Full interhemispheric integration sustained by a fraction of posterior callosal fibers
- Tyler Santander
- Selin Bekir
- Theresa Paul
- Jessica M. Simonson
- Valerie M. Wiemer
- Henri Etel Skinner
- Johanna L. Hopf
- Anna Rada
- Friedrich G. Woermann
- Thilo Kalbhenn
- Barry Giesbrecht
- Christian G. Bien
- Olaf Sporns
- Michael S. Gazzaniga
- Lukas J. Volz
- Michael B. Miller
2025-10-21
The dynamic integration of the lateralized and specialized capacities of the two cerebral hemispheres constitutes a hallmark feature of human brain function. This interhemispheric exchange of information critically depends upon the corpus callosum. Classical anatomical descriptions of callosal organization outline a topographic gradient from front to back, such that specific transcallosal fibers support distinct aspects of integrated brain function. Here, we present a challenge to this conventional model. Using neuroimaging data obtained from a new cohort of adult corpus callosotomy patients, we leverage modern network neuroscience techniques to show that full interhemispheric integration can be achieved via a small proportion of posterior callosal fibers. Partial callosotomy patients with spared callosal fibers retained widespread patterns of interhemispheric functional connectivity and showed no signs of behavioral disconnection, even with only 1 cm of the splenium intact. Conversely, only complete callosotomy patients demonstrated sweeping disruptions of interhemispheric network architectures, aligning with disconnection syndromes long-thought to reflect diminished information propagation and communication across the brain. These findings motivate an evolving mechanistic understanding of synchronized interhemispheric neural activity for large-scale human brain function and behavior.