Measuring Neural Mechanisms Underlying Sleep-Dependent Memory Consolidation During Naps in Early Childhood

Abstract

Sleep is critical for daily functioning. One important function of sleep is the consolidation of memories, a process that makes them stronger and less vulnerable to interference. The neural mechanisms underlying the benefit of sleep for memory can be investigated using polysomnography (PSG). PSG is a combination of physiological recordings including signals from the brain (EEG), eyes (EOG), and muscles (EMG) that are used to classify sleep stages. In this protocol, we describe how PSG can be used in conjunction with behavioral memory assessments, actigraphy, and parent-report to examine sleep-dependent memory consolidation. The focus of this protocol is on early childhood, a period of significance as children transition from biphasic sleep (consisting of a nap and overnight sleep) to monophasic sleep (overnight sleep only). The effects of sleep on memory performance are measured using a visuospatial memory assessment across periods of sleep and wakeful-rest. A combination of actigraphy and parent report is used to assess sleep rhythms (i.e., characterizing children as habitual or non-habitual nappers). Finally, PSG is used to characterize sleep stages and qualities of those stages (such as frequencies and the presence of spindles) during naps. The advantage of using PSG is that it is the only tool currently available to assess sleep quality and sleep architecture, pointing to the relevant brain state that supports memory consolidation. The main limitations of PSG are the length of time it takes to prepare the recording montage and that recordings are typically taken over one sleep bought. These limitations can be overcome by engaging young participants in distracting tasks during application and combining PSG with actigraphy and self/parent-report measures to characterize sleep cycles. Together, this unique combination of methods allows for investigations into how naps support learning in preschool children.

Figure 1:

Example electrode placement and description of activity recorded via PSG.

Figure 2:

Overview of protocol. Each square represents one day.

Figure 3:

Examples of screen displays during the visuospatial memory task.

Figure 4:. Recall accuracy on the visuospatial memory task was tested immediately following encoding (“Immediate”), following the nap opportunity (“Delayed”), and again the following day (“24-hour”) across two conditions: a nap-promoted condition (gray bars) and wake-promoted condition (white bars).

Error bars represent ± 1 SE. This figure is reprinted with permission from Kurdziel et al..

Figure 5:. Change in recall accuracy (delayed recall minus immediate recall) across the nap (gray bars) and wake (white bars) intervals for habitual nappers (who took five to seven naps per week) and non-habitual nappers (those who took zero to two naps per week).

Error bars represent ± 1 SE. This figure is reprinted with permission from Kurdziel et al..

Figure 6:. Sleep spindle density (spindles per minute of non-REM stage 2 sleep) associations with (A) immediate recall accuracy and (B) the change in recall accuracy from the immediate to delayed recall phase.

This figure is reprinted with permission from Kurdziel et al..