Comments on the Neuroanatomy of Human Sexual Orientation and Proposed Neuroendocrine Hypotheses

Qazi Rahman

Published: 26 October 1999

Sex differences in neuroanatomy, although controversial, have been widely reported in a number of neural substrates. Such functional sex differences are probably due to the organizing effects of gonadal steroids in utero. These data have permitted the investigation of within-sex neuroanatomical differences between homosexuals and heterosexuals. Evidence is reviewed which demonstrate neuroanatomical dimorphisms between homosexual and heterosexual males in the supra-chiasmatic nucleus (SCN), the interstitial nuclei of the anterior hypothalamus (INAH), and the anterior commisure (AC). The paucity of neuroanatomical data for homosexual females is acknowledged. The available evidence is taken to support a proposed model implicating sex-atypical neuroendocrine differentiation as a causative mechanism in developing variations in sexual orientation. The role of alternative, causative developmental processes is also acknowledged.

Keywords: neuroanatomical dimorphisms, neuroendocrine differentiation, homosexual, heterosexual, sex differences