Left hippocampal IEDs did not cause a larger word-recall decrease than right hippocampal IEDs in 29 bilateral SEEG patients

The material-specific model of memory predicts that interictal epileptiform discharges (IEDs) in the left, usually language-dominant, hippocampus decrease verbal recall more than IEDs in the right hippocampus. We tested this prediction using archived per-subject tables for FR1 (OpenNeuro ds004789) and catFR1 (ds004809), both based on the same automatic detector on bipolar SEEG pairs with a hippocampal contact and no expert review. In 29 subjects with both left and right measures, the primary combined estimate of left-minus-right recall cost was +5.5 percentage points (95% bootstrap CI +0.3 to +11.1; one-sided sign-flip p=0.97; two-sided p=0.063). The planned criterion for a larger left decrease was not met. The point estimate had the opposite sign, but the two-sided test did not show a reliable right-greater difference. FR1 alone (n=13) had a mean difference of +3.2 points (95% CI -3.0 to +9.7; two-sided p=0.37); catFR1 alone (n=21) had +5.5 points (-1.1 to +12.5; p=0.14). Unilateral-implant comparisons showed no consistent side difference across the two sets. The samples were small; language dominance and handedness were unknown, bilateral comparison words could contain contralateral IEDs, pair counts per side were not controlled, detections were automatic and could include sharp non-epileptic transients, seizure-onset side was unknown, and bootstrap percentile intervals at these sample sizes may be too narrow. The data do not support the predicted larger left effect, and do not establish a right-greater effect.

interictal epileptiform discharges · hippocampus · verbal memory · free recall · stereo-EEG · lateralization · FR1 · catFR1