An extrinsic subcortical fiber bundle that runs between the medial amygdala (in the temporal lobe and various regions in the forebrain (the frontal lobe) including the medialpreoptic area, mainly to the anterior hypothalamus. It is located along the medial border of the caudate nucleus. Considered part of the extended amygdala. It carries "outputs" from the amygdala, transmitting them to the hypothalamus, and the preoptic are of the cortex. (Huh? It's a small bundle of nerves that carry nerve signals from one area of the brain to another.)

Where the stria terminalis connects to the hypothalamus is known as the bed nucleus of the stria terminalis (BST or BNST).

Some signals traveling through the brain in regards to sexual function travel through this area of the brain. For example, stimulation of a certain section of the amygdala was shown to cause ovulation in the female - this ceased if the stria terminalis was cut.

Also, the BST may be involved in the brain's formation and or transmission of emotions of fear and anxiety. Some studies have been done involving intentional bruising and damaging of the BST, and creating negative experiences for the subject. Those with a damaged BST seemed to react more strongly to the negative experiences.

The BST may even play a role in drug addiction, at least to some substances. Research on animals involving addictions to heroin and cocaine have shown involvement, as injections have been administered directly to the BST, avoiding the amygdala completely. These injections have resulted in an increase or decrease in desire for the drug, depending on the substance injected.

The stria terminalis, especially the bed nucleus, has been shown to have significant differences in size and density between men and women, especially the central subdivision of the BST, known as the BSTc. (Yes, this is a very tiny part of the brain, sizewise.) The BSTc is, on average, 44 percent larger in men than in women.

The apparent sex differences in the BST and BSTc may also be linked to a biological indicator of transsexuality. Studies done on the brains of deceased transsexuals have shown the BSTc to be in the same size range as the gender the person felt they were, instead of matching the sex of the genitalia. While the sample sizes were quite low (apparently there is difficulty finding enough people to examine), the study did cover other explanations, showing that hormone treatment was not a factor. A neurobiologist, Dick Swaab, states, "We know from animal experiments that in adulthood you cannot change the size of the nucleus using sex hormones. You can do that only in development."

Sources:
The Penguin Dictionary of Psychology, by Arthur S. Reber
Glossary of Neuroanatomical and Neurological Terms, http://www.umanitoba.ca/faculties/medicine/anatomy/neuro/gloss/s.htm
The Amygdala and the Emotions, http://www.benbest.com/science/anatmind/anatmd9.html
"Transsexual Brains", Josie Glausiusz, Discover Magazine, January 1996

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