The term transgender refers to the incongruence between an individually experienced and manifested gender with a sex assigned at birth (natal). Gender dysphoria refers to the distress caused by this incongruence, which can lead to a social, occupational or emotional disorder. Research in the field of gender identity, gender dysphoria and gender incongruence, due to the complex nature of the phenomenon, are very complicated. Nevertheless, researchers have noticed that pathophysiology of gender dysphoria is not sufficiently understandable. Modern models of gender identity development, both typical and atypical, are based on multifactorial etiology and the synergy of numerous genetic, epigenetic and developmental factors. Significant sources of knowledge transgender phenomena are clinical phenomena (DSD - disorder of sexual development, or developmental anomalies - children with unspecified sexuality: congenital adrenal hyperplasia - KAH, androgen-related insensitivity syndrome - AIS, monitoring and follow-up of the development of gender atypical, incongruent and dysphoric children and neurobiological studies of neurovizualization). The current paper focuses on the review of modern neurobiological studies of the brain of transgender individuals. The results of in vivo neuroimaging studies related to the etiology of feelings of gender incongruity, based on the hypothesis of sexual differentiation are presented. The aim of these studies is to answer the question whether the brain of transgender individuals is like the brain of the same gender at birth or those with the same gender-related feelings. Neuroimaging studies in this field are primarily focused on the brain phenotype of transmen and transwomen, with the assumption that they differ in a number of ways from the control group of men and women (sex and gender congruent) with feminine, masculine, de masculinised and de feminised manifestations. Knowledge of the brain phenotype of people with a feelings of gender incongruity could contribute to the answering the question of whether full differentiation of the brain in these people is atypical. Such knowledge could further contribute to knowledge of the gender identity development itself. Imaging studies related to tasks have as a goal to show whether cerebral activation and performance is performed after receiving tasks completely atypical in transgender individuals. The third type of study in this field deals with the evaluation of the effects of the application of full hormones on the brain, which provides insight into how the changes in the level of sex hormones can affect brain structures and their function. The obtained phenotypes can have theoretical implications for brain intersection, asymmetry and body perception in people with gender dysphoria.
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