Shared contacts are associated with excess spectral-shape similarity in bipolar SEEG pairs

In archived RAM SEEG data, consecutive bipolar pairs that shared one contact had more similar 2–45 Hz spectral shapes than distance and same-shaft position predicted. The pre-registered difference-in-differences test estimated a mean excess of +0.075 Fisher z (95% CI +0.022 to +0.130; 34 of 53 patients positive; sign-flip p = 0.0089; Holm p = 0.0089). A secondary comparison with cross-shaft pairs matched by distance estimated +0.173 Fisher z (95% CI +0.117 to +0.230; 98 of 132 patients positive; Holm p = 0.0001). Dataset checks gave +0.052 in ds004789 (20/35, p = 0.14) and +0.121 in ds004809 (14/18, p = 0.022). Similarity was high in all classes because the aperiodic slope dominated spectral shape. The results indicate that adjacent bipolar pairs are not independent samples of local spectra and that including shared-contact pairs can overstate local similarity in distance-decay analyses. The primary test assumes equal distance decay within and across shafts. Only 53 of 229 parsed patients met the primary test’s pair-count requirements. Data were from epilepsy patients, one 60 s task segment, and MNI midpoints, without tissue labels.

stereo-EEG · bipolar pairs · shared contacts · spectral shape · spectral similarity · distance decay · intracranial EEG