AUSTIN, Texas —New research at The University of Texas at Austin reveals that the brains of homosexual males and females respond differently to auditory stimuli than do the brains of heterosexuals. When brief acoustic stimuli are presented to the ear, a distinctive series of brain waves is produced -- and the research shows that certain waves differ in their size or timing in homosexuals and heterosexuals. For female subjects identifying themselves as lesbians or bisexuals, the brain waves were intermediate to those of male and female heterosexuals. "There was evidence that the auditory evoked potentials of homosexual and bisexual women were shifted in the male direction," said Dennis McFadden, UT Austin professor of experimental psychology and co-author of the study. "The implication is that some brain structures were masculinized at some time during development," he said. A paper reporting the study's results appears in the July issue of The Journal of the Association for Research in Otolaryngology. Other physical characteristics also are masculinized in homosexual females, according to the research. For example, in heterosexual females the index and fourth fingers are about the same in length, while in males the index finger is shorter than the fourth finger. This sex difference is believed to be produced by differential exposure to male hormones such as testosterone. In homosexual females, the index finger is shorter than in heterosexual females, also suggesting a masculinization effect. "Physiological differences of this sort are highly unlikely to be caused by differences in experience or upbringing," said McFadden. For male subjects identifying themselves as homosexual, the brain waves were shifted away from those of both the heterosexual males and heterosexual females. "A good way to describe the data from the homosexual males is that they appeared to be hyper-masculinized," said Craig Champlin, associate professor of communication sciences and disorders at the University and co-author of the study. "This is especially interesting because other recent experiments have also found hyper-masculinization effects in homosexual males. For example, penis size is greater in homosexuals than in heterosexuals," said Champlin. "Our research reveals that it is not just parts of the body that are hyper-masculinized in homosexual males, but the brain as well," said McFadden. Past research from McFadden's lab showed that the inner ears, or cochleas, of female homosexuals and bisexuals also are masculinized, but this is the first evidence of similar effects in the auditory brain. In other studies, McFadden found no differences between the cochleas of male homosexuals and heterosexuals, so the new findings of differences in their auditory brain waves suggest that the mechanisms producing homosexuality may act differently in males and females. "A large number of physiological and behavioral measures reveal differences between heterosexuals and homosexuals," said McFadden. "The problem for science is to identify the mechanisms--presumably they are hormonal mechanisms--that produce these differences. Our findings suggest that the auditory system may be a valuable, if unlikely, tool for studying those causal mechanisms. Apparently whatever developmental mechanisms are acting to produce homosexuality are also affecting components of the auditory system." "Logic suggests that the degree of exposure to androgens--the male sex hormones--is somehow involved in the production of homosexuality, and our auditory results are generally in accord with that idea," McFadden said. Champlin emphasized that "the differences we have observed were group differences, and it is not possible to determine anyone's sexual orientation from knowledge of his or her auditory brain waves." For both males and females, five separate measures of the auditory brain waves were different in the homosexuals and heterosexuals. All of the waves showing differences appeared within 0.05 seconds following the acoustic stimulus. The auditory brain waves studied by McFadden and Champlin are recorded using electrodes attached to the scalp. They are commonly measured when it is necessary to obtain a physiological assessment of hearing instead of a behavioral one, as with infants. * close this window * go back to the website |