Theta and HFA subsequent memory effects have dissociable spatial patterns in SEEG free recall

In 24 patients with stereoelectroencephalography (SEEG), theta power decreases and high-frequency activity (HFA) increases for later-recalled words had reliable but nearly uncorrelated spatial patterns across bipolar pairs. Using archived, sample/fs-timed features from 26 pure-SEEG participants in the FR1 session of the Delayed Free Recall of Word Lists dataset, we compared recalled and not-recalled words in independent halves. In the primary odd/even-list split (24 participants, 1,786 pairs), theta and HFA pattern reliabilities were r=0.242 (19/24 positive; Holm p=0.00015) and r=0.143 (19/24 positive; Holm p=0.023). The cross-band, cross-half correlation was 0.023 (12/24 positive; p=0.43); the disattenuated correlation was 0.12 (95% CI -0.17 to 0.50). An alternating-word split gave a similar result (23 participants, 1,670 pairs; disattenuated correlation 0.05, 95% CI -0.22 to 0.35). The confidence intervals exclude the -1 correlation predicted by a single shared pair-level tilt process and include zero, consistent with dissociable spatial patterns. The estimates remain imprecise and allow moderate negative or positive associations. The analysis covers bipolar-pair resolution, one 0–1.6 s post-word window, one session and FR1 only; it does not test within-pair mechanisms.

SEEG · free recall · subsequent memory · theta · high-frequency activity · spectral power · bipolar pairs · spatial pattern · reliability