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.

Callosal Abnormalities Across the Psychosis Dimension: Bipolar Schizophrenia Network on Intermediate Phenotypes

“…The posterior forceps (splenial fibers) interconnect the parietal and occipital cortices, while the anterior splenial fibers interconnect the inferior and medial temporal and posterior cingulate cortices in a bandage- like manner (51) The splenia can be considered a constituent of the hippocampal commissure which carries fibers connecting the hippocampi together with those linking the posterior parietal, medial temporal and medial occipital cortices of the hemispheres (7,52,53). Our observations of reductions in the anterior splenial volume are consistent with previous results from the BSNIP group showing hippocampal and sub-region volume decrements psychosis probands and their relatives across diagnoses (54, 55).…”

“…Small fibers (< 0.4 µm) are more numerous in the genu and anterior splenium interconnecting higher-order prefrontal and temporo-parietal association cortices. The largest fibers in the corpus callosum interconnect the primary auditory cortices (7,8). In healthy brains, the number of callosal fibers is dependent on developmental processes including axon outgrowth, synaptogenesis, and axon pruning (8), and are regulated by genetics (9).…”

White Matter Microstructural Similarity and Diversity of Functional Constipation and Constipation-predominant Irritable Bowel Syndrome

“…The main interhemisphere commissure is required for many aspects of neural function, encompassing inhibition of cortical functions, integration of sensory information, regulation of cognition, processing of emotion, and interhemispheric exchange of information. 52,53 Multiple studies reported CC dysfunction in patients with chronic pain, such as fibromyalgia, 54 migraine, 55 and temporomandibular disorder, 56 supporting the indicative role of the CC in pain perception and pain control. 57 Therefore, we reasoned that aberrations in the WM integrity in the CC may cause the reduction of obstruction to water diffusion and reduced anisotropy, which can be responsible for the perceptional intensity of abdominal discomfort and pain in FC and IBS-C patients.…”

Geometry, landmarks and the cerebral hemispheres: 2D spatial reorientation in split‐brain patients

“…These speculations are in agreement with neuroimaging results, showing the (posterior) hippocampal involvement in geometric processing, as opposed to the (anterior) striatum involvement in landmark encoding (Doeller et al ., ; Hartley et al ., ; Wegman et al ., ). In fact, it has been shown that the splenium connects not only left and right parietooccipital cortex, but together with the hippocampal commissure it connects also the parahippocampal cortex of the left and right hemispheres (Fabri, Pierpaoli, Barbaresi, & Polonara, ; Raybaud, ). To conclude, the present results show that, differently from what happens in other species, the human brain needs at least a partial interhemispheric connection in order to reorient, and we speculate that the hippocampal interhemispheric connections crucially subserve spatial processing.…”