for 5 days before and one day after the assessment sessions. They completed the state-measurement of sleepiness and affect, in addition to a psychomotor vigilance test and a working memory task before and after the nap/wake sessions. The two groups did not differ in their sleep characteristics prior to and after the lab visit. The Nap-group had higher accuracy on the working memory task, fewer lapses on the psychomotor vigilance test and lower state-sleepiness than the Wake-group. Within the Nap-group, working memory accuracy was positively correlated with duration of rapid eye movement sleep (REM) and total sleep time during the nap. Our findings suggested that “sleep gain” during a daytime sleep opportunity had significant positive impact on working memory performance, without affecting subsequent nighttime sleep in young adult, and such impact was associated with the duration of REM. While REM abnormality has long been noted in pathological conditions (e.g. depression), which are also presented with cognitive dysfunctions (e.g. working memory deficits), this was the first evidence showing working memory enhancement associated with REM in daytime napping in college students, who likely had habitual short sleep duration but were otherwise generally healthy.

A daytime nap enhances visual working memory performance and alters event-related delay activity

“…(c) Average amplitude of occipital delay activity (ODA) by levels of load and nap condition spatial N-back task (Lau et al, 2015). Although an overall benefit of the nap to WM performance was observed by Lau et al (2015), block-by-block analyses showed that the nap only had significant benefits in the second and third blocks of the task and not the first. This pattern of results may reflect progressive decreases in attentional control in the wake conditions.…”

“…Thus, markers of sleep pressure such as SWS and NREM delta (0.5-4 Hz) power (Dijk, Brunner, Beersma, & Borbély, 1990) may predict sleep-related WM improvements. Given the results of Lau et al (2015), TST and REM sleep duration were predicted to be associated with post-nap WM improvements. Because WM has been associated with fluid intelligence (Engle & Kane, 1999), and fluid intelligence has been associated with sleep spindle activity (Bódizs et al, 2005;Fang et al, 2017;Schabus et al, 2006), sleep spindle density in NREM sleep was predicted to relate to WM performance or specifically sleep-related improvements in WM performance if sleep spindles have an active role in maintaining cognitive performance.…”

“…In a recent study, Lau, Wong, Lau, Hui, and Tseng (2015) investigated WM performance before and after a 90-min nap in comparison with a no-nap group. Lau et al utilized an Nback WM task that required participants to recall the location of a symbol that appeared two trials prior in one of 12 possible locations.…”

“…The delayedestimation task used asked participants to view two, four, or six uniquely colored squares, hold them in WM over a brief delay, and then, from memory, report the color of a probed square on a 360°color wheel. Data were analyzed at a trialby-trial level with mixed-effect modelling to capture performance changes over the task, an important consideration given the time-on-task effect (i.e., the progressive worsening of performance over time on tasks requiring sustained focus), its relationship to sleep and sleep loss (Lim & Dinges, 2008), and the potential for relationships between sleep and performance to vary over the duration of a task (Lau et al, 2015). Models were constructed to estimate the effect of the experimental conditions on two measures of WM performance, namely the odds of WM success and the error within success.…”

A Twenty-Minute Nap Boosts the Planning Domain of Executive Function in Sleep Deprived Late Adolescents

“…Our first interest was the optimal nap time, which has been controversial in many different studies, ranging from less than 10 min to 2 h. [12][13][14][15] Secondly, we were intrigued by the fact that executive function could be assessed using various computer games. 16 We decided to study the optimal nap duration among sleep deprived, otherwise healthy Korean late adolescents and the effect of a nap on their planning domain of executive function by comparing their performance before and after a nap using an easily accessible iPad game.…”