Identification of seizure onset zone and preictal state based on characteristics of high frequency oscillations

• High frequency oscillations (80–200 Hz) (HFO) may occur in all channels of intracranial recordings.
• Average HFO rate is higher within seizure onset zone and increase during the transition from interictal to preictal and to ictal period.
• Characteristics of HFO events within the seizure onset zone differ from those outside the seizure onset zone, and change during the interictal to ictal transition.

ObjectiveWe investigate the relevance of high frequency oscillations (HFO) for biomarkers of epileptogenic tissue and indicators of preictal state before complex partial seizures in humans.MethodsWe introduce a novel automated HFO detection method based on the amplitude and features of the HFO events. We examined intracranial recordings from 33 patients and compared HFO rates and characteristics between channels within and outside the seizure onset zone (SOZ). We analyzed changes of HFO activity from interictal to preictal and to ictal periods.ResultsThe average HFO rate is higher for SOZ channels compared to non-SOZ channels during all periods. Amplitudes and durations of HFO are higher for events within the SOZ in all periods compared to non-SOZ events, while their frequency is lower. All analyzed HFO features increase for the ictal period.ConclusionsHFO may occur in all channels but their rate is significantly higher within SOZ and HFO characteristics differ from HFO outside the SOZ, but the effect size of difference is small.SignificanceThe present results show that based on accumulated dataset it is possible to distinguish HFO features different for SOZ and non-SOZ channels, and to show changes in HFO characteristics during the transition from interictal to preictal and to ictal periods.