No Disconnection Syndrome after Near-Complete Callosotomy

Abstract

Much of the sensory-motor processing in the human brain is lateralized to either hemisphere, with the corpus callosum integrating these distinct processes into a seemingly unified conscious experience. The corpus callosum is thought to be topographically organized, with different subregions along its anterior-to-posterior axis involved in integrating information across different sensory modalities and cognitive domains. In complete callosotomy patients, where the corpus callosum is fully severed, this integration is typically disrupted across these domains. But which types of inter-hemispheric integration can still be preserved with small posterior callosal remnants? We studied four callosotomy patients—three complete and one partial with approximately 1 cm of preserved splenium—using an array of lateralized visual, tactile, visuospatial, and language tasks. While complete callosotomy patients showed the expected behavioral disconnection effects—performing poorly on tasks requiring inter-hemispheric integration but well on intra-hemispheric ones—the partial callosotomy patient with a preserved portion of the splenium showed no disconnection effects across all tasks. The splenium is traditionally implicated in visual transfer, yet our findings show that minimal splenial preservation maintains functional integration across multiple perceptual and cognitive domains. This is at odds with the presumed topographical organization of the corpus callosum, suggesting a broader inter-hemispheric integrative capacity of the posterior callosal fibers. Structure-function relationships in brain networks are known to be complex and nonlinear— these findings provide novel insights into flexible structural mechanisms for inter-hemispheric communication enabling a variety of integrated behaviors.

The copyright holder for this preprint is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY-NC-ND 4.0 International license.