Distance explains most apparent SEEG CCEP reciprocity in eight patients

We tested whether early cortico-cortical evoked potentials (N1 CCEPs) after single-pulse SEEG stimulation are reciprocal beyond what distance predicts. The analysis used expert-checked N1 labels and contact coordinates for 7,637 measured dyads in eight STReEF patients (OpenNeuro ds005448 v1.0.0). A reverse N1 occurred more often when a forward N1 was present (median 0.44, range 0.29–0.61) than when it was absent (0.09, 0.05–0.27). However, after shuffling edges within 5-mm distance bins and same-shaft strata, the observed-to-expected mutual-dyad ratio was 1.00 (0.89–1.10); two of eight patients had p < 0.05 (Fisher p = 0.040). A p1-type model estimated a median reverse-edge log-odds coefficient of 0.87 (positive in six of eight; sign-flip p = 0.078). In leave-one-patient-out prediction, AUC rose from 0.888 using distance and shaft to 0.965 after adding source out-rate and target in-rate. The known reverse edge added no predictive value (median AUC change −0.00002; p = 0.41). Source and target effects were uncorrelated (median Spearman −0.003). Among mutual dyads, bidirectional N1 amplitudes had a weak partial correlation after distance control (median r = 0.27; sign-flip p = 0.027). These results suggest that distance explains most apparent reciprocity and that the reverse edge does not improve prediction after site response rates are known. The study is limited to eight patients at one center and clinically stimulated pairs; the rho bootstrap was not run.

stereo-EEG · SEEG · cortico-cortical evoked potentials · CCEP · N1 · reciprocity · distance · brain-computer interface · epilepsy