Sleep spectral power correlates of prospective memory maintenance

Abstract

Prospective memory involves setting an intention to act that is maintained over time and executed when appropriate. Slow wave sleep (SWS) has been implicated in maintaining prospective memories, although which SWS oscillations most benefit this memory type remains unclear. Here, we investigated SWS spectral power correlates of prospective memory. Healthy young adult participants completed three ongoing tasks in the morning or evening. They were then given the prospective memory instruction to remember to press "Q" when viewing the words "horse" or "table" when repeating the ongoing task after a 12-h delay including overnight, polysomnographically recorded sleep or continued daytime wakefulness. Spectral power analysis was performed on recorded sleep EEG. Two additional groups were tested in the morning or evening only, serving as time-of-day controls. Participants who slept demonstrated superior prospective memory compared with those who remained awake, an effect not attributable to time-of-day of testing. Contrary to prior work, prospective memory was negatively associated with SWS. Furthermore, significant increases in spectral power in the delta-theta frequency range (1.56 Hz-6.84 Hz) during SWS was observed in participants who failed to execute the prospective memory instructions. Although sleep benefits prospective memory maintenance, this benefit may be compromised if SWS is enriched with delta-theta activity.

Figure 1.

Schematic of study timeline for each experimental condition.

Figure 2.

Behavioral data. Proportion of successful prospective memory intention executions (i.e., the number of times the participant successfully responded to the prospective memory prompt divided by the total number of prospective memory prompts) in each condition. Error bars indicate the standard error. (*) P < 0.05, (ns) nonsignificant.

Figure 3.

Spectral power analysis. (A) Hypnogram (top) and full night spectrogram (bottom) at electrode C4 of a single participant who did successfully remember the prospective memory intention (left) and a single participant who did not successfully remember the prospective memory intention (right). (B) Group-level SWS power spectrum (averaged power across frontal and central electrodes). Power spectral density (PSD) was normalized within each participant by dividing power at each frequency bin by the average PSD in the 0–20 Hz range. The gray box highlights frequencies in which there were significant differences between participants who remembered the prospective memory intention (solid purple line) and participants who did not remember the prospective memory intention (dashed orange line). Cluster statistic displayed above plot. Shaded areas indicate the standard error. (C) PSD averaged across frequencies in the significant cluster (B) for successful and unsuccessful participants. Error bars indicate the standard error.