Topographic gradients of resting-state EEG alpha asymmetry: Network-specific lateralization and age-related dedifferentiation in healthy adults.
Caravaglios G, Caravaglios L, et al. • International journal of psychophysiology : official journal of the International Organization of Psychophysiology • 2026
Alpha asymmetry at rest exhibited a clear spatial pattern corresponding to the architecture of sensory-motor and posterior language networks, with an anterior-posterior gradient, age-related reduction in asymmetry magnitude detectable earlier than previously expected, and no significant sex differences.
Key Findings
Results
A strong anterior-posterior gradient in alpha asymmetry was observed, with minimal prefrontal asymmetry increasing to maximal leftward dominance at central-parietal and posterior temporal sites.
Prefrontal asymmetry (Fp1/Fp2) had an estimated marginal mean of 0.58, representing the lowest asymmetry value.
Central-parietal sites (C3/C4 and P3/P4) both showed estimated marginal means of 1.35.
Posterior temporal sites (T5/T6) showed the highest asymmetry with an estimated marginal mean of 1.42.
The overall effect of electrode site was highly significant: F(7, 1120) = 449.61, p < .001, partial ηp² = 0.74.
The spatial pattern was interpreted as corresponding to the architecture of sensory-motor and posterior language networks.
Results
Age negatively predicted alpha asymmetry magnitude, with age-related reduction in asymmetry detectable earlier than previously expected.
Age was a significant negative predictor of asymmetry magnitude: β = -0.003, p = .028.
The sample spanned ages 18–49 years (M = 26.71, SD = 6.04), indicating this reduction was observed in a relatively young adult population.
The authors characterize this as an age-related dedifferentiation that is detectable earlier than previously expected.
The finding is framed in the context of broader age-related changes in hemispheric lateralization across healthy adulthood.
Results
No significant sex differences in alpha asymmetry were found across the scalp in healthy adults aged 18–49 years.
The sex effect was non-significant: F(1, 160) = 0.09, p = .771.
The sample included 76 females and 84 males.
The authors note that subtle region-specific patterns warrant further theoretical investigation despite the overall null finding.
The null sex finding applied across all eight electrode pairs spanning prefrontal, frontal, central, parietal, temporal, and occipital regions.
Results
After false discovery rate correction, subtle regional effects at parietal and posterior temporal sites did not reach statistical significance.
Parietal (P3/P4) and posterior temporal (T5/T6) sites showed effects that were apparent before correction but failed to survive false discovery rate correction.
This correction was applied to control for multiple comparisons across the eight electrode pairs.
Despite this, the overall anterior-posterior gradient remained highly significant.
Methods
The study characterized full topographic alpha asymmetry in healthy adults using linear mixed-effects models across eight electrode pairs spanning multiple scalp regions.
160 healthy adults were recorded using resting-state EEG (eyes-closed) with the International 10-20 system.
Alpha asymmetry indices (8–13 Hz) were computed for eight electrode pairs: prefrontal (Fp1/Fp2), frontal (F3/F4, F7/F8), central (C3/C4), parietal (P3/P4), temporal (T3/T4, T5/T6), and occipital (O1/O2).
Linear mixed-effects models were used to analyze scalp distribution, age-related effects, and sex differences.
The study specifically aimed to address the limited topographic characterization of alpha asymmetry in healthy adults, beyond the frontal region typically studied in affective disorders.
What This Means
This research suggests that the brain's left and right hemispheres differ systematically in their resting electrical activity (alpha brainwaves, 8–13 Hz), and that this difference varies in a clear pattern from front to back across the scalp. In 160 healthy adults, the researchers found that regions near the front of the head (prefrontal areas) showed very little difference between the two hemispheres, while regions in the middle and toward the back of the head — particularly areas linked to motor control and language — showed much stronger left-side dominance. This spatial pattern maps onto known brain networks for sensory-motor processing and language, suggesting that these resting-state asymmetries reflect meaningful differences in how the two hemispheres are organized.
The study also found that as people get older — even within the relatively young age range of 18 to 49 — this hemispheric difference tends to gradually decrease. This process, sometimes called 'dedifferentiation,' means the two hemispheres become slightly more similar in their activity levels with age. Importantly, the researchers found this decline starting earlier in adulthood than prior research had suggested. On the other hand, being male or female did not meaningfully influence how asymmetric the brain's alpha activity was at rest.
These findings matter because alpha asymmetry is widely used as a marker of brain lateralization and has been linked to conditions like depression and anxiety. This research provides a clearer picture of what normal, healthy alpha asymmetry looks like across the whole scalp and across early to middle adulthood, which could help researchers better interpret when asymmetry patterns deviate from the norm in clinical populations.
Caravaglios G, Caravaglios L, Vestini M, Di Maria G, Muscoso E. (2026). Topographic gradients of resting-state EEG alpha asymmetry: Network-specific lateralization and age-related dedifferentiation in healthy adults.. International journal of psychophysiology : official journal of the International Organization of Psychophysiology. https://doi.org/10.1016/j.ijpsycho.2026.113459