Detection of recurrent activation patterns across focal seizures: Application to seizure onset zone identification

Objective: We introduce a method that quantifies the consistent involvement of intracranially monitored regions in recurrent focal seizures.

Methods: We evaluated the consistency of two ictal spectral activation patterns (mean power change and power change onset time) in intracranial recordings across focal seizures from seven patients with clinically marked seizure onset zone (SOZ). We examined SOZ discrimination using both patterns in different frequency bands and periods of interest.

Results: Activation patterns were proved to be consistent across more than 80% of recurrent ictal epochs. In all patients, whole-seizure mean activations were significantly higher for SOZ than non-SOZ regions (P<0.05) while activation onset times were significantly lower for SOZ than for non-SOZ regions (P<0.001) in six patients. Alpha-beta bands (8-20Hz) achieved the highest patient-average effect size on the whole-seizure period while gamma band (20-70Hz) achieved the highest discrimination values between SOZ and non-SOZ sites near seizure onset (0-5s).

Conclusions: Consistent spectral activation patterns in focal epilepsies discriminate the SOZ with high effect sizes upon appropriate selection of frequency bands and activation periods.

Significance: The present method may be used to improve epileptogenic identification as well as pinpoint additional regions that are functionally altered during ictal events.