Research has shown that there are structural differences in the brain associated with sexual orientation. While there is no conclusive evidence that environmental or learned effects are responsible for the development of non-heterosexual orientation, many theories concerning the development of sexual orientation involve fetal neural development, with proposed models illustrating prenatal hormone exposure, maternal immunity, and developmental instability. Other proposed factors include genetic control of sexual orientation.
Some key findings from brain imaging studies include:
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Putamen cluster: A study found that homosexual women had a significant effect on the putamen cluster, whereas heterosexual women had increased precentral gyrus GMV. Heterosexual men exhibited more GMV in the thalamus than homosexual men.
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Thalamus: The thalamus of heterosexual individuals was found to be bigger than that of homosexual individuals.
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Suprachiasmatic nucleus: In a sample of brains of homosexual men, an area of the hypothalamus called the suprachiasmatic nucleus (SCN) contains twice as many cells as the SCN of a heterosexual group.
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Cerebral midline structures: A study found that the brains of homosexual men were anatomically different from those of heterosexual men, and that these differences were related to the differences in corresponding measures between heterosexual men and women.
Overall, these findings suggest that sexual orientation is reflected in brain structure characteristics and that these differ between the sexes. However, it is important to note that the causes of homosexuality in the brain are still not fully understood and more research is needed to fully understand the complex interplay of factors that contribute to sexual orientation.
