Topographic gradients of resting-state EEG alpha asymmetry: Network-specific lateralization and age-related dedifferentiation in healthy adults.

BACKGROUND: Alpha asymmetry, which quantifies hemispheric differences in alpha power (8-13 Hz), serves as a neurophysiological marker of cortical activation. While frontal alpha asymmetry has been extensively studied in affective disorders, full topographic characterization in healthy adults remains limited. METHODS: Resting-state EEG (eyes-closed) was recorded from 160 healthy adults (76 females, 84 males; age 18-49 years, M = 26.71, SD = 6.04) using the International 10-20 system. Alpha asymmetry indices were computed for eight electrode pairs spanning prefrontal, frontal, central, parietal, temporal, and occipital regions. Linear mixed-effects models were used to analyse the scalp distribution, age-related effects, and sex differences. RESULTS: A strong anterior-posterior gradient was observed, with minimal prefrontal asymmetry (Fp1/Fp2: estimated marginal mean = 0.58) increasing to maximal leftward dominance in central-parietal (C3/C4: estimated marginal mean = 1.35; P3/P4: estimated marginal mean = 1.35), and posterior temporal sites (T5/T6: estimated marginal mean = 1.42), F(7, 1120) = 449.61, p < .001, partial ηp2 = 0.74. Age negatively predicted asymmetry magnitude (β = -0.003, p = .028). No significant sex differences were found (F(1, 160) = 0.09, p = .771). After false discovery correction, we found that the subtle regional effects at parietal and posterior temporal sites did not reach statistical significance. CONCLUSIONS: Alpha asymmetry at rest exhibited a clear spatial pattern, corresponding to the architecture of sensory-motor and posterior language networks. We observed that the age-related reduction in alpha asymmetry is detectable earlier than previously expected. Although biological sex did not significantly influence hemispheric lateralization during youth to middle adulthood, subtle region-specific patterns warrant further theoretical investigation.