The Corpus Callosum and Brain Hemisphere Communication; How does the corpus callosum mediate interhemispheric transfer
Knaap, L.J. van der
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The corpus callosum is the largest white matter structure in the human brain, connecting symmetrical and asymmetrical cortical regions of the opposing cerebral hemispheres. Complete and partial callosotomies and callosal lesion studies have provided a great opportunity to further investigate the organization and connection of motor and sensory functions across hemispheres as well as cortical representations of cognitive functions and perceptual processes and the lateralization of function. It has also granted more insight into the function of the corpus callosum, namely the facilitation of communication between the cerebral hemispheres. The corpus callosum is thought to have attributed to the functional specialization of hemispheres by mediating information transfer between hemispheres, but how the corpus callosum mediates this transfer is still a topic of debate. Some pose that the corpus callosum maintains independent processing between the two hemispheres, causing a greater connectivity to increase laterality effects. Others say that the corpus callosum shares information between hemispheres and serves an excitatory function, causing greater connectivity to decrease laterality effects. These theories are further explored by reviewing recent behavioural studies and morphological findings to tell us more about callosal function. Additional information regarding callosal function in relation to altered morphology and dysfunction in disorders is also reviewed to supplement the knowledge of callosal involvement in interhemispheric transfer. Both the excitatory as well as the inhibitory theory seem likely candidates to describe callosal function, although evidence from recent studies favour the inhibitory model. However the corpus callosum is a complex structure consisting of distinct components which could allow for the possibility to have both an excitatory or inhibitory function that can alter according to task demands. Instead of focusing on the corpus callosum as a single structure it would be beneficial for future research to investigate the functional role of the callosal sub regions, and use better methods to determine functional connectivity when looking at interhemispheric transfer.