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Interhemispheric EEG connectivity before and after callosotomy

Poster Session C - Sunday, March 8, 2026, 5:00 – 7:00 pm PDT, Fairview/Kitsilano Ballroom

Henri Etel Skinner^1,2 (), Lukas J. Volz⁴, Tyler Santander^1,2, Selin Bekir¹, Christian G. Bien³, Michael S. Gazzaniga¹, Michael B. Miller^1,2, Barry Giesbrecht^1,2; ¹University of California, Santa Barbara, ²Institute for Collaborative Biotechnologies, ³Krankenhaus Mara, Bethel Epilepsy Center, Medical School OWL, Bielefeld University, Germany, ⁴Medical Faculty, University of Cologne, University Hospital Cologne, Germany

Callosotomy, a surgery involving the severing of the corpus callosum, is a re-emerging treatment for severe and pharmacologically intractable epilepsy. We recently reported that a callosotomy patient with minimal spared fibers had conserved functional connectivity measured with fMRI (Santander et al., 2025). Here, we report an analysis of functional connectivity measured with electroencephalography (EEG). We investigated both intra- and interhemispheric connectivity pre-callosotomy and after partial or full callosotomy. Patients recordings reported here include LJ (1 Pre, 3 Full), EM (1 Pre, 1 Partial), and BT (1 Partial). Clinical EEG recordings with electrodes (18 used) placed according to the 10-20 system and recorded at 512 Hz. Data were analyzed from eyes-open and eyes-closed conditions. For each recording session EEG was band-pass filtered (0.1-30Hz), epoched by condition, baseline-corrected, and underwent threshold rejection (+/-80mV). Correlations were computed for each electrode pair and converted to R2 to estimate the shared variance across pairs of electrodes. T-tests were performed for each recording session between inter and intra hemispheric R2 which yielded a significant difference (p<.05) for all but one recording, such that intrahemispheric shared variance was higher than interhemisphere (Cohen's d: min=0.088, max=0.271). For the only full callosotomy patient in this sample (LJ), this difference was not significant in the first recording post-callosotomy (57 days) (open: t(151)=1.56, p=0.12, closed: t(151)=0.887, p=0.377). Results suggest connectivity measured by EEG may be dependent both on the completeness of the callosotomy and time-from-surgery.

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