Region-specific high-frequency oscillations under propofol anesthesia: comparison of epileptogenic and functional cortex.

OBJECTIVE

To determine whether the rates of pathological and physiological high-frequency oscillations (HFOs; 80-200 Hz) differ between non-rapid eye movement sleep (NREM) and propofol anesthesia (PA).

METHODS

We retrospectively analyzed 11 patients with drug-resistant epilepsy who underwent chronic intracranial EEG monitoring and intraoperative EEG recording under PA. Among 761implanted electrodes, 29 sites were classified as epileptogenic cortex (EC), defined as seizure onset sites whose resection resulted in postoperative seizure freedom. Fifty-eight sites were classified as functional cortex (motor, somatosensory, visual, or language) based on electrical stimulation mapping. None of these 87 sites exhibited interictal spikes or overlapped between epileptogenic and functional categories. We examined whether PA altered HFO rates compared with NREM.

RESULTS

HFO rates remained stable between NREM and PA. HFO rates in epileptogenic and visual cortical sites were higher than those in other functional sites (p < 0.05). HFO rates were comparable between epileptogenic and visual cortical sites, with no significant differences in either state. Although the EC showed higher HFO rates than most functional cortices, the visual cortex displayed HFO rates comparable to the EC, with no significant differences in either state (NREM, p = 0.87; PA, p = 0.66).

CONCLUSION

Under both NREM and PA, the rate of pathological HFOs exceeded that of physiological HFOs, except those generated in the visual cortex.

SIGNIFICANCE: Distinct patterns of pathological and physiological HFOs may aid interpretation of intraoperative recordings obtained under PA, although caution is required for occipital HFOs.