Alpha power and brain functional connectivity as signatures of altered network dynamics in functional/dissociative...

Functional/dissociative seizure (FDS) disorder presents diagnostic challenges due to its complex semiology and the lack of positive diagnostic biomarkers. Current evidence suggests that specific patterns of brain activity and distinct dynamics in the brain network may underlie the neurobiological mechanisms of FDS.

We retrospectively analyzed ictal EEG recordings from 46 patients with FDS, in three different conditions: during resting wakefulness (RW), during resting while having eyes closed (EC), and during functional/dissociative seizures of variable semiology (FDS). The occipital EEG in the alpha band (8-13 Hz) was assessed in terms of power and functional connectivity, quantified by debiased weighted phase lag index (dwPLI). Heart rate was also analyzed across conditions. Statistical comparisons were performed via paired permutation testing with Benjamini-Hochberg correction for multiple comparisons, complemented by Bayes factors for the key FDS-EC comparisons.

EEG during FDS exhibited significantly higher occipital alpha power than RW (p = 0.0003) and levels not significantly different from EC, with moderate Bayesian evidence for the absence of a difference (BF01 = 6.1). Alpha power was elevated across all FDS subtypes and was, paradoxically, numerically highest in hypermotor seizures, although subtype differences did not survive correction for multiple comparisons. Control analyses showed that the alpha power did not significantly differ across video-rated states of eyes during FDS (open, intermittently closed, closed), including when conditions were matched for eye state. Functional whole-brain connectivity in the alpha band was intermediate between the two resting conditions, being higher during FDS than during RW but lower than during EC. Heart rate was highest during FDS, with a non-significant tendency toward higher rates in hypermotor than atonic FDS. No significant correlation was found between occipital alpha power and heart rate during FDS.

Our findings suggest that FDS are characterized by a paradoxical hypersynchronization in the EEG alpha band, similar to EC, despite concurrent motor activity. Increased functional alpha connectivity, simultaneous with elevated heart rate during FDS, suggests that FDSs involve altered brain network dynamics rather than simple alpha power suppression by voluntary motor activity. These findings may aid in developing positive biomarkers for FDS diagnosis.