White-matter SEEG power decreased slightly with distance from gray matter, mostly at the first contact step

In 119 patients with RAM stereo-EEG (SEEG), 2–40 Hz power in white-matter (WW) bipolar pairs showed a small negative within-patient association with MNI distance to the nearest gray-matter (GM) contact (mean Spearman rho −0.073, 95% CI −0.125 to −0.021, p = 0.0088). The association with same-shaft contact steps was −0.120 (p = 0.0001). The decrease was mostly between the contact step next to GM and step 2, about 0.1 log10, roughly one quarter of the same-patient gray–white difference (0.43 log10). Farther WW pairs had flatter aperiodic spectra, less relative delta, and more relative beta and gamma; relative theta and alpha were not associated after correction. The OLS slope check was not significant, and catFR1 alone (16 patients) did not show the effect. Tissue labels were atlas labels in MNI space, not individual MRI segmentation; boundary label error can produce the same pattern, and shaft position was not controlled. The data were 60 seconds at the start of a memory task in epilepsy patients; seizure-onset contacts were not removed. The design cannot separate volume conduction, boundary label error, remote sources, or noise.

stereo-EEG · white matter · gray matter · bipolar recording · volume conduction · power spectrum · spectral shape · memory · intracranial EEG