Altered interictal alpha-band organization in childhood absence epilepsy

Interictal background EEG in childhood absence epilepsy (CAE) may appear normal. We asked whether drug-naive children with CAE differ from controls in alpha frequency and the regional distribution of phase-lagged synchronization, and how these differences depend on participant-specific surrogate baselines and analysis frequency.

We analyzed eyes-closed resting EEG (19 channels, 26 s) from 49 drug-naive children with CAE and 83 controls. Individual alpha frequency (IAF) was estimated by spectral parameterization of posterior channels. Weighted phase-lag index (wPLI) at 12 Hz was summarized globally and as the frontal-posterior log-ratio λ_FP = ln(wPLI_F/wPLI_P), where F and P denote frontal and posterior within-region means. Participant-specific baselines were obtained from 100 circular-shift surrogates, preserving each channel's wavelet-coefficient sequence up to circular translation while altering inter-channel alignment. Group comparisons used studentized permutation tests. The regional contrast was also evaluated at each participant's IAF.

IAF was lower in patients (8.80 versus 9.42 Hz; p = 0.002). At 12 Hz, controls showed posterior predominance of synchronization (λ_FP = -0.352), which was largely removed by circular shifting (-0.036), whereas patients' mean regional balance was near zero. After baseline subtraction, the patient-minus-control difference in λ_FP was 0.332 (95 % CI [0.181, 0.483]; p < 0.001; Hedges' g = 0.79). In the 131 participants with identifiable IAF, the contrast was 0.316 at 12 Hz and 0.124 at IAF (p = 0.139). A direct comparison using within-participant changes supported a larger contrast at 12 Hz (difference 0.192, 95 % CI [0.017, 0.367]; exploratory, unadjusted p = 0.032). The global wPLI difference after baseline subtraction remained uncertain (-0.021, 95 % CI [-0.044, 0.001]; p = 0.069).

Drug-naive CAE was associated with slower alpha activity and reduced posterior predominance of phase-lagged synchronization at 12 Hz. Circular shifting largely removed the controls' posterior predominance, supporting a difference in regional organization sensitive to inter-channel alignment. The smaller contrast at IAF indicates that analysis frequency materially affects this finding, without establishing that alpha slowing alone explains it.