Modulation of neural oscillations by vagus nerve stimulation in posttraumatic multifocal epilepsy: case report

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The putative mechanism of vagus nerve stimulation (VNS) for medically refractory epilepsy is desynchronization of hippocampal and thalamocortical circuitry; however, the nature of the dose-response relationship and temporal dynamics is poorly understood. For greater elucidation, a study in a nonepileptic rat model was previously conducted and showed that rapid-cycle (RC) VNS achieved superior desynchrony compared to standard-cycle (SC) VNS. Here, the authors report on the first in-human analysis of the neuromodulatory dose-response effects of VNS in a patient with posttraumatic, independent, bilateral mesial temporal lobe epilepsy refractory to medications and SC-VNS who was referred as a potential candidate for a responsive neurostimulation device. During stereotactic electroencephalography (SEEG) recordings, the VNS device was initially turned off, then changed to SC-VNS and then RC-VNS settings. Spectral analysis revealed a global reduction of power in the theta (4–8 Hz) and alpha (8–15 Hz) bands with both SC- and RC-VNS compared to the stimulation off setting (p < 0.001). Furthermore, in the alpha band, both SC- and RC-VNS were associated with greater global desynchrony compared to the off setting (p < 0.001); and, specifically, in the bilateral epileptogenic hippocampi, RC-VNS further reduced spectral power compared to SC-VNS (p < 0.001). The dose-response and temporal effects suggest that VNS modulates regional and global dynamics differently.

ABBREVIATIONS EEG = electroencephalography; fMRI = functional MRI; NREM = non–rapid eye movement; POD = postoperative day; RC = rapid cycle; SC = standard cycle; SEEG = stereotactic EEG; VNS = vagus nerve stimulation.

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Contributor Notes

Correspondence Adeel Ilyas: University of Alabama at Birmingham, AL. WHEN CITING Published online November 16, 2018; DOI: 10.3171/2018.6.JNS18735.Disclosures Dr. Pati has been a consultant for NeuroPace.

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