In dem Beitrag „Unterschiede im Gehirn von Männern und Frauen: Struktur“ hatte ich bereits eine Studie zitiert, nach der es Unterschiede in der grauen und weißen Gehirnmasse bei Männern und Frauen gibt:
men had roughly 6.5 times the number of GM voxels identified as related to intellectual functioning as did women, and women had roughly nine times more WM voxels than did men. With respect to regional effects, in women, 84% of the identified GM voxels correlated to IQ were in the frontal region, as compared to 45% in men. Even greater sex differences were observed in WM, where for women 86% of the identified voxels were frontal, as compared to 0% in men.
Zwei andere Studien haben nun überprüft, wie dies bei Transsexuellen aussieht:
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.
Quelle: White matter microstructure in female to male transsexuals before cross-sex hormonal treatment. A diffusion tensor imaging study (PDF)
Und für Männer-zu-Frauen-Transsexuellen:
Background: Diffusion tensor imaging (DTI) has been shown to be sensitive in detecting white matter differences between sexes. Before cross-sex hormone treatment female to male transsexuals (FtM) differ from females but not from males in several brain ﬁbers. The purpose of this paper is to investigate whether white matter patterns in male to female (MtF) transsexuals before commencing cross-sex hormone treatment are also more similar to those of their biological sex or whether they are more similar to those of their gender identity.
Method: DTI was performed in 18 MtF transsexuals and 19 male and 19 female controls scanned with a 3 T Trio Tim Magneton. Fractional anisotropy (FA) was performed on white matter of the whole brain, which was spatially analyzed using Tract-Based Spatial Statistics.
Results: MtF transsexuals differed from both male and female controls bilaterally in the superior longitudinal fasciculus, the right anterior cingulum, the right forceps minor, and the right corticospinal tract.
Conclusions: Our results show that the white matter microstructure pattern in untreated MtF transsexuals falls halfway between the pattern of male and female controls. The nature of these differences suggests that some fasciculi do not complete the masculinization process in MtF transsexuals during brain development.
Quelle: The microstructure of white matter in male to female transsexuals before cross-sex hormonal treatment. A DTI study (PDF)
Es passt insoweit zu den Theorien, dass bei Transsexuellen die Formatierung des Gehirns hin zu der üblicherweise bei diesem Phänotyp vorliegenden Gehirnstruktur nicht stattgefunden hat.