Functional topography of the corpus callosum investigated by DTI and fMRI

Abstract

This short review examines the most recent functional studies of the topographic organization of the human corpus callosum, the main interhemispheric commissure. After a brief description of its anatomy, development, microstructure, and function, it examines and discusses the latest findings obtained using diffusion tensor imaging (DTI) and tractography (DTT) and functional magnetic resonance imaging (fMRI), three recently developed imaging techniques that have significantly expanded and refined our knowledge of the commissure. While DTI and DTT have been providing insights into its microstructure, integrity and level of myelination, fMRI has been the key technique in documenting the activation of white matter fibers, particularly in the corpus callosum. By combining DTT and fMRI it has been possible to describe the trajectory of the callosal fibers interconnecting the primary olfactory, gustatory, motor, somatic sensory, auditory and visual cortices at sites where the activation elicited by peripheral stimulation was detected by fMRI. These studies have demonstrated the presence of callosal fiber tracts that cross the commissure at the level of the genu, body, and splenium, at sites showing fMRI activation. Altogether such findings lend further support to the notion that the corpus callosum displays a functional topographic organization that can be explored with fMRI.

Keywords: Corpus callosum, Interhemispheric transfer, Functional magnetic resonance imaging and diffusion tensor imaging, Brain imaging, Topographic organization

Core tip: A combined approach using diffusion tensor imaging and tractography, two recently developed imaging techniques, and functional magnetic resonance imaging (fMRI) has enabled detection of fMRI activation evoked by specific sensory or motor tasks in the corpus callosum, and reconstruction of the trajectory of the commissural fibers interconnecting primary cortical areas activated by the same tasks. These findings confirm that the corpus callosum has a functional topographic organization and that fMRI may be used to explore it.