Word-locked evoked responses mark larger subsequent memory effects in SEEG free recall

We tested whether the subsequent memory effect (SME) in SEEG free recall is larger in bipolar pairs with a word-locked evoked response. We used archived per-word features from OpenNeuro ds004789 (RAM FR1), session 0: 25 pure-SEEG subjects and 1,851 bipolar pairs. Epochs were 0–1.6 s from events.tsv sample/fs. Bands were theta (3–8 Hz) and high-frequency activity (HFA, 70–150 Hz); tilt was z(HFA) − z(theta). For each pair, we calculated a Welch t statistic (recalled minus not recalled). Within each subject, we measured Spearman rho across pairs between log evoked index and pair t. A sign-flip test across subjects and Holm correction covered three outcomes. The mean rho was +0.215 for tilt (95% CI +0.155 to +0.274; 24/25 positive; Holm p=0.00015), −0.208 for theta (CI −0.300 to −0.113; 19/25 negative; p=0.0008), and +0.092 for HFA (CI +0.023 to +0.159; 15/25 positive; p=0.017). In the pre-registered, uncorrected tercile comparison, top minus bottom third mean pair t was +0.58 for tilt (CI 0.40 to 0.75; 22/25; p=5e−5), −0.57 for theta (CI −0.81 to −0.33; p=0.0003), and +0.27 for HFA (CI 0.08 to 0.47; p=0.011). Adjustment for raw signal size gave similar correlations. A post-hoc within-atlas-region analysis also retained the association (tilt z +0.17, CI 0.09 to 0.25, 19/24, p=0.0003; theta −0.15, p=0.0009; HFA +0.10, p=0.026). The evoked index does not use recall labels and may rank pairs for memory decoding, but no decoder was tested. The index and SME use the same words. A recall-dependent ERP may affect both, especially theta; theta power also contains ERP power. The study used only FR1 session 0 and one time window, and lacked raw signals to calculate the index from separate words. Correct EDF timing is assumed to be events.tsv sample/fs. These results show an association in this dataset and analysis, not validated decoder performance.

SEEG · subsequent memory effect · evoked response · free recall · theta · high-frequency activity · memory decoding