After lag calibration, phase at bipolar pairs two contacts apart differed by 63–71° in 21 awake SEEG patients

This analysis estimated the phase error caused by spatial separation between bipolar pairs on the same SEEG shaft, as a best-case reference for phase-targeted stimulation. It used 60-second middle segments from the first session of 21 of 24 awake patients in OpenNeuro ds005624. Signals were analyzed in delta (1–4 Hz), theta (4–8 Hz), alpha (8–13 Hz), and beta (13–30 Hz) bands with fourth-order Butterworth zero-phase filtering and the Hilbert transform. For pairs two contacts apart, median phase error after one lag calibration on the first 29 seconds was 63°, 64°, 66°, and 71° in the four bands, respectively, for the last 29 seconds; calibration reduced error in all 21 patients in every band (Wilcoxon p = 9.5×10⁻⁷). No patient had calibrated error below the approximately 45° causal phase-estimator reference in any band. Amplitude gating reduced group errors to 48–56°. Error increased with separation in all patients (median Spearman ρ = 0.9–1.0, p = 4×10⁻⁵). Significant imaginary coherency occurred in 10–12% of two-step pairs of pairs, compared with 0% under the shift null (p ≤ 9×10⁻⁵); the median folded lag among these pairs was 45–56°. Most along-shaft coupling was therefore zero-lag or weak, while a minority had consistent non-zero lag. These results suggest that phase at a pair two contacts away is a poor proxy for phase at a stimulation target, although reading at the target pair or calibrating polarity at an adjacent pair may help. The analysis is limited to 60 seconds per patient, patients with epilepsy, an unknown task phase, no interictal discharge removal, contact steps rather than millimeters, non-causal filters, no real stimulation, and 21 of 24 subjects. The S3 source files are identified by recorded byte ranges and hashes, but the exact dataset release is uncertain.

SEEG · phase error · phase calibration · bipolar recording · imaginary coherency · phase-targeted stimulation · OpenNeuro ds005624