The anterior commissure
(also known as the precommissure
) is a bundle of nerve fibers (white matter
White matter is one of the two components of the central nervous system and consists mostly of myelinated axons. White matter tissue of the freshly cut brain appears pinkish white to the naked eye because myelin is composed largely of lipid tissue veined with capillaries. Its white color is due to...
), 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
The corpus callosum , also known as the colossal commissure, is a wide, flat bundle of neural fibers beneath the cortex in the eutherian brain at the longitudinal fissure. It connects the left and right cerebral hemispheres and facilitates interhemispheric communication...
, 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.
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 lobe
The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....
s, 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
The ' are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.-...
In a 1991 brain study performed by Laura Allen and Roger Gorski of UCLA observed that there was size differences of the brain's anterior commissure between a group of heterosexual men and a group of women and homosexual men. But as William Brye and Bruce Parson's point out, this study has "many of the same interpretive difficulties as LeVay's." These include a "tremendous" number of exceptions, such as the fact that 27 of 30 homosexual men had anterior commissures that "fell within the range established by 30 heterosexual men." These studies were motivated by the idea that the male homosexual brain is more similar to a female brain in function than the brain of a heterosexual male would be, and hence would express less lateralisation
A longitudinal fissure separates the human brain into two distinct cerebral hemispheres, connected by the corpus callosum. The sides resemble each other and each hemisphere's structure is generally mirrored by the other side. Yet despite the strong anatomical similarities, the functions of each...
and greater cross-talk between hemispheres.