Gray matter-only pairs showed a recall decrease, but evidence did not establish a tissue difference in open-loop FR2/catFR2

This exploratory analysis tested whether the later recall effect of open-loop encoding stimulation differed by tissue at the stimulation contacts in RAM FR2 and catFR2. It used behavioral events and atlas labels from OpenNeuro ds005489 (FR2, version 1.0.3) and ds005491 (catFR2, version 1.0.0); no intracranial EEG signals were used. The unit was one subject by one stimulation site (anode-cathode pair), with sessions pooled. For depth-electrode pairs, mean d_item was -4.5 percentage points (pp) for gray matter-only pairs (20 units, 18 subjects; 95% CI -7.6 to -1.7; sign-flip p=0.007) and -0.8 pp for pairs with at least one white matter contact (16 units, 14 subjects; 95% CI -3.9 to +2.2; p=0.62). The primary white matter minus gray matter contrast was +3.7 pp (95% CI -0.6 to +8.0; permutation p=0.11). Its sign was positive in all nine sensitivity analyses, but none had p<0.05. Thus, the data show a recall decrease in gray matter-only pairs but do not show a reliable tissue difference. Atlas contact labels have localization uncertainty of a few millimeters; tissue labels were missing for 12 of 48 depth units, grid and strip units were not tested, and the sample had about 80% power only for differences of approximately 6.5 pp or larger.

open-loop stimulation · free recall · memory · gray matter · white matter · intracranial EEG · RAM · FR2 · catFR2