High Frequency Oscillations (HFOs) are a powerful biomarker of epileptic tissue and potentially of epileptogenicity. But their utility is hampered by requiring long-term spontaneous recordings and difficulties detecting HFOs non-invasively. In this study, we investigate the possibility of evoking and recording HFOs through scalp electroencephalography in humans.
Ten patients with depth electrodes implanted to localize their epileptic focus underwent pseudo-random multi-region single pulse electrical stimulation (SPES) with simultaneous intracranial EEG recording during sleep.
SPES in neocortical regions evoked concurrent intracranial and scalp HFOs in half of them. In these patients, stimulation delivered to the seizure onset zone (SOZ) but not to a contralateral channel evoked scalp HFOs. Importantly, detection only required the rapid semi-automatic analysis of a few seconds per recording. This initial study confirmed the presence of evoked HFOs on the scalp and in the intracranial SOZ following stimulation.
With probing stimulation, we could analyze averaged stimulation evoked HFOs, which increased signal to noise in limited the analysis window. Understanding the characteristics of evoked scalp HFOs is the first step towards its clinical use as a localizer and possibly predictor of epileptogenesis.