White matter microstructure in female to male transsexuals before cross-sex hormonal treatment. A diffusion tensor imaging study
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Fig. 1
Sex differences maps of fractional anisotropy (FA). FA is lower in female than in male controls in the superior longitudinal fasciculus with a posterior (A) and anterior (B) predominance. Control females also show lower than control male FA values in the forceps minor (C) and the corticospinal tract (D). The group skeleton used for the between group contrast study is green. The red color shows the clusters of significantly decreased FA in female compared to male controls. The threshold for significance was set at p < 0.05 corrected for multiple comparisons.
Fig. 2
Histograms showing the FA means and SD between control females (black), female to male transsexuals (FtM) (red) and control males (green). FtM transsexuals significantly differed from control females in the same white matter cerebral regions in which control males differed from control females. Significant differences between FtM transsexuals and control males are only seen in the corticospinal tract. SLF: Superior longitudinal fasciculus. *at least p < 0.005. (For interpretation of the references to colour in this figure legend the reader is refered to the web version of this article)
Abstract
Background
Some gray and white matter regions of the brain are sexually dimorphic. The best MRI technique for identifying subtle differences in white matter is diffusion tensor imaging (DTI). The purpose of this paper is to investigate whether white matter patterns in female to male (FtM) transsexuals before commencing cross-sex hormone treatment are more similar to that of their biological sex or to that of their gender identity.
Method
DTI was performed in 18 FtM transsexuals and 24 male and 19 female heterosexual controls scanned with a 3 T Trio Tim Magneton. Fractional anisotropy (FA) was performed on white matter fibers of the whole brain, which was spatially analyzed using Tract-Based Spatial Statistics.
Results
In controls, males have significantly higher FA values than females in the medial and posterior parts of the right superior longitudinal fasciculus (SLF), the forceps minor, and the corticospinal tract. Compared to control females, FtM showed higher FA values in posterior part of the right SLF, the forceps minor and corticospinal tract. Compared to control males, FtM showed only lower FA values in the corticospinal tract.
Conclusions
Our results show that the white matter microstructure pattern in untreated FtM transsexuals is closer to the pattern of subjects who share their gender identity (males) than those who share their biological sex (females). Our results provide evidence for an inherent difference in the brain structure of FtM transsexuals.
Keywords:
Diffusion tensor imaging, Transsexualism, Sex differences, Superior longitudinal fasciculus, Forceps minor, Corticospinal tractTo access this article, please choose from the options below
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