The INAH 3 is the third interstitial nucleus of the anterior hypothalamus. The INAH has been implicated in sexual behavior because of known sexual dimorphism in this area in humans and because it corresponds to an area of the hypothalamus that when lesioned, impairs heterosexual behavior in non-human primates without affecting sex drive. It has been reported to be smaller on average in homosexual men than in heterosexual men, and in fact has approximately the same size as INAH 3 in heterosexual women.

A scientific paper authored by Simon LeVay and published in the prominent journal Science suggests that the region is an important biological substrate with regards to sexual orientation. ^[1][2]

References

1. ↑ "Central Nervous System Dimorphisms Related to Reproductive Behaviors" Dale Purves ed., Neuroscience, 2:ed (2001) Online http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=neurosci.section.2127
2. ↑ LeVay S 1991 A difference in hypothalamic structure between heterosexual and homosexual men. Science 253: 1034?7