Neuroscience and sexual orientation

Studies have explored structural neural-correlates, functional and/or cognitive relationships, and developmental theories relating to sexual orientation in humans.

[3] As of 2005, sexual dimorphisms in the brain and behavior among vertebrates were accounted for by the influence of gonadal steroidal androgens as demonstrated in animal models over the prior few decades.

[3] This led scientists to look for somatic markers for prenatal hormonal exposure that could be easily, and non-invasively, explored in otherwise endocrinologically normal populations.

Researchers have shown that the SDN-POA aides in sex-dimorphic mating behavior in some mammals, which is representative of human sexual orientation.

[9] The posterior cingulate cortex, a part of the occipital lobe, the region of the brain that processes visual information, has also been demonstrated to have differences based on sexual orientation.

[9] Research has shown that a couple of the areas of connection between the hemispheres of the brain have differences in their size depending on sexual orientation.

Antibodies produced during the immune response are thought to cross the placental barrier and enter the fetal compartment where they bind to the Y-linked molecules and thus alter their role in sexual differentiation, leading some males to be attracted to men as opposed to women.

[10][12] Scientists have estimated that 15–29% of gay men owe their sexual orientation to this effect, but the number may be higher, as prior miscarriages and terminations of male pregnancies may have exposed their mothers to Y-linked antigens.

[11] The few studies which have not observed a correlation between gay men and birth order have generally been criticized for methodological errors and sampling methods.