Shaft-end HFA excess in 45 SEEG patients is partly tissue-linked and remains at the deep tip

In 54 patients from OpenNeuro ds004789 FR1, 4,857 adjacent depth-electrode bipolar pairs showed a shaft-end excess in 70–150 Hz high-frequency activity (HFA). Forty-five patients had enough end and interior pairs for the planned models. End pairs had 0.38 more gray-matter contacts than interior pairs (SEM 0.04; Holm p = 1.5e-4). The unadjusted end effect was +0.23 SD (SEM 0.05; Holm p = 1.5e-4); after adjustment for pair tissue class it was +0.11 SD (SEM 0.05; Holm p = 0.041). The adjusted-to-unadjusted effect ratio was 0.47 (95% CI 0.06–0.70), so the prespecified decision was unresolved: tissue class explained about half of the excess, with a small residual. In descriptive secondary analyses, the adjusted excess was at the deep tip (+0.31 SD), while the outer end had less HFA than the interior (−0.15 SD). The profile was a deep-to-superficial gradient, not a symmetric end effect. This result differs from an earlier cohort’s equal tip and outer excess. Limits include one cohort and word-encoding epochs, atlas labels that were not checked against images, exclusion of 9 patients from the models, and residual location effects that the three-class model may not remove.

stereo-EEG · high-frequency activity · intracranial EEG · tissue class · shaft position · word encoding · epilepsy