Age- and Sex-Related Differences in N2 Sleep EEG Spectral Power: Implications for Thalamocortical Biomarker Development in ADHD

Sleep spindles, generated by thalamocortical circuits during NREM Stage 2 sleep, play a critical role in sensory gating and memory consolidation. Reduced spindle activity has been consistently observed in individuals with Attention Deficit Hyperactivity Disorder (ADHD), implicating thalamic inhibitory dysfunction in attentional dysregulation. However, normative trajectories of sleep spindle-band (sigma, 12-15 Hz) power across the adult lifespan remain incompletely characterized, limiting the utility of EEG spectral features as clinical biomarkers. Using the Sleep-EDF Expanded database (n=78 healthy adults, ages 25-101), we extracted EEG band power during N2 sleep and examined associations with age and sex. Sigma band power showed a significant negative correlation with age (R=-0.39, p<0.001), with a decline of 0.054 dB per year representing a cumulative loss of approximately 2.7 dB over 50 years. Multiple regression revealed that age and sex together explained 28.9% of variance in sigma power (R²=0.289, p<0.001). Females demonstrated significantly higher sigma power than males (2.3 dB, p<0.001), with sex-stratified analysis revealing that the age-related decline was primarily driven by males (R=-0.51, p=0.001) while females showed a non-significant trend (R=-0.30, p=0.054). These findings establish quantitative normative trajectories for sleep spindle-band activity across the adult lifespan and highlight sex as a critical covariate in EEG biomarker development. The convergence of age-related sigma power reduction with known spindle deficits in ADHD suggests that lifespan EEG trajectories may inform diagnostic thresholds and pharmacological targets for attentional dysregulation.