Commissural fibers

Commissural fiber
Coronal cross-section of brain showing the corpus callosum at top and the anterior commissure below
Details
Identifiers
Latin	fibra commissuralis, fibrae commissurales telencephali
NeuroNames	ancil-221
Dorlands /Elsevier	f_05/12361896
TA	A14.1.00.017 A14.1.09.569
FMA	75249
Anatomical terms of neuroanatomy []

The commissural fibers or transverse fibers are white-matter structures that connect the two hemispheres of the brain. In contrast to commissural fibers, association fibers connect regions within the same hemisphere of the brain, and projection fibers connect each region to other parts of the brain or to the spinal cord.

The commissural fibers include:

The corpus callosum is the largest commissural fiber system in the human brain. It consists of about 200-300 million axons that connect the two cerebral hemispheres. The corpus callosum is essential to the communication between the two hemispheres.

A recent study of individuals with agenesis of the corpus callosum suggests that the corpus callosum plays a vital role in problem solving strategies, verbal processing speed, and executive performance. Specifically, the absence of a fully developed corpus callosum is shown to have a significant relationship with impaired verbal processing speed and problem solving.

Another study of individuals with multiple sclerosis provides evidence that structural and microstructural abnormalities of the corpus callosum are related to cognitive dysfunction. Particularly, verbal and visual memory, information processing speed, and executive tasks were shown to be impaired when compared to healthy individuals. Physical disabilities in multiple sclerosis patients also seem to be related to abnormalities of the corpus callosum, but not to the same extent of other cognitive functions.

Using diffusion tensor imaging, researchers have been able to produce a visualization of this network of fibers, which shows the corpus callosum has an anteroposterior topographical organization that is uniform with the cerebral cortex.

The anterior commissure (also known as the precommissure) is a bundle of nerve fibers (white matter), connecting the two temporal lobes of the cerebral hemispheres across the midline, and placed in front of the columns of the fornix. The great majority of fibers connecting the two hemispheres travel through the corpus callosum, which is over 10 times larger than the anterior commissure, and other routes of communication pass through the hippocampal commissure or, indirectly, via subcortical connections. Nevertheless, the anterior commissure is a significant pathway that can be clearly distinguished in the brains of all mammals.