A 20 Hz-locked artifact appears in all contacts of one W3 SEEG run and places lines in the high-gamma band

We examined one 404 s SEEG run (160 contacts, 2048 Hz) from OpenNeuro ds004993 v1.1.2: subject W3, session iemu, task timit4, acquisition B8, run 01. All contacts showed narrow lines at multiples of 20 Hz, including lines at 80, 100, 120 and 140 Hz within the 70–150 Hz high-gamma band used in speech BCIs. At 80 Hz, median line prominence was 2.58 log10 units (about 380 times local background) in the original reference and 1.74 (about 55 times) after common average reference (CAR). The artifact had seven on blocks of about 33 s and off blocks of about 27 s. Comb lines at 80, 100, and 120 Hz occupied 6.2% of high-gamma bins and carried a median 10.8% of CAR high-gamma power per contact (10th–90th percentile 6.7%–31.0%; maximum 44.5%). A corrected state rule labeled 126 sentences as 64 ON, 47 OFF, and 15 MIXED. We assume the source was the implanted vagus nerve stimulator (VNS), based on the dataset description; there were no device logs and the source was not proven. A pre-specified CAR-based search did not detect the 20 Hz fundamental, so the planned test of decoder performance was not run. The reported analyses are exploratory and descriptive, with no statistical test. This is one subject and one run; other runs and subjects were not checked.

SEEG · stimulation artifact · vagus nerve stimulation · high-gamma · brain-computer interface · spectral lines · common average reference · OpenNeuro