Neuropsychological study of homosexuals

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 In my opinion, there are indeed brain differences between homosexual men and heterosexual men,  and I would go so far as to say that some of these differences are probably direct and sufficient causes of homosexuality.  This does not mean, of course, that there do not exist purely culturally determined trajectories toward homosexuality.  Biologically determination of homosexuality or heterosexuality consists of long cascades of events starting during the second trimester of fetal life.    Along the way,  before birth,  the brain either gets masculinized, or remains feminized.  In most people,  the brain gets completely masculinized before birth or remains feminine.  Milton Diamond reported a case who was accidentally castrated during circumcision at age 7 mo. The decision was then made at age 17 months to rear the adolescent as a girl. While many researchers at the time insisted that this case proved that sex differences were not genetic, the author maintained that there exist different male and female nervous systems. In fact, the adolescent showed great ambivalence about her sexuality and her adjustment as a woman, thus supporting the author's original contention.  A case reported recently in a medical journal brings support to this point of view.  A male newborn in the United States was a victim 15 years ago of a surgical error.   His penis was accidentally severed. The medical staff and parents secretly opted for raising the child as a girl.   She received corrective surgery and the requisite hormonal treatment.   She was not informed of this and thought she was a girl.  Among several interesting anecdotes reported by the authors of the scientific article, the following is particularly intriguing:  she had always insisted on urinating standing up  [this could well be an artifact:  in most human cultures throughout history,  it seems that the two sexes have urinated in the same manner,  standing, squatting, or on all fours !  Unbelievable as this may seem to westerners such as myself,  data to this effect has been presented by Frank Beach in a chapter he published in 1987.  At age fourteen,  her parents explained to her what had happened.  She immediately insisted on becoming a boy  (undergoing a sex change operation) because,  as she stated,  she had long since felt like one.   This interesting case has been reported in a scientific journal,  but several readers may prefer to look up a popularized account in one of the early 1997 issues of Time Magazine.   A second similar case has just recently been reported by Bradley and colleagues.   At seven months, a boy’s circumcision went wrong,  the penis and testicles were removed,  and the boy raised as a girl.  As an adult this person developed a bisexual identity and a bisexual orientation.

In about 12% of the male population the brain has been incompletely masculinized (homosexuality, transsexualism).   Now before I review what is known about the brains of homosexuals,  I must give two caveats.  First, few research neuropsychologists interested in sexual orientation have actually distinguished sexual orientation and sexual identity.   This has been a most unfortunate oversight.  It turns out that neuropsychologically speaking,  the two conditions seem quite different.   Much of what I will have to say about homosexuals' brains is unfortunately based on studies which included as subjects unoperated transsexuals as well as homosexuals and bisexuals -without having made any attempt to distinguish them.  Second,  most of the neuropsychological and neurobiological research on homosexuality has been done on men.   I suspect this has been so because male homosexuality is more prevalent, and thus subjects are easier to recruit.  Also,  perhaps, the proportion of gay men who are willing to disclose their sexual orientation could be higher than is the case for lesbians,  although I don’t think this is very likely.  Finally,  research on homosexuality often fits into larger research protocols on the AIDS virus,  a virus which up until now has threatened gays more than lesbians. 

There have been several studies of handedness and sexual orientation.   Initial findings of more left handedness in gay men (Lindesay, 1987) have not been replicated (Satz, Miller, Selnes et Van-Gorp, 1991),  -even though the finding has indeed been extended to lesbians (McCormick, Witelson et Kingstone, 1990).  The latter finding is particularly surprising and should certainly be replicated.  A particularly well designed recent study found that male-to-female transsexuals are more often left handed,  but not homosexual men without gender dysphoria (transsexualism). Ellis and Peckham  (1991) found that male but not female offspring of stressed mothers were more often left handed  -a finding that fits with the Dörner model as well as Lindesay’s finding.  One research team has also found that masculinized congenital hyperplasia girls are slightly more often left handed than their endocrinologically normal sisters.   One intriguing recent finding, by Jeff Hall and Doreen Kimura (1993), is of a special asymmetry of finger prints in homosexual men, suggesting that there are very early prenatal factors in the determination of homosexuality,  since finger ridges appear early in fetal life.   This isolated finding was not given too much credence until replicated. The Feb 8 issue of the Sunday Times (of London) carried an article describing a new fingerprint study, this time by Richard Green.  The study seems to precisely replicate,  but this time with a gigantic sample of 300 homosexual men, the earlier study by Hall and Kimura. As with the earlier study, there is unfortunately no comparison of lesbians versus heterosexual women.  

There has been a flurry of studies designed to determine whether homosexual men have cognitive profiles suggestive of atypical cortical asymmetry and hemispheric specialization.  The results are quite mixed,  but overall they suggest that male homosexual cognitive profiles are not organized exactly like those of male heterosexuals. McCormick and Witelson (1991) and Hall and Kimura (1995) found that homosexual men have a cognitive profile resembling normal women (high verbal fluency,  low visuospatial skill) –but there were no differences between homosexuals and heterosexuals on dichotic listening nor in prevalence of sinistrality in the first of these studies.  So if anything,  male homosexual brain organization (responsible for cognitive operations) tends slightly in the direction of that of normal women.  Dr Wegesin at Columbia University, College of Physicians and Surgeons, recently  reported results confirming this general trend.  Heterosexual (HT) women, HT men, lesbians, and gay men (20 per group) completed a lexical-decision/semantic monitoring task (LD/SM) to assess verbal ability  (these tests are better performed by normal heterosexual women than normal heterosexual men), as well as a Water Level Task (WLT) and two Mental Rotation (MR) Tasks designed to assess spatial ability (these tasks are better performed by normal heterosexual men than normal heterosexual women). Results replicated previously reported sex differences between the HT men and women. Further, gay men performed akin to HT women on the verbal task and the MR tasks, but not in the WLT. Lesbians, however, primarily performed in a sex-typical manner.  I suspect though that much, or even most of this small effect actually came from the transsexuals in those samples.   As for such research on lesbians,  I am aware only of one such study which found that lesbians had a more female-like cognitive profile than a male-like one !   They found that the lesbians performed more poorly than heterosexual women on a water jar test of spatial ability (the test requires that the orientation of the water line be recognized as parallel or not to the ground line). Hines and Shipley (1984) found that women exposed in utero to diethylstilbestrol (DES) did however present a masculinized profile of dichotic listening.  Recall that prevalence of lesbianism is higher in these women than in normal controls.