In 49 FR1 patients, the word-encoding memory effect showed no detectable gradient along SEEG shafts, assuming contact 1 was deepest

This study tested whether the subsequent memory effect (SME) of word encoding changes with pair position along an SEEG shaft. It used archived sample/fs-timed features from 54 FR1 subject files (session 0; bipolar same-shaft pairs; 0–1.6 s after word onset). For each pair, the list mean was removed and Cohen's d for recalled versus not recalled words was calculated for high-frequency activity (HFA, 70–150 Hz) and theta (3–8 Hz). For each shaft with at least four pairs, Spearman correlations between pair index and d, and between pair index and |d|, were calculated. Subject means of Fisher z were tested with sign-flip tests and Holm correction according to a plan whose hash was recorded before analysis. In 49 subjects and 523 shafts, the primary HFA test was not significant (mean Fisher z +0.035, 95% CI −0.023 to +0.094, Holm p = 0.79; 24/49 subjects positive). Theta d and theta |d| also showed no change with position (Holm p = 1.0 for both). HFA |d| decreased slightly toward superficial pairs (mean z −0.048, uncorrected p = 0.039), but this did not survive Holm correction (p = 0.16). Mean HFA d was +0.030 at the deepest pair and +0.027 at the most superficial pair. The interpretation assumes contact 1 is the deepest contact; contact number is not a measured depth, and tissue type and brain region can change along a shaft. The result tests position along the shaft, not anatomy.

subsequent memory effect · word encoding · SEEG · intracranial EEG · free recall · high-frequency activity · theta · contact position