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WIREs Cogn Sci
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Sleep and cognition

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Abstract Sleep is a complex physiologic state, the importance of which has long been recognized. Lack of sleep is detrimental to humans and animals. Over the past decade, an important link between sleep and cognitive processing has been established. Sleep plays an important role in consolidation of different types of memory and contributes to insightful, inferential thinking. While the mechanism by which memories are processed in sleep remains unknown, several experimental models have been proposed. This article explores the link between sleep and cognition by reviewing (1) the effects of sleep deprivation on cognition, (2) the influence of sleep on consolidation of declarative and non‐declarative memory, and (3) some proposed models of how sleep facilitates memory consolidation in sleep. Copyright © 2010 John Wiley & Sons, Ltd. This article is categorized under: Psychology > Memory Neuroscience > Behavior

The human sleep cycle. Across the night, NREM and REM sleep cycle every 90 min in an ultradian manner, while the ratio of NREM to REM sleep shifts. During the first half of the night, NREM stage N3 (SWS) dominates, while N2 and REM sleep prevail in the latter half of the night. EEG patterns also differ significantly between sleep stages, with electrical oscillations such as K complexes and sleep spindles occurring during stage 2 NREM, slow (0.5–4 Hz) delta waves developing in SWS, and theta waves seen during REM.

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Sleep‐dependent development of insight. (a) Number reduction task: subjects were asked to determine the final digit in a series by processing digits from left to right according to two simple rules. However, subjects who gained insight into a hidden rule could determine the correct response after only the second digit presentation versus the sixth in those who did not gain insight. After initial training, subjects were retested after periods of wake or sleep—W/D: daytime wake; W/N: overnight sleep deprivation; S/N: nocturnal sleep. Subjects who slept had more than twice the chance of gaining insight compared to either of the wake groups. Adapted from [28]. (b) Inference pair performance: after initial training, subjects were tested after 12 h of daytime wake (red), 12 h including a night of sleep (green), or a full 24‐h day (blue). 1°: first order association (e.g., A = > C); 2°: second order association (e.g., A = < D). In the wake group (red), there was no difference in performance between first and second order associations. Both sleep groups (green and blue) performed significantly better on second order associations compared to first order associations. *p < 0.05. (Adapted with permission from Ref 29. Copyright 2007 Nature Publishing Group).

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The influence of sleep on emotional memory. Change in recognition rate of emotional or neutral images is demonstrated 12 h from initial encoding compared to 30 min after encoding. Left: neutral objects (striped bars) and their neutral backgrounds (solid bars) both show 6–11% deterioration across the 12 h interval, whether across a period of daytime wake or across a night with sleep; Right: the same pattern is seen for emotional objects (striped bars) and neutral backgrounds (solid bars), except that emotional objects are recognized significantly better after a night of sleep than either objects or backgrounds in any other condition.

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Sleep‐dependent enhancement of performance on declarative memory tasks. Two different memory tasks show sleep‐dependent improvements in performance. (a) Benefits of early and late night sleep on the paired associates list: performance improvement was significantly greater following early sleep (green bar left) compared to the early wake control (red bar left), and compared to late sleep (green bar right). There was no significant difference between the late sleep (green bar right) and late wake (red bar right) groups. *p < 0.05; **p < 0.01. Adapted from Ref [22]. (b) Paired associates task and effect of interference: there was a modest non‐significant improvement in performance after sleep (green bar left compared to wake (red bar left). Performance improved significantly after sleep for the group that underwent interference training (green bar right) compared to the interference wake group (red bar right) and significantly more so than in the no interference condition (left). (*) 0.05 ≤ p ≤ 0.10, *p < 0.05, ***p < 0.001. (Adapted with permission from Ref 25. Copyright 2006 MIT Press).

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Sleep‐dependent enhancement of performance on procedural memory task. Three different procedural tasks show sleep dependent improvements in performance. (a) Visual discrimination task: performance improvements were seen only in groups retested after a night of sleep (green circles), and not in groups retested after equivalent amounts of daytime wake (red circles). (Adapted with permission from Ref 14. Copyright 2000 MIT Press). (b) Finger‐tapping motor sequence task: performance improvements were seen only after a night of sleep (green bars). Left panel—subjects trained in the morning and retested that evening (PM) and again the next morning (AM); Center panel—the same as Left panel, except that subjects wore mittens across the initial period of daytime wakefulness to eliminate interference as a possible cause of the lack of PM improvement; Right panel—subjects trained in the evening and retested the following morning and again that evening show improvement at both post‐sleep tests. (Adapted with permission from Ref 17. Copyright 2002). (c) Motor adaptation to a virtual sideways force shows improved accuracy in direction of movement after sleep, but not after an equivalent period of daytime wake. (Adapted with permission from Ref 20. Copyright 2004 Nature Publishing Group).

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Neurobehavioral responses to varying doses of daily sleep. Three different neurobehavioral assays served to measure cognitive performance capability and subjective sleepiness. Each panel displays group averages for subjects in the 8 h (red lines), 6 h (green lines), and 4 h (lines) chronic sleep period conditions across 14 days, and in the 0 h (blue lines) sleep condition across 3 days. Upward corresponds to worse performance on the PVT (left), and to better performance on the DSST (center) and the SAST (right). The curves represent statistical non‐linear model‐based best‐fitting profiles of the response to sleep deprivation. The mean ± s.e.m. ranges of performance for 1 and 2 days of total sleep deprivation are shown as light and dark gray bands, respectively, allowing comparison with the 14‐day chronic sleep restriction conditions. For the DSST and SAST, these gray bands are curved parallel to the practice effect displayed by the subjects in the 8 h sleep period condition to compensate for different amounts of practice on these tasks. (Adapted with permission from Ref 3. Copyright 2003 Sleep Research Society).

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