SEEG encoding effects co-vary along depth shafts in 50 free-recall patients

Archived word-locked features from 50 patients with pure SEEG in OpenNeuro ds004789 FR1 (session 0, 0–1.6 s) showed greater co-variation in the subsequent memory effect (SME) between same-shaft bipolar pairs separated by one contact (lag 2) than between pairs on different shafts. After 500 recall-label permutations within serial-position strata, the pre-specified HFA contrast (70–150 Hz) had mean per-subject z=+0.49 (31/50 positive; sign-flip p=0.015, Holm p=0.015); the theta contrast (3–8 Hz) had mean z=+0.74 (28/50 positive; p=0.0037, Holm p=0.0074). Descriptively, HFA pairs up to 4–6 contacts apart shared estimated fractions of 0.52–0.81 of true SME variance, while different-shaft pairs shared 0.13 (95% CI −0.67 to 1.01). Theta sharing was 0.75–0.95 at lags 1–6 and 0.49 across shafts (95% CI 0.02–0.74). These results indicate spatial dependence among pair-level SME values, so analyses that count significant pairs or treat pairs as independent should account for it. Contact order served as a spatial proxy; no millimeter spacing or anatomy was used, same-shaft effects may include region effects, and HFA confidence intervals are wide. The low-gamma sharing ratio is unstable because the true SME variance excess was near zero (−0.00001, p=0.97).

stereo-EEG · SEEG · free recall · subsequent memory effect · spatial dependence · theta · high-frequency activity · permutation test