In one patient, a post hoc 20 Hz VNS detector linked stimulation-on time to higher monopolar high-gamma power, while bipolar rereferencing reduced the rise

We examined whether vagus nerve stimulator (VNS) artifact affected 70–150 Hz stereo-EEG (SEEG) power and sentence responses in OpenNeuro ds004993. In subject W3, an exploratory check found an exact 20.00 Hz line in all channels; the preregistered detector had failed by selecting the 1/f low edge at 16 Hz. In the post hoc analysis with the detector fixed at 20 Hz, 155 of 404 one-second windows were labeled VNS-on. Median monopolar high-gamma power rose by 1.49 dB (155/160 channels >1 dB), while bipolar power rose by 0.07 dB (0/148 pairs >1 dB); all 148 bipolar effects were smaller in magnitude than the mean magnitudes of their two contacts (Wilcoxon p=4.9×10⁻²⁶). For 16 VNS-on and 42 VNS-off sentences (68 mixed sentences excluded), baseline-corrected monopolar responses differed by −0.48 dB (p=4×10⁻¹⁰), while uncorrected window power differed by +2.35 dB (p=3×10⁻¹¹). Bipolar baseline-corrected responses did not differ significantly (−0.19 dB, p=0.22); uncorrected power differed by +0.10 dB (p=0.042). The preregistered W2 test did not support sentence identification from high-gamma responses: accuracy was 0.20 versus 0.10 chance (permutation p=0.27). These are case-level findings from one patient for W3 and one for W2; channels and pairs are not independent, and the VNS detector is post hoc.

stereo-EEG · vagus nerve stimulation · high gamma · bipolar rereferencing · artifact · sentence responses · OpenNeuro ds004993