Disconnection Effects in Split-Brain Patients: A Systematic Evaluation of the Impact of Callosotomy on Cognition and Behavior

Poster Session D - Monday, April 15, 2024, 8:00 – 10:00 am EDT, Sheraton Hall ABC

Selin Bekir¹ (sbekir@ucsb.edu), Tyler Santander¹, Henri Skinner¹, Jessica Simonson¹, Theresa Paul², Lena Hopf⁴, Anna Rada⁴, Friedrich Woermann⁴, Christian Bien⁴, Olaf Sporns³, Barry Giesbrecht¹, Michael Gazzaniga¹, Lukas Volz², Michael Miller¹; ¹University of California Santa Barbara, ²University of Cologne, ³Indiana University, ⁴Bielefeld University, Epilepsy Centre Bethel

How does severing the cerebral hemispheres impact cognition and behavior in ‘split-brain’ patients,who undergo callosal sectioning for intractable epilepsy? A sharp contrast exists between clinical neurology and experimental psychology in their perspectives on callosotomy’s impact.Initial clinical assessments indicated minimal cognitive changes, while subsequent experiments using lateralized testing revealed significant 'disconnection effects'-indicating independent information processing by each hemisphere without the other's awareness or involvement.The ongoing debate about the exact nature of these effects persists due to variations in stimuli, task complexity, post-surgery timing, and callosotomy extent. Addressing this knowledge gap would advance our understanding of information propagation and integration across long-range brain networks, illuminating their role in cognition. In our project, we employed an array of lateralized tests across different cognitive domains/modalities (sensory-motor, sensory-tactile, spatial, visual). Participants performed in both crossed-uncrossed trials (e.g.,left visual field stimuli requiring either a crossed right-hand response or an uncrossed left-hand response) and cross-matching trials involving simultaneous stimuli presentation to both hemispheres for same/different judgments. Preliminary results from 5 callosotomy (2 partial, 3 full) patients show that, full-callosotomy led to significant performance disruptions in crossed but not in uncrossed trials. Hemispheric dominances for speech(left hemisphere) and visuospatial processing(right hemisphere) were supported. Performance in non-dominant hemisphere in speech production and visuospatial tasks broke down following callosotomy. No disconnection effects were observed in partial split-brain patients, even though one of them only had ~1 cm splenium intact, suggesting a threshold-like effect. Our study provides insights into the interhemispheric information integration in cognition and in human agency and consciousness.

Topic Area: PERCEPTION & ACTION: Multisensory