| Brain: Anterior commissure | ||
|---|---|---|
| Coronal section of brain through anterior commissure. (Label for "anterior commissure" is on left, third from bottom.) | ||
| The hypophysis cerebri in position. Shown in sagittal section. (Caption for anterior commissure is at center top.) | ||
| Latin | commissura anterior | |
| Gray's | subject #189 840 | |
| NeuroNames | hier-187 | |
| NeuroLex ID | birnlex_1557 | |
The anterior commissure (also known as the precommissure) is a bundle of nerve fibers (white matter), connecting the two 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.
In a sagittal section, the anterior commissure is oval in shape, having a long vertical axis that measures about 5 mm.
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The fibers of the anterior commissure can be traced laterally and posteriorly on either side beneath the corpus 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 amygdala.
In 1992 Laura Allen and Roger Gorski of UCLA measured the anterior commisures of 30 homosexual men, 30 heterosexual men, and 30 heterosexual women. They found that all three groups' commisures were significantly different from one another, with homosexual males having the largest anterior commisure, followed by heterosexual women, and then heterosexual men, who had the smallest anterior commisures. [1]
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. [2] Their assessment is quite deceptive however, as ranges are descriptive statistics rather than inferential statistics and therefore, as their name implies, one cannot draw many inferences from this. All the overlap in ranges indicates is that at least one heterosexual male had an anterior commisure larger than most of the gay males; it says nothing about the overall trend in the data. In fact, this overlap is expected, as humans are highly variable organisms resulting in large ranges and frequent outliers in any research conducted on humans, particularly when separating them based on behavioral characteristics. The statistical tests show with 99% certainty (p < 0.01, so 1% chance that random chance would produce these results) that the averages of the two groups (homosexual males and heterosexual males) are different and therefore they are in fact different populations. Therefore, the existence of a few heterosexual males with exceptionally large anterior commisures for their group does not change the fact that the groups on average were quite different from one another, and that these differences were probably not due to chance.
This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.
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