In six SEEG patients, polarity reversal slightly reduced CCEP similarity, and mixed-tissue pairs evoked more responses after distance control

We examined whether reversing monophasic single-pulse polarity changes cortico-cortical evoked potentials (CCEPs), and whether stimulation-site tissue predicts responses after distance control. We analyzed one SPESclin run from each of six patients in OpenNeuro ds005448 v1.0.0: 184 contact pairs with at least one responsive channel. For N1 waveforms (15–100 ms), same-polarity similarity was r = 0.322 and reversed-polarity similarity was r = 0.270 (difference 0.052, 95% CI 0.004–0.122); four of six patients had a positive difference. The late-window difference was 0.035 (95% CI 0.003–0.079), positive in all six patients, and was the only primary result with patient-level exact p < 0.05 (p = 0.031). Two patients contributed most of the N1 effect, while repeat similarity was low (r about 0.3), so trial noise was much larger than the polarity effect. In a distance- and patient-adjusted logistic model, pairs with a white-matter-labelled contact (score 0.5) had higher response odds than gray-matter pairs (odds ratio 2.28, 95% cluster-bootstrap CI 1.54–3.34). The within-patient rank test without distance adjustment was not significant (4/5 positive, exact p = 0.375). There were no pairs with both contacts in white matter. Results are limited to six of eight patients, one run per patient, five pulses per polarity, monophasic 1–2 mA stimulation, threshold-based detection without visual review, and dataset tissue labels that were not checked against imaging. The possible long-range tissue effect was not distinguished from volume conduction or residual artifact.

SEEG · single-pulse electrical stimulation · cortico-cortical evoked potentials · pulse polarity · white matter · intracranial EEG · OpenNeuro