Commissural fiber

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Commissural fiber
Coronal cross-section of brain showing the corpus callosum at top and the anterior commissure below
Details
Identifiers
Latinfibra commissuralis, fibrae commissurales telencephali
NeuroNames1220
TA98A14.1.00.017
A14.1.09.569
TA25603
FMA75249
Anatomical terms of neuroanatomy

The commissural fibers or transverse fibers are

projection fibers connect each region to other parts of the brain or to the spinal cord.[1]

Structure

The commissural fibers make up tracts that include the corpus callosum, the anterior commissure, and the posterior commissure.

Corpus callosum

Main article: Corpus callosum

The corpus callosum is the largest commissural tract 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.[2]

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.[3]

Another study of individuals with

cognitive functions.[4]

Using

anteroposterior topographical organization that is uniform with the cerebral cortex
.

Anterior commissure

Main article: Anterior commissure

The anterior commissure (also known as the precommissure) is a tract that connects the two temporal lobes of the cerebral hemispheres across the midline, and placed in front of the columns of 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.

Using diffusion tensor imaging, researchers were able to approximate the location of the anterior commissure where it crosses the midline of the brain. This tract can be observed to be in the shape of a bicycle as it branches through various areas of the brain. Through diffusion tensor imaging results, the anterior commissure was categorized into two fiber systems: 1) the olfactory fibers and 2) the non-olfactory fibers.[5]

Posterior commissure

Main article: Posterior commissure

The posterior commissure (also known as the epithalamic commissure) is a rounded nerve tract crossing the middle line on the dorsal aspect of the upper end of the cerebral aqueduct. It is important in the bilateral pupillary light reflex.

Evidence suggests the posterior commissure is a tract that plays a role in language processing between the right and left hemispheres of the brain. It connects the pretectal nuclei. A case study described recently in The

alexia without agraphia. It is evident from this case study of alexia without agraphia that the posterior commissure plays a vital role in transferring information from the right occipital cortex to the language centers of the left hemisphere.[6]

Other

The

hippocampal commissure
.

Function

Aging

Age-related decline in the commissural fiber tracts that make up the corpus callosum indicate the corpus callosum is involved in memory and executive function. Specifically, the posterior fibers of the corpus callosum are associated with episodic memory. Perceptual processing decline is also related to diminished integrity of occipital fibers of the corpus callosum. Evidence suggests that the

genu of the corpus callosum does not contribute significantly to any one cognitive domain in the elderly. As fiber tract connectivity in the corpus callosum declines due to aging, compensatory mechanisms are found in other areas of the corpus callosum and frontal lobe. These compensatory mechanisms, increasing connectivity in other parts of the brain, may explain why elderly individuals still display executive function as a decline of connectivity is seen in regions of the corpus callosum.[7]

Older adults compared to younger adults show poorer performance in balance exercises and tests. A decline in white matter integrity of the corpus callosum in older individuals may explain declines in the ability to balance. Changes in the white matter integrity of the corpus callosum may also be related to cognitive and motor function decline as well. Decreased white matter integrity effects proper transmission and processing of sensorimotor information. White matter degeneration of the

genu of the corpus callosum is also associated with gait, balance impairment, and the quality of postural control.[8]

Other animals

The

placental mammals. The anterior commissure serves as the primary mode of interhemispheric communication in marsupials,[9][10] and which carries all the commissural fibers arising from the neocortex (also known as the neopallium), whereas in placental mammals the anterior commissure carries only some of these fibers).[11]

References

Public domain This article incorporates text in the public domain from page 843 of the 20th edition of Gray's Anatomy (1918)

  1. ISBN 9780443071683
    . The nerve fibres which make up the white matter of the cerebral hemispheres are categorized on the basis of their course and connections. They are association fibres, which link different cortical areas in the same hemisphere; commissural fibres, which link corresponding cortical areas in the two hemispheres; or projection fibres, which connect the cerebral cortex with the corpus striatum, diencephalon, brain stem and the spinal cord.
  2. ^ Kollias, S. (2012). Insights into the Connectivity of the Human Brain Using DTI. Nepalese Journal of Radiology, 1(1), 78-91.
  3. ^ Hinkley LBN, Marco EJ, Findlay AM, Honma S, Jeremy RJ, et al. (2012) The Role of Corpus Callosum Development in Functional Connectivity and Cognitive Processing. PLoS ONE 7(8): e39804. doi:10.1371/journal.pone.0039804
  4. ^ Llufriu S, Blanco Y, Martinez-Heras E, Casanova-Molla J, Gabilondo I, et al. (2012) Influence of Corpus Callosum Damage on Cognition and Physical Disability in Multiple Sclerosis: A Multimodal Study. PLoS ONE 7(5): e37167. doi:10.1371/journal.pone.0037167
  5. ^ Kollias, S. (2012). Insights into the Connectivity of the Human Brain Using DTI. Nepalese Journal of Radiology, 1(1), 78-91.
  6. ^ Mulroy, E., Murphy, S., & Lynch, T. (2012). Alexia without Agraphia. Instructions for Authors, 105(7).
  7. ^ Voineskos, A. N., Rajji, T. K., Lobaugh, N. J., Miranda, D., Shenton, M. E., Kennedy, J. L., ... & Mulsant, B. H. (2012). Age-related decline in white matter tract integrity and cognitive performance: A DTI tractography and structural equation modeling study. Neurobiology of aging, 33(1), 21-34.
  8. ^ Bennett, I. J. (2012). Aging, implicit sequence learning, and white matter integrity.
  9. ^ Ashwell, Ken (2010). The Neurobiology of Australian Marsupials: Brain Evolution in the Other Mammalian Radiation, p. 50
  10. ^ Armati, Patricia J., Chris R. Dickman, and Ian D. Hume (2006). Marsupials, p. 175
  11. ^ Butler, Ann B., and William Hodos (2005). Comparative Vertebrate Neuroanatomy: Evolution and Adaptation, p. 361

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