Regional gray matter variation in male-to-female transsexualism

Abstract

Gender identity-one's sense of being a man or a woman-is a fundamental perception experienced by all individuals that extends beyond biological sex. Yet, what contributes to our sense of gender remains uncertain. Since individuals who identify as transsexual report strong feelings of being the opposite sex and a belief that their sexual characteristics do not reflect their true gender, they constitute an invaluable model to understand the biological underpinnings of gender identity. We analyzed MRI data of 24 male-to-female (MTF) transsexuals not yet treated with cross-sex hormones in order to determine whether gray matter volumes in MTF transsexuals more closely resemble people who share their biological sex (30 control men), or people who share their gender identity (30 control women). Results revealed that regional gray matter variation in MTF transsexuals is more similar to the pattern found in men than in women. However, MTF transsexuals show a significantly larger volume of regional gray matter in the right putamen compared to men. These findings provide new evidence that transsexualism is associated with distinct cerebral pattern, which supports the assumption that brain anatomy plays a role in gender identity.

Regional volumes and spatial volumetric distribution of gray matter in the gender dysphoric brain

“…This setup ensured a very reliable sample of 'early-onset' individuals with GD. Savic and Arver (2011) examined GM in 'non-homosexual' MF using VBM and volumetric delineation and did not observe any signs of feminization, and Luders et al (2009b) detected only a localized feminization of the right putamen in primarily 'non-homosexual' MF. Luders et al (2012) also examined cortical thickness in MF, observing some deviations from the natal sex in several regions, although the lack of a female control sample did not facilitate determining whether these deviations reflect signs of feminization.…”

“…MRI studies examining white matter tracts using diffusion tensor imaging have shown deviations from the natal sex in white matter microstructure in both female-to-males (FM) and male-to-females (MF) (Rametti et al, 2011a,b). A few neuroimaging studies have investigated gray matter (GM) in individuals with GD, observing both regional volumetric properties in line with the natal sex and others in line with the gender identity of the GD groups (Luders et al, 2009b(Luders et al, , 2012Savic and Arver, 2011;Zubiaurre-Elorza et al, 2012;Simon et al, 2013). A recent study by Zubiaurre-Elorza et al (2012) was the first to examine GM in FM (ZubiaurreElorza et al, 2012).…”

Male‐to‐female gender dysphoria: Gender‐specific differences in resting‐state networks

“…In auditory processing untreated MtFs showed differences compared with women in earlier and compared with men in higher processing stages. In line with previous structural studies (Luders et al., 2009; Rametti et al., 2011) our data underline the exceptional position of MtFs. Hormonal treatment seems to shift MtFs more toward their aspired gender.…”

“…Thus, MtFs presented a unique pattern of rs‐FC, which cannot be easily assigned to either of the two sexes. This confirms previous findings suggesting an exceptional position of MtFs distinct from men and women (Luders et al., 2009). …”

“…Post‐mortem studies found a similarity in the bed nucleus of the stria terminalis (BSTc) between GD individuals and those of their desired gender (Garcia‐Falgueras & Swaab, 2008; Kruijver et al., 2000). However, in vivo results of studies using structural magnetic resonance imaging (MRI) are more diverse, ranging from no structural differences between men and male‐to‐female GD individuals (MtFs) (Savic & Arver, 2011), differences between MtFs and men and women (Luders et al., 2009), to an intermediate position for hormonally untreated MtFs between male and female brains (Rametti et al., 2011). Female‐like structures in female‐to‐male GD individuals before hormonal treatment (FtMs) (Rametti et al., 2010) and structural changes through hormonal treatment (Rametti et al., 2012) have also been observed.…”