Pre-stimulus high-gamma did not reliably predict decision speed in five SEEG patients

We tested whether 70–150 Hz high-gamma activity (HGA) in the 0.5 s before random-dot motion onset predicted fast versus slow decisions in five SEEG patients from OpenNeuro ds006253. The analysis plan was fixed before neural results were computed. We used archived, binned log-HGA epochs and behavior, regressed log decision time on coherence and trial number, and classified residuals above or below each patient's median. A shrinkage LDA using all bipolar channels and five contiguous trial blocks gave a median AUC of 0.548 (3 of 5 patients above 0.5; exact one-sided sign-flip p = 0.31). No patient exceeded their circular-shift null at p < 0.05, so the pre-set decision rule was not supported. With raw decision time and shuffled folds, median AUC was 0.634 (4 of 5); trial number alone gave median AUC 0.556, consistent with slow session drift inflating apparent readiness information. The early stimulus window (0–0.25 s, late movers) gave median AUC 0.494. The sample includes five of 22 patients, selected by file size; an effect near AUC 0.55 cannot be excluded. The analysis uses HGA only, linear detrending, and offline decoding.

SEEG · high-gamma activity · decision time · random-dot motion · brain-computer interface · shrinkage LDA · cross-validation · session drift