New MRI Studies Support the Blanchard Typology of Male-to-Female Transsexualism

Twoindependentempiricalarticleshaverecentlyappearedintheliterature that, taken together , bear out an hypothesis Blanchard(2008) postulated in the Archives about brain development intranssexualism:[T]he brains of both homosex ual and heterosexual male-to-female transsexuals probably differ from the brains oftypicalheterosexualmen,butindifferentways.Inhomo-sexual male-to-female transsexuals, the difference doesinvolvesex-dimorphicstructures,andthenatureofthedif-ference is a shift in the female -typical direction. If there isany neuroanatomic intersexuality, it is in the homosexualgroup. In heterosexual male-to-female transsexuals, thedifferencemaynotinvolve sex-dimorphic structuresatall,andthenatureofthestructura ldifferenceisnotnecessarilyalong the male–female dimension. (p. 437)Blanchard’s prediction follows from studies that have repeat-edly shown that the homosexual male-to-female transsexualsare‘‘female-shifted’’in multiple, sexually dimorphic character-istics,whereastheheterosexual male-to-femaletranssexualsarenot(Blanchard,1989a,1989b).Forexample,homosexualmale-to-female transsexuals are sexually attracted to natal males,expressgreaterinterestinfemale-typicalactivities(eveninchild-hood), and are naturally effemina te in mannerism. In contrast,heterosexual male-to-female transsexuals are indistinguishablefrom nontranssexual natal males o n these variables. The hetero-sexual transsexuals are still dis tinct from typical males in otherways, however, such as by manif esting ‘‘autogynephilia’’—theeroticinterestinorsexualarousalinresponsetobeingorseemingfemale. The consistent detection of cross-sex features amonghomosexual male-to-female tra nssexuals, but not among heter-osexual male-to-female transse xuals, led Blanchard to predictthat the cross-sex pattern would also emerge at the level of brainanatomyandbelimitedtothehomosexualmale-to-femaletrans-sexuals.Thatpredictionnowappearstobethecase,withRamettiet al. (2010) supporting his prediction for the homosexual trans-sexuals, and Savic and Arver ( 2010), for the heterosexual trans-sexuals.The Rametti team used an MRI technique called DiffusionTensor Imaging to compare homosexual male-to-female trans-sexuals(n=18)withnontranssexual,heterosexualcontrolmales(n=19) and with nontranssexual, h eterosexual control females(n=19). They contrasted the male controls with the femalecontrols to identify the sex-dimorphic portions of the brain andthen contrasted the homosexual transsexuals with each of thecontrol groups on the dimorphic brain regions so identified. Theinitial contrasts identified six sex-dimorphic brain regions. Thehomosexual transsexual sample w as intermediate in volume onall six brain structures, significan tly different from the male con-trolsonfiveofthesix(andsignific antlydifferentfromthefemalecontrols on all six). That is, the se male-to-female transsexualsweredifferentfromthecontrolmales,shiftedtowardsthefemaledirection on all parameters.Savic and Arver (2010) applied anatomical MRIs with ananalogousresearchdesign,identifyingthesex-dimorphicpor-tions of the brain and contrasting the (this time) heterosexualtranssexual sample (n=24) with each control sample (n’s=24each)onthesex-dimorphicbrainregions.Oftheeightbrainregionsthatdistinguishedmalefromfemalebrains,thehetero-sexual transsexual sample differed from the male controls onnone(Savic&Arver,2010,Table3).Ofthefourbrainregionsthat distinguished these heterosexual transsexuals from themale controls, sex-dimorphism was present in none (Savic &Arver,2010,Table3).AsSavicandArverthemselvesempha-sized, ‘‘Contrary to the primary hypothesis, no sex-atypical

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