The anterior commissure (also known as the precommissure) is a

white matter White matter refers to areas of the central nervous system that are mainly made up of myelinated axons, also called Nerve tract, tracts. Long thought to be passive tissue, white matter affects learning and brain functions, modulating the distr ...

tract (a bundle of

axon An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences) is a long, slender cellular extensions, projection of a nerve cell, or neuron, ...

s) connecting the two

temporal lobe The temporal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain. The temporal lobe is involved in pr ...

s of the

cerebral hemisphere The vertebrate cerebrum (brain) is formed by two cerebral hemispheres that are separated by a groove, the longitudinal fissure. The brain can thus be described as being divided into left and right cerebral hemispheres. Each of these hemispheres ...

s across the midline, and placed in front of the columns of the fornix. In all but five species of mammal the great majority of fibers connecting the two hemispheres travel through the corpus callosum, which in humans and all non- monotremes is more than 10 times larger than the anterior commissure. 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. The anterior commissure plays a key role in pain sensation, more specifically sharp, acute pain. It also contains decussating fibers from the olfactory tracts, vital for the sense of smell and chemoreception. The anterior commissure works with the

posterior commissure The posterior commissure (also known as the epithalamic commissure) is a rounded band of white fibers crossing the middle line on the dorsal aspect of the rostral end of the cerebral aqueduct. It is important in the bilateral pupillary light re ...

to link the two cerebral hemispheres of the brain and also interconnects the

amygdala The amygdala (; : amygdalae or amygdalas; also '; Latin from Greek language, Greek, , ', 'almond', 'tonsil') is a paired nucleus (neuroanatomy), nuclear complex present in the Cerebral hemisphere, cerebral hemispheres of vertebrates. It is c ...

e and temporal lobes, contributing to the role of memory, emotion, speech and hearing. It also is involved in olfaction, instinct, and sexual behavior. In a sagittal section, the anterior commissure is oval in shape, having a long vertical axis that measures about 5 mm.

Structure

It interconnects multiple cortical regions of the

s, the amygdalae, and

olfactory bulbs The olfactory bulb (Latin: ''bulbus olfactorius'') is a grey matter, neural structure of the vertebrate forebrain involved in olfaction, the sense of odor, smell. It sends olfactory information to be further processed in the amygdala, the orbitof ...

. It is a part of the neospinothalamic tract for pain.

Function

The functionality of the anterior commissure is still not completely understood. Researchers have implicated it in functions ranging from colour perception to attention. One such study supported colour perception in callosal agenesis (those born without a corpus callosum; Barr & Corballis, 2002). Other studies have built on this to imply that the anterior commissure can be a compensatory pathway in those without a corpus callosum, presenting diffusion tensor imaging (DTI) techniques to better elucidate the anterior commissure and how it might be implicated in various functions (Winter & Franz, 2014).

Sexuality

In 1992, Laura Allen and Roger Gorski of UCLA measured the anterior commissures of 30 homosexual men, 30 heterosexual men, and 30 heterosexual women. They found that all three groups' commissures were significantly different from one another, with homosexual males having the largest anterior commissure, followed by heterosexual women, and then heterosexual men, who had the smallest anterior commissures. In 1993, a review by Byne and Parsons criticized this research, noting that 27 of the 33 homosexual males fell within the range of heterosexual males in the study. However, because range is defined only by the two most extreme data points in a group, the existence of a single heterosexual male with an exceptionally large anterior commissure for his group (an outlier) would cause this large range irrespective of the data from the rest of the individuals in the group. This individual's existence would not change the fact that the groups on average were quite different from one another, and that these differences were statistically significant. A later report by Byne et al. (2001) noted that

We also measured the anterior commissure in the same blocks of tissue used for the present hypothalamic study (data not shown) and were unable to replicate a report (by Allen and Gorski) that its cross-sectional area is larger in women than in men.

Also, a study by Lasco et al. (2002) said:

We examined the cross-sectional area of the AC in postmortem material from 120 individuals, and found no variation in the size of the AC with age, HIV status, sex, or sexual orientation.

Other animals

The corpus callosum allows for communication between the two hemispheres and is found only in placental mammals (the eutherians), while it is absent in monotremes and marsupials, as well as other vertebrates such as birds, reptiles, amphibians and fish. The anterior commissure serves as the primary mode of interhemispheric communication in marsupials, and which carries all the commissural fibers arising from the

neocortex The neocortex, also called the neopallium, isocortex, or the six-layered cortex, is a set of layers of the mammalian cerebral cortex involved in higher-order brain functions such as sensory perception, cognition, generation of motor commands, ...

(also known as the neopallium), whereas in placental mammals the anterior commissure carries only some of these fibers).Butler, Ann B., and William Hodos (2005). Comparative Vertebrate Neuroanatomy: Evolution and Adaptation, p. 361

Gallery

File:Slide12qq.JPG, Anterior commissure

References

External links

Overview
at

University of Cambridge The University of Cambridge is a Public university, public collegiate university, collegiate research university in Cambridge, England. Founded in 1209, the University of Cambridge is the List of oldest universities in continuous operation, wo ...

* * https://web.archive.org/web/20070512234725/http://www2.umdnj.edu/~neuro/studyaid/Practical2000/Q09.htm *
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