The Immediate Effects of Vagus Nerve Stimulation in Intractable Epilepsy: An Intra-operative Electrocorticographic Analysis

Abstract

The purpose of this study was to investigate whether and how vagus nerve stimulation (VNS) reduces the epileptogenic activity in the bilateral cerebral cortex in patients with intractable epilepsy. We analyzed the electrocorticograms (ECoGs) of five patients who underwent callosotomy due to intractable epilepsy even after VNS implantation. We recorded ECoGs and analyzed power spectrum in both VNS OFF and ON phases. We counted the number of spikes and electrodes with epileptic spikes, distinguishing unilaterally and bilaterally hemispherically spread spikes as synchronousness of the epileptic spikes in both VNS OFF and ON phases. There were 24.80 ± 35.55 and 7.20 ± 9.93 unilaterally spread spikes in the VNS OFF and ON phases, respectively (P = 0.157), and 35.8 ± 29.21 and 10.6 ± 13.50 bilaterally spread spikes in the VNS OFF and ON phases, respectively (P = 0.027). The number of electrodes with unilaterally and bilaterally spread spikes in the VNS OFF and ON phases was 3.84 ± 2.13 and 3.59 ± 1.82 (P = 0.415), and 8.20 ± 3.56 and 6.89 ± 2.89 (P = 0.026), respectively. The ECoG background power spectra recordings in the VNS OFF and ON phases were also analyzed. The spectral power tended to be greater in the highfrequency band at VNS ON phase than OFF phase. This study showed the reduction of epileptogenic spikes and spread areas of the spikes by VNS as immediate effects, electrophysiologically.

Human intracranial recordings reveal distinct cortical activity patterns during invasive and non-invasive vagus nerve stimulation

“…For example, if a particular desired outcome has been shown to correlate with an increase in theta band power, this target neuromodulatory state may be attainable by application of either 30 Hz iVNS or low amplitude taVNS. Though our sample size (n = 7) is comparable to recent studies 21,22 (though note that we sampled from a much larger set of electrodes, n = 1140), the high degree of variability we observed suggests that further work is needed to understand the multiple factors that contribute to different effects across modalities and individuals. It is also important to note that while in this study we elected to focus on acute changes in low-frequency spectral band power evoked by VNS, there are other complementary measures that were not examined here, such as functional connectivity 22 and vagal-evoked potentials 55 , across multiple time scales (i.e., acute vs. chronic effects 4 ).…”

“…We also observed that different cortical networks exhibited different responses to VNS (Fig. 2), which may explain why prior iEEG studies that only had access to a limited number of electrodes, produced conflicting results 20,21 . However, it is important to note that this caveat may apply to our findings as well.…”

“…There have also been a small number of intracranial electroencephalography (iEEG) studies that have benefited from the superior signal-to-noise ratio of direct cortical recordings, but these have also produced inconsistent results. In two recent iEEG studies on acute iVNS that used similar stimulation parameters, one reported decreases in lowfrequency spectral band power and no changes in high frequency broadband power 20 , while the other reported the opposite 21 . Similarly, an iEEG study investigating the effects of VNS amplitude on functional connectivity reported distinct patterns of effects across individuals 22 .…”

Motor Mapping with Functional Magnetic Resonance Imaging: Comparison with Electrical Cortical Stimulation

“…Technological limitations, such as electrical current spread of ECS, no recording of EMG, sensitivity of BOLD signal in fMRI, different spatial resolution of two modalities, patients' awareness, and difference of extremity sites, may affect the results. 16 , 17 ) In addition, fMRI evaluates “voluntary movement,” whereas ECS induces movement by an active stimulation of the cortex. Therefore, we need to consider that these two modalities are observing a completely different aspect of motor control.…”

Label-Free Functional Imaging of Vagus Nerve Stimulation-Evoked Potentials at the Cortical Surface

“…Recent fMRI findings showed distinct differences in effects between invasive VNS and transcutaneous VNS 18 . Additionally, invasive EEG studies on acute invasive VNS have found opposing effects of similar stimulation parameters on EEG spectral and broadband power 19 , 20 . A more recent finding suggests that while there may be variable results across cortical networks in the stereotactic EEG of different patients, in some individuals there are distinctly similar responses with certain stimulation paradigms 14 .…”