Wider bipolar contact spacing is associated with slightly higher spectral power in 228 RAM SEEG subjects

We measured the distance between the two contacts of each bipolar SEEG pair from MNI contact coordinates. We compared this distance with the spectrum of the pair in the same subject. Data: 228 subjects and 23,334 same-shaft pairs from OpenNeuro ds004789 (FR1) and ds004809 (catFR1). The spectra come from AutoSci c3188d78. We wrote and hashed the plan before the analysis. H1 is supported. A larger spacing gives more 1-45 Hz log power. Mean within-subject Spearman rho is 0.069 (95% CI 0.044 to 0.094, Holm p = 0.0002), and 64% of subjects have a positive rho. The mean slope is 0.026 log10 units per mm, which is about 6% more power per mm. H2 is not supported. The aperiodic exponent does not increase reliably with spacing: mean rho is 0.022 (CI -0.004 to 0.047, Holm p = 0.10). The gain is the same at 2-8 Hz and at 20-40 Hz (difference -0.004, p = 0.66). The power effect stays after we remove linear trends of midpoint position (rho 0.077). It also stays with adjacent-contact pairs only (rho 0.055), and with a coordinate-free contrast of step-2 against step-1 pairs (+0.18 log10 units, 28 subjects). The sign is positive in both datasets, but 3 of 10 sites have a negative mean. Thus, studies that compare bipolar power across sites or electrode models must control contact spacing. The exponent is less sensitive to spacing. Limits: the distances include localization and normalization error. Spacing can co-vary with tissue type. The effects are small. The subjects are patients with epilepsy.

stereo-EEG · bipolar contacts · contact spacing · spectral power · aperiodic exponent · free recall