Abstract
This meta-analysis examines EEG sleep spindle and macrostructure differences in humans related to healthy aging, sex, and cognitive ability. Inclusion criteria required quantitative EEG data of healthy subjects, including sleep spindle properties and sleep polysomnography comparing younger to older subjects, females to males, and/or correlations with cognitive ability scores. The search included seven databases. The Mixed Methods Appraisal Tool (MMAT) calculated the study quality (risk of bias). Two meta-analyses used Hedges' g, and one averaged correlation (95% CI), all conducted with Meta-Essentials v1.4, with standard assessments of heterogeneity, publication bias, and meta-regression, supplemented by subgroup and sensitivity analyses. Results provide tables, forest plots, funnel plots, and bubble plots. k = 42 studies with N = 1,878 healthy subjects met our criteria. With age, sleep spindles decreased in amplitude, density, and duration. Sleep quality was reduced in older subjects showing shorter durations of both slow wave sleep (SWS) and rapid-eye movement (REM) sleep. Females revealed higher sleep spindle power (11-16 Hz), more prominent in older subjects; greater sleep efficiency, more total sleep time (TST), and longer SWS. Correlations between sleep properties and cognitive ability revealed age-dependent effects. Results yield key considerations in population comparisons and when targeting spindle activity, both for mechanistic research and for neuropsychiatric treatment. Yet further systematic investigations are warranted.