Posterior SEEG sites show higher low-frequency peaks and greater alpha relative to theta

We tested a pre-registered prediction of a posterior-to-anterior frequency gradient in human stereo-electroencephalography (SEEG). The analysis used archived per-pair spectra from 51 patients with bipolar depth recordings during free recall (OpenNeuro ds004789, session 0, 0–1.6 s after word onset): 4,780 pairs, with 26 log-spaced frequency bins. After removing a 1/f fit, we measured each pair's residual peak frequency and alpha-minus-theta residual power, then tested within-patient Spearman correlations with the dataset's tal.y coordinate (positive anterior). Across 40 patients, peak frequency decreased toward anterior sites (mean rho −0.161, 95% CI −0.254 to −0.066; 28/40 negative; Holm-adjusted sign-flip p = 0.0022). Across 42 patients, alpha-minus-theta balance also decreased toward anterior sites (mean rho −0.264, 95% CI −0.351 to −0.169; 35/42 negative; Holm-adjusted p = 0.0001). Pooled median peak frequency was 9.7 Hz posterior to −20 mm and 7.2 Hz at or anterior to 20 mm. The alpha-theta result remained with controls for lateral and vertical position, in neocortical gray-matter pairs, and with raw y coordinates. The peak-frequency result remained with positional controls and raw y coordinates, but was not significant in neocortical gray-matter pairs alone (rho −0.107, p = 0.086). Aperiodic exponent and beta residual power showed no gradient. These task-state findings come from one dataset with non-uniform clinical sampling; evoked responses were present, spectral resolution was coarse, and no phase analysis was done. A coordinate correlation does not establish a traveling wave.

stereo-electroencephalography · SEEG · low-frequency oscillations · alpha · theta · free recall · spatial gradient · human electrophysiology