Effects of Daytime Sleep on the Consolidation of Declarative Memory in Humans

Abstract

The effects of daytime sleep consisting exclusively of non-REM (NREM) sleep on the consolidation of declarative memory and overall functional status were studied in humans. In addition, the effects of daytime sleep on memory were studied in relation to the level of fixation of assimilated information. At the beginning of each experiment, the subject was given a declarative memory task: to remember 60 semantically unrelated pairs of words, 30 of which were memorized once and 30 twice; at the end of the experiment, the level of memory fixation was assessed. Each subject took part in two experiments: a test protocol, in which training was followed by sleep, and a control protocol, in which a video was watched instead of sleeping. The results showed that daytime sleep facilitated the reproduction of declarative memory, with improvements in the remembering of the 30 pairs of words memorized once but not in remembering the 30 pairs of words memorized twice. The dynamics of a simple sensorimotor reaction and subjective assessments of wellbeing, activity, and mood with and without sleep were similar, and there were no significant differences between the two types of experiment.