# No disconnection syndrome after near-complete callosotomy

## TL;DR

This study shows that even a small part of the corpus callosum can maintain brain integration, preventing disconnection syndromes after surgery.

## Contribution

The study reveals that minimal callosal remnants can support full functional unity, challenging existing anatomical models.

## Key findings

- Complete callosotomy leads to disconnection syndromes across all tested domains.
- A patient with only the splenium retained showed no disconnection syndrome.
- Minimal callosal remnants enable integrated behavior, suggesting brain reorganization.

## Abstract

Sensorimotor processing in the human brain is largely lateralized, with the corpus callosum integrating these processes into a unified experience. Following complete callosotomy, this integration breaks down, resulting in disconnection syndromes. We asked how much of the corpus callosum is sufficient to support functional unity—the absence of disconnection syndrome—by comparing three complete callosotomy patients with one retaining only the splenium. Using lateralized tasks across visual, tactile, visuospatial, and language domains, we predicted domain-specific deficits in the splenium-only patient based on established anatomical models of callosal topography. Strikingly, while complete callosotomy patients exhibited disconnection syndromes, the splenium patient demonstrated functional unity across all domains—as if his entire corpus callosum were intact. Our findings highlight the brain’s remarkable capacity to maintain behavioral integration through minimal preserved pathways, highlighting how the structure-dependent reorganizational capacity of the human brain may allow to preserve functional unity.

A battery of bedside tests was designed to test split-brain patients across multiple functional domains. While full callosotomy introduced disconnection syndromes across all domains, even minimal callosal remnants enabled fully integrated behavior.