Moving beyond spike detection: High frequency-driven masking improves seizure onset zone localization in intracranial
Amir Hossein Ayyoubi1,2, Behrang Fazli Besheli2, Valentina Hrtonova2,3
1Department of Bioinformatics and Computational Biology, University of Minnesota, Minneapolis, Minnesota, USA.
Objective:
Interictal epileptiform spikes (IESs) are widely used biomarkers of epileptogenic tissue in presurgical epilepsy evaluation. However, their reliability for seizure onset zone (SOZ) localization in high-density intracranial electroencephalography (iEEG) remains inconsistent. It is underexplored whether this variability reflects methodological differences across detection algorithms or a limitation of IESs as a biomarker. This study evaluates whether IES detection alone provides sufficient spatial specificity for accurate SOZ localization in iEEG.
Methods:
We systematically benchmarked eight established IES detection algorithms using iEEG recordings from 35 patients with drug-resistant focal epilepsy. To provide a clinically meaningful reference, algorithm performance was evaluated against the clinically defined SOZ. To refine detection outputs and move beyond only IES detection, we applied masking strategies to isolate informative IES subsets based on rate, amplitude, frequency, and co-occurrence with high-frequency oscillations (HFOs). Conceptually, masking acts as a spatial refinement strategy that progressively restricts diffuse IES activity to more focal, pathologically relevant event populations.
Results:
Despite substantial variability in detection characteristics, SOZ localization performance (ratio of events originating from SOZ divided by total number of events) converged within a narrow range (.23-.51), suggesting that IESs exhibit an intrinsic ceiling in SOZ localization performance when used alone. Amplitude-based masking yielded modest improvements, whereas frequency-based masking reduced performance. In contrast, IES-HFO co-occurrence markedly improved localization, particularly when combined with rate-based masking, achieving a median SOZ localization ratio of .89, exceeding IESs (.37) and HFOs (.63) evaluated independently.
Significance:
These findings demonstrate that IES-based SOZ localization may require moving beyond detection-only approaches. The integration of informed, biomarker-driven masking strategies provides a more robust framework for identifying the activity most relevant to the epileptogenic network and paves the way for future incorporation into the clinical decision-making pipeline.
