Theta-HFA coupling was not detected in 51 SEEG patients, but unreliable maps prevent rejecting spectral tilt

The spectral-tilt account proposes that the theta decrease and high-frequency activity (HFA, 70–150 Hz) increase in the subsequent memory effect (SME) reflect one broadband process. We tested whether bipolar pairs with a larger HFA SME also had a larger theta decrease in 51 of 54 pure-SEEG participants in the OpenNeuro RAM FR1 dataset (session 0), using archived per-word log10 band power from 0–1.6 s after word onset. After removing list and serial-position means, H1 coupling was the across-pair theta–HFA t-map correlation minus a 500-permutation within-list label null. Its mean Fisher z was −0.040 (95% CI −0.081 to +0.001; sign-flip p=0.057; Holm p=0.115). The odd/even-list cross-half correlation was −0.019 (95% CI −0.050 to +0.011; p=0.22). Neither test supported coupling. However, HFA split-half map reliability was absent (−0.015, p=0.61), and theta reliability was marginal (+0.057, p=0.061); under the preregistered interpretation rule, this null does not count as evidence against spectral tilt because the maps were too noisy to detect true coupling. Mean HFA SME was also absent (t=−0.01, p=0.85), while theta, alpha, and beta decreased (p≤0.008). Exploratory results showed positive low-gamma–HFA coupling (+0.073, Holm p=0.013) and negative theta–low-gamma coupling (−0.058, Holm p=0.050). These patterns need a preregistered test in a new sample. Limits include a single 1.6 s window, non-independent pairs that share contacts, half-data reliability estimates, unequal pair coverage, and archived features that were not re-extracted from raw EDF files.

subsequent memory effect · SEEG · free recall · spectral tilt · theta · high-frequency activity · split-half reliability · permutation test