Long-term reliability and stability of parameterized resting state EEG: Evidence from a five-year follow-up

Several aspects of parameterised neural activity, including the aperiodic exponent and individual peak alpha frequency, have emerged as promising biomarkers for ageing, pathology, and cognitive decline. Their potential clinical application is tempered by a lack of evidence on long-term temporal stability. Existing investigations have largely relied on cross-sectional designs or considered stability for up to 90 days. Here, we examined five-year reliability, stability, and age-related changes in periodic and aperiodic neural activity using electroencephalography in adults aged 20-70 years. Resting-state EEG was recorded in two sessions, approximately five years apart. We extracted the aperiodic exponent, aperiodic offset, peak alpha power, and individual alpha peak frequency from each channel and examined test-retest reliability at both the channel and cluster levels. All parameters demonstrated fair to excellent test-retest reliability (intraclass correlations = 0.51-0.88). Linear mixed models revealed that individual peak alpha frequency decreased, the aperiodic exponent flattened, and parameterized alpha power remained unchanged. There were no interactions between time and age. Our findings suggest that parameterized activity is reliable over long timeframes and likely captures neural ageing. Spectral parameterization may provide a means of characterizing gradual, normative neurophysiological ageing. Future research should explore the utility of identifying deviations that may indicate pathology.