Direct studies of homosexual brains

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Handedness, finger prints,  and cognitive profiles give us interesting clues about brain organization,  but they only indirectly and weakly support such inferences.  It is, of course,  more difficult to collect the more direct types of relevant information.  One has to pass ethics committees in hospitals to recruit homosexuals and heterosexuals and subject them to magnetic resonance imaging, a procedure which is very expensive.  Unfortunately, the advent of the AIDS virus,  which is now known to often spread to the brain and create pea-sized multiple lesions,  certainly helped to make such research possible,  and has led to some interesting findings.  In addition,  a few very persevering pathologists have been able to collect brains of dead people,  known to have been hetero or homosexual,  to carry out systematic post-mortem examinations,  also leading to interesting results.   Unfortunately though,  this research has,  at the time I put these words to print,  been carried out nearly exclusively on the male sex,  and again the distinction between sexual identity and sexual orientation has usually not been made.    One openly gay neuroscientist named Simon LeVay (1993) found that one of the four interstitial nuclei of the anterior hypothalamus was two to three times smaller in homosexual men and heterosexual women than in heterosexual men,  a finding that had previously been reported by an independent research group (Allen & Gorski, 1991).  Swaab and Hofman (1988) found that the suprachiasmatic nucleus of the hypothalamus was larger in homosexual than heterosexual men.     One research team found that another interstitial nucleus of the hypothalamus is larger in male homosexuals than in male heterosexuals. There is a commissure in the brain linking the two frontal lobes called the anterior commissure.  This structure,  composed of neuron fibers,  has been reported to be larger in male homosexuals and women than in heterosexual men (Allen & Gorski, 1992). Indeed, there is no reason why male homosexual or female brain structures should always be smaller than men's.     The latter type of finding may be particularly important.   It is to be expected that brain systems related to reproductive function could be sex-dimorphic.   So it is not surprising to find several such sex differences in the hypothalamic area.    However,  the anterior commissure has nothing to do, as far as we know,  with the reproductive function.    Sexual identity was not mentioned in any of the reports I have just mentioned,  only sexual orientation.   So this research will need to be replicated with more stringent methodology.  

Enterprising German neurosurgeons lesioned the right hypothalamic ventromedial nucleus of 23 persons,  most of whom were homosexual men.     They claimed to have obtained reversal of sexual orientation in a number of cases.   This procedure raised great controversy in Germany and has now been halted.  As we have just seen, the brain nuclei recently found to be larger in homosexual men than in heterosexual men are the suprachiasmatic and certain interstitial nuclei of the hypothalamus,  not the ventromedial.    So it is not absolutely clear why surgeons would want to destroy the ventromedial nucleus to «reverse» homosexuality rather than the other two nuclei just mentioned  -unless their objective was to destroy a « feminine » nucleus known to be involved in the female sexual response.