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Commissural Pathways 

Commissural Pathways
Commissural Pathways

Marco Catani

and Michel Thiebaut de Schotten

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date: 22 October 2019

Commissural pathways are composed of fibres connecting broadly similar regions in the two cerebral hemispheres. In the human brain they consist of the anterior commissure, corpus callosum, and the hippocampal commissure of the fornix. These three commissures can be easily visualized with current tractography methods (Figure 9.1; for the hippocampal commissure see Figure 11.2 in Chapter 11).

Other small commissures are composed of short fibres connecting adjacent paramedian structures of the thalamus (massa intermedia), the tegmentum (tectal commissure of Forel), the habenula (habenular commissure), and the brainstem (reticular commissure). A general assumption underlying the concept of commissural connections is that the information is transferred between homologous cortical or subcortical regions. There are, however, a significant number of heterotopic commissural fibres connecting non-homologous regions, at least in the corpus callosum (Clarke, 2003). Furthermore, the communication between the two sides can also occur through non-commissural tracts, such as the superior cerebellar peduncle fibres that connect the deep cerebellar nuclei of one side with the thalamic nuclei of the contralateral side. The commissural pathways play a significant role in the development of interhemispheric specialization and integration of several motor, perceptual, and cognitive functions (Gazzaniga, 2000). The anterior commissure and corpus callosum will be described in this chapter, while the hippocampal is dealt separately in Chapter 11.

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