Title: Structural and functional brain rewiring clarifies preserved interhemispheric transfer in humans born without the corpus callosum
Authors: Tovar-Moll F., Monteiro M., Andrade J., Bramati IE., Vianna-Barbosa R., Marins T., Rodrigues E., Dantas N., Behrens TEJ., de Oliveira-Souza R., Moll J., & Lent R.
Journal: Proceedings of the National Academy of Sciences, 111 (21), 7843–7848
Published: 2014
Despite the absence of the major pathway that connects the two hemispheres of the brain, individuals born without the corpus callosum still show some degree of transfer of information between the hemispheres. This finding has perplexed scientists and demonstrates how information is processed in the brain in individuals with ACC is very different to when the corpus callosum has been surgically removed; for example, to alleviate symptoms of severe epilepsy. Following this surgical procedure the classic “disconnection syndrome” is often seen whereby the two hemispheres function independently.
In order to study the nature of this preserved interhemispheric transfer of information in ACC, scientists from D’Or Institute for Research and Education (Rio de Janeiro, Brazil) assessed six individuals with ACC (aged 6 to 33 years) using detailed brain imaging techniques and neuropsychological tests. The individuals with ACC were able to show intact interhemispheric transfer on behavioural measures (e.g., recognising an object by touch without the aid of vision). The brain imaging results showed evidence of functional connectivity between different areas of the brain; that is, some degree of synchrony of activity across brain regions was seen while the individual was resting in the brain scanner. The authors suggest that this connectivity indicates that alternative pathways are formed in the absence of the corpus callosum, which may be compensatory in nature. For example, the bundles of axons normally destined to cross the corpus callosum that become rerouted when the developmental process is interrupted. These white matter bundles (e.g., Probst bundles and sigmoid bundles) still play an important role in connecting brain regions and can explain the cross-transfer of information between hemispheres. The authors conclude by stating that ACC is associated with extensive brain rewiring, and through the plasticity of the brain during prenatal and postnatal development, new circuits are established which allow the integration of information between brain regions.