Anterior commissure

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Anterior commissure

"Spinothalamic Tract 3.23.21" by?aandp

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Coronal?cross-section of brain showing the?anterior commissure. (left, third from bottom.)

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Tractography of anterior commissure

Details

Identifiers

Latin

commissura anterior

NeuroNames

205,?390

NeuroLex?ID

birnlex_1557

TA98

A14.1.08.421

TA2

5613

FMA

61961

Anatomical terms of neuroanatomy

[edit on Wikidata]

The?anterior commissure?(also known as the?precommissure) is a?white matter?tract?(a bundle of?axons) 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.

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?to link the two cerebral hemispheres of the brain and also interconnects the?amygdalae?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.

Contents

·?1Structure

·?2Function

·?2.1Sexuality

·?3Gallery

·?4See also

·?5References

·?6External links

Structure[edit]

The fibers of the anterior commissure can be traced laterally and posteriorly on either side beneath the?striatum?into the substance of the temporal lobe.

It serves in this way to connect the two?temporal lobes, but it also contains?decussating fibers?from the?olfactory tracts, and is a part of the?neospinothalamic tract?for pain. The anterior commissure also serves to connect the two?amygdalae.

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,[1][2]?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).[3]

Function[edit]

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Averaged tracking results of ten normal controls showing the Anterior Commissure. Image from Winter and Franz (2014)[4]

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).[5]?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).[4]

Sexuality[edit]

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(?????).[6]

（或許與ACh system控制下的basolateral amygdala--nucleus accumbens circuit有關，即與瞬時“小爆發(fā)”行為有關。通過anterior commissure，兩側的basolateral?amygdala相互有聯(lián)系，語言記憶本身位于temporal lobe，語言對應的事物記憶本尊在prefrontal cortex, 而一種很重要的記憶模式就是通過皮層與皮層間聯(lián)系構建，尤其兩個prefrontal cortex間聯(lián)系，這樣一來，通過ACh system的遞質在neocortex處瞬間同時爆發(fā)，使得兩側的basolateral?amygdala都接收到了來自neocortex的信息，兩側的nucleus?accumbens都被瞬間激發(fā)，從而產生典型的“小爆發(fā)”行為。這樣的行為狀態(tài)決定了兩側大腦的一定同步性，不存在一側大腦監(jiān)視控制另一側大腦的情況，因此可以明顯區(qū)別于其他行為模式。）

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.[7]?However, because range is defined only by the two most extreme data points in a group,[8]?the existence of a single heteroSexual male with an exceptionally large anterior commissure for his group (an outlier[9]) 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.[6]

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.[10]

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.[11]