Abstract Biological sex profoundly shapes brain function, yet its precise influence on neural oscillations was poorly understood. Despite decades of research, studies investigating sex-based variations in electroencephalographic (EEG) signals have yielded inconsistent findings that obstructs what may be a potentially crucial source of inter-individual variability in brain function. To address this, we analyzed five publicly available resting-state datasets, comprising EEG data (n=445) and iEEG data (n=103). Our results revealed striking age-dependent sex differences: older adults (30-80 years) exhibited robust sex differences, with males showing heightened low alpha (8-9 Hz) activity in temporal regions and attenuated low beta (16-20 Hz) oscillations in parietal-occipital areas compared to females. Intriguingly, these sex-specific patterns were absent in younger adults (20-30 years), suggesting a complex interplay between sex and aging in shaping brain dynamics. Furthermore, we identified consistent sex-related activity in the precentral gyrus with the results of scalp EEG, potentially driving the observed scalp EEG differences. This multi-level analysis allowed us to bridge the gap between cortical and scalp- level observations, providing a more comprehensive picture of sex-related neural dynamics. To further investigate the functional implications of these oscillatory differences, we conducted correlation analyses to uncover significant associations between sex-specific oscillatory patterns and several lifestyle factors (behavioral and anthropometric measures) in older adults. This comprehensive investigation demonstrates the complex interplay between sex, age, and neural oscillations, revealing the variability in brain dynamics. And our findings highlight the importance of careful demographic consideration in EEG research design to ensure fairness in capturing the full spectrum of neurophysiological diversity. Significance statement The influence of biological sex and age on neural oscillations had been a long- standing, unresolved question in EEG research, largely unaddressed due to limited sample sizes and simplistic demographic matching. Our study leverages large-scale, open datasets to tackle this issue, analyzing hundreds of participants across five datasets. Our findings demonstrate substantial sex- based differences in even resting-state EEG baselines, particularly in low alpha and low beta bands, uncovering a significant source of variability in neural activity. By connecting these sex and age-related variations to potential neural circuit mechanisms and lifestyle factors, our findings highlight the importance of careful demographic consideration in EEG research design in EEG experimental design to accurately capture the rich spectrum of neurophysiological variability across the lifespan.

Aging amplifies sex differences in low alpha and low beta EEG oscillations