Abstract
Sleep enhances memory consolidation. Bearing in mind that food intake produces many metabolic signals that can influence memory processing in humans (e.g., insulin), the present study addressed the question as to whether the enhancing effect of sleep on memory consolidation is affected by the amount of energy consumed during the preceding daytime. Compared to sleep, nocturnal wakefulness has been shown to impair memory consolidation in humans. Thus, a second question was to examine whether the impaired memory consolidation associated with sleep deprivation (SD) could be compensated by increased daytime energy consumption. To these aims, 14 healthy normal-weight men learned a finger tapping sequence (procedural memory) and a list of semantically associated word pairs (declarative memory). After the learning period, standardized meals were administered, equaling either ∼50% or ∼150% of the estimated daily energy expenditure. In the morning, after sleep or wakefulness, memory consolidation was tested. Plasma glucose was measured both before learning and retrieval. Polysomnographic sleep recordings were performed by electroencephalography (EEG). Independent of energy intake, subjects recalled significantly more word pairs after sleep than they did after SD. When subjects stayed awake and received an energy oversupply, the number of correctly recalled finger sequences was equal to those seen after sleep. Plasma glucose did not differ among conditions, and sleep time in the sleep conditions was not influenced by the energy intake interventions. These data indicate that the daytime energy intake level affects neither sleep’s capacity to boost the consolidation of declarative and procedural memories, nor sleep’s quality. However, high energy intake was followed by an improved procedural but not declarative memory consolidation under conditions of SD. This suggests that the formation of procedural memory is not only triggered by sleep but is also sensitive to the fluctuations in the energy state of the body.
Highlights
Previous studies have shown that human sleep enhances the conversion of labile, recently acquired information into stable, long-term memories, which means that volunteers showed greater savings for memory when sleeping versus nocturnal wakefulness after the learning process [1,2,3,4,5]
Memory Consolidation The results of the repeated-measures analyses of variance (ANOVA) are given in table 2
Time spent awake, stage 1 sleep, stage 2 sleep, stage 3 sleep, stage 4 sleep, rapid eye movement (REM) sleep, and movement arousal are given in minutes, and latency of the first period of slow-wave-sleep (SWS) and REM sleep are shown
Summary
Previous studies have shown that human sleep enhances the conversion of labile, recently acquired information into stable, long-term memories, which means that volunteers showed greater savings for memory when sleeping versus nocturnal wakefulness after the learning process [1,2,3,4,5] Such consolidation effects of sleep have been found for declarative and for procedural types of memory tasks. The question of whether the impairing effect of sleep loss on memory consolidation can be reversed by oversupplying energy has yet to be addressed Against this background, in the present study memory consolidation was tested in healthy male subjects participating in four conditions. In each sleep condition [i.e. sleep and total sleep deprivation (TDS), respectively] they once received an undersupply of energy, and once an oversupply of energy on the preceding day
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