Transsexuals harbor the strong feeling of having been born to the wrong sex. There is a continuing controversial discussion of whether or not transsexualism has a biological representation. Differences between males and females in terms of functional imaging during erotic stimuli have been previously described, revealing gender-specific results.
Therefore, we postulated that male-to-female (MTF) transsexuals may show specific cerebral activation differing from their biological gender.
Cerebral activation patterns during viewing of erotic film excerpts in functional magnetic resonance imaging (fMRI).
Twelve male and 12 female heterosexual volunteers and 12 MTF transsexuals before any treatment viewed erotic film excerpts during fMRI. Additionally, subjective rating of sexual arousal was assessed. Statistics were performed using the Statistical Parametric Mapping software.
Significantly enhanced activation for men compared with women was revealed in brain areas involved in erotic processing, i.e., the thalamus, the amygdala, and the orbitofrontal and insular cortex, whereas no specific activation for women was found. When comparing MTF transsexuals with male volunteers, activation patterns similar to female volunteers being compared with male volunteers were revealed. Sexual arousal was assessed using standard rating scales and did not differ significantly for the three groups.
We revealed a cerebral activation pattern in MTF transsexuals compared with male controls similar to female controls compared with male controls during viewing of erotic stimuli, indicating a tendency of female-like cerebral processing in transsexualism.
"To address this question, we examined behavioral and brain responses to sexually arousing stimuli, given the prominent sex differences in this domain (Gizewski et al., 2009; Hamann et al., 2004; Ponseti et al., 2006; Sylva et al., 2013; Whittle et al., 2011). In the first functional neuroimaging study of women with CAIS, we used fMRI to examine brain responses to sexually arousing images compared to those typical of control men and women. "
[Show abstract][Hide abstract] ABSTRACT: Androgens, estrogens, and sex chromosomes are the major influences guiding sex differences in brain development, yet their relative roles and importance remain unclear. Individuals with complete androgen insensitivity syndrome (CAIS) offer a unique opportunity to address these issues. Although women with CAIS have a Y chromosome, testes, and produce male-typical levels of androgens, they lack functional androgen receptors preventing responding to their androgens. Thus, they develop a female physical phenotype, are reared as girls, and develop into women. Because sexually differentiated brain development in primates is determined primarily by androgens, but may be affected by sex chromosome complement, it is currently unknown whether brain structure and function in women with CAIS is more like that of women or men. In the first functional neuroimaging study of (46,XY) women with CAIS, typical (46,XX) women, and typical (46, XY) men, we found that men showed greater amygdala activation to sexual images than did either typical women or women with CAIS. Typical women and women with CAIS had highly similar patterns of brain activation, indicating that a Y chromosome is insufficient for male-typical human brain responses. Because women with CAIS produce male-typical or elevated levels of testosterone which is aromatized to estradiol these results rule out aromatization of testosterone to estradiol as a determinate of sex differences in patterns of brain activation to sexual images, We cannot, however, rule out an effect of social experience on the brain responses of women with CAIS as all were raised as girls.
Hormones and Behavior 10/2014; 66(5). DOI:10.1016/j.yhbeh.2014.09.013 · 4.63 Impact Factor
"In this context, previous results and interpretations of regional differences suggest a transition from the biological sex to the actual gender identity. Although feminization and masculinization indeed occurs, for example for neuronal cell number (Zhou et al. 1995; Kruijver et al. 2000; Garcia-Falgueras and Swaab 2008) and activation (Gizewski et al. 2009) as well as gray matter volume (Simon et al. 2013) and cortical thickness (Zubiaurre-Elorza et al. 2013), the identification of unique features of transsexual patients has been largely neglected in previous work. For instance, such an evaluation was impeded by the lack of both control groups in studies of cortical thickness (Luders et al. 2012), cerebral blood flow (Nawata et al. 2010) as well as functional MRI (Schoning et al. 2010) and connectivity (Ku et al. 2013). "
[Show abstract][Hide abstract] ABSTRACT: Although previous investigations of transsexual people have focused on regional brain alterations, evaluations on a network level, especially those structural in nature, are largely missing. Therefore, we investigated the structural connectome of 23 female-to-male (FtM) and 21 male-to-female (MtF) transgender patients before hormone therapy as compared with 25 female and 25 male healthy controls. Graph theoretical analysis of whole-brain probabilistic tractography networks (adjusted for differences in intracranial volume) showed decreased hemispheric connectivity ratios of subcortical/limbic areas for both transgender groups. Subsequent analysis revealed that this finding was driven by increased interhemispheric lobar connectivity weights (LCWs) in MtF transsexuals and decreased intrahemispheric LCWs in FtM patients. This was further reflected on a regional level, where the MtF group showed mostly increased local efficiencies and FtM patients decreased values. Importantly, these parameters separated each patient group from the remaining subjects for the majority of significant findings. This work complements previously established regional alterations with important findings of structural connectivity. Specifically, our data suggest that network parameters may reflect unique characteristics of transgender patients, whereas local physiological aspects have been shown to represent the transition from the biological sex to the actual gender identity.
"However, the majority of the participants in this study were already on hormonal treatment. More recent studies, using participants before the start of treatment, did find similarities between transsexuals and controls with the same gender identity in white matter microstructure (FtM transsexuals, Rametti et al., 2011a), hypothalamic activation while smelling odourous steroids (MtF's, Berglund et al., 2008), brain activation patterns while viewing erotic videos (MtF's, Gizewski et al., 2009), and sources in EEG frequencies (MtF's, Flor-Henry, 2010). In addition, untreated transsexuals differed from controls of their natal sex in regional cerebral blood flow in the left anterior cingulate cortex and right insula (FtM's, Nawata et al., 2010) and brain activation during mental rotation (Schöning et al., 2010). "
[Show abstract][Hide abstract] ABSTRACT: This article is part of a Special Issue "Puberty and Adolescence".This article aims to provide an outline of what is currently known on trajectories, and contributing factors to gender identity development in adolescence. We give a historical overview of the concept of gender identity, and describe general identity development in adolescence, gender identity development in the general population and in gender variant youth. Possible psychosocial (such as child and parental characteristics) and biological factors (such as the effects of prenatal exposure to gonadal hormones and the role of genetics) contributing to a gender variant identity are discussed. Studies focusing on a number of psychosocial and biological factors separately, indicate that each of these factors influence gender identity formation, but little is known about the complex interplay between the factors, nor about the way individuals themselves contribute to the process. Research into normative and gender variant identity development of adolescents is clearly lagging behind. However, studies on persons with gender dysphoria and disorders of sex development, show that the period of adolescence, with its changing social environment and the onset of physical puberty, seems to be crucial for the development of a non-normative gender identity.
Hormones and Behavior 07/2013; 64(2):288-97. DOI:10.1016/j.yhbeh.2013.02.020 · 4.63 Impact Factor
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