Suprachiasmatic Nucleus - Sexual Orientation and The SCN

Sexual Orientation and The SCN

In 1990, Professor D.F. Swaab carried out research into this part of hypothalamus searching for an organic basis for homosexuality in humans. He found the suprachiasmatic nucleus to be nearly twice the size in homosexual men as heterosexual men. This research was further confirmed by Laura S. Allen, who found the midsagittal plane of the anterior commissure of the hypothalamus to be one third larger in male homosexual subjects than in male heterosexuals.

Professor Swaab conducted a follow-on study in rats. Male rats were treated with ATD, an aromatase inhibitor, which prevents testosterone from converting to estradiol. The experiment compared three different populations, an untreated control group, a prenatally treated group, and a pre- and postnatally treated group. Adult rats that were treated with ATD prenatally showed no difference from the control group. Adult rats treated with ATD both pre- and postnatally, however, had significantly more neurons in the SCN than the controls. These male rats also exhibited bisexual behavior. According to the authors, "This observation supports the hypothesis that the increased number of vasopressin neurons found earlier in the SCN of adult homosexual men might reflect differences that took place in the interaction between sex hormones and the brain early in development."

However, Swaab's research was "criticized on both methodological and conceptual grounds" in a 2003 review by Karori Mbugua. Among the issues Mbugua raises are: 1. sexual orientation was assessed by health care professionals by unknown means, rather than being self-reported. 2. While subjects "died of opportunistic infections resulting from AIDS, they were not matched for clinical diagnosis". Thus the diseases which actually killed the subjects were not controlled for.