Spatiotemporal EEG Dynamics Across Early and Late Preictal Periods in Pediatric Focal Epilepsy

Objective: This study aimed to quantify the temporal and spatial dynamics of preictal cortical networks in pediatric refractory focal epilepsy using scale-independent EEG measurements. Method: For this purpose, the preictal (−35 to −5 min), interictal, early preictal (−35 to −20 min), and late preictal (−20 to −5 min) periods were examined in long-term scalp EEG recordings from pediatric patients in the CHB–MIT database. For the selected segments, the detrended fluctuation analysis (DFA) scale exponent, median power frequency (MPF), and aperiodic 1/f exponent (β) were calculated using SpecParam/FOOOF and IRASA. The metrics were summarized on an individual basis and analyzed using two-way repeated measures ANOVA with Šídák-corrected post-hoc tests and topographic mapping. Findings: The preictal period was characterized by increased DFA-α and MPF in fronto-temporal regions compared to the interictal period; during the interictal period, MPF foci shifted to posterior areas. Aperiodic β values showed steepening in frontal regions during the preictal period and exhibited a posterior-temporal gradient during the interictal period. Critically, during the transition from the early to late preictal period, fronto-temporal DFA-α and MPF values decreased, accompanied by a posterior-to-anterior spread of aperiodic β steepening. Conclusion: These findings indicate that cortical networks experience a collapse in long-range temporal correlations and a reorganization of the aperiodic spectral structure as seizure onset approaches. The observed loss of complexity, spectral slowing, and frontal aperiodic steepening, occurring simultaneously, suggest a heterogeneous nature of the preictal process and highlight the potential of scale-independent metrics in monitoring seizure risk.