Abstract
The low-frequency high-amplitude oscillations of slow-wave sleep (SWS) are considered to promote the consolidation of episodic memory. Previous research suggests that sleep slow waves can be entrained and enhanced by presenting short acoustic stimuli to the up-states of endogenous waves. Several studies have investigated the effects of these increases in slow-wave activity on overnight memory consolidation, with inconsistent results. The aim of this meta-analysis was to evaluate the accumulated evidence connecting acoustic stimulation during sleep to episodic memory consolidation. A systematic literature search was conducted in October 2020 using PubMed, Web of Science, and PsycInfo. The main study inclusion criteria were the application of acoustic slow wave enhancement in healthy participants and an assessment of pre- and post-sleep episodic memory performance. Effect sizes were pooled using a random-effects model. A total of 10 primary studies with 11 experiments and 177 participants were included. Results showed a combined effect size (Hedges' g) of 0.25 (p = 0.07). Subgroup models based on young adults (n = 8), phase-locked stimulation approaches (n = 8), and their combination (n = 6) showed combined effect sizes of 0.31 (p = 0.051), 0.36 (p = 0.047), and 0.44 (p = 0.01), respectively. There was no indication of publication bias or bias in individual studies. Acoustic enhancement of SWS tends to increase the overnight consolidation of episodic memory but effects remain small and-with the exception of subgroup models-at trend levels. Currently, the evidence is not sufficient to recommend the use of commercially available devices.
Highlights
Recalling a memory, e.g. a new acquaintance’s name, might prove difficult in the evening after a long day
The aim of this meta-analysis was to evaluate the accumulated evidence connecting ip acoustic stimulation during sleep to episodic memory consolidation. r Methods: A systematic literature search was conducted in October 2020 using Pubmed, sc Web of Science and PsycInfo
Ript Methods sc Protocol registration nu This meta-analysis has been registered with the ResearchRegistry under the unique identifying a number researchregistry1004. d M Search strategy te The literature search was conducted with the following search term: Sleep AND AND AND memory
Summary
E.g. a new acquaintance’s name, might prove difficult in the evening after a long day. As the main differences in the study designs were based on the variables ‘type of sleep’ (nighttime or nap), ‘memory task’ (non-related stimuli or related d stimuli), ‘AS approach’ (PLAS or NPLAS) and ‘age’ (young or middle aged/old), subgroup analyses te were performed This allowed for a subgroup comparison of effect sizes as well as an p assessment of how much the differences in these variables contribute to the sample’s heterogeneity. As synchronization of stimulation to endogenous slow waves has been suggested to be essential [51], a fourth model was calculated including only studies that used a phase-locked stimulation approach rather than a non-phase-locked approach These 8 experiments used a PLAS algorithm where the stimulation is timed by the endogenous SO activity in a phase-specific manner t (see table 1). Even for the models that found the largest c effect sizes (model 5 and model 6), an n of 62 or 42, respectively, would be needed in order to Aachieve the same effect size with a statistical power of 80%
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