Cognitive ability and cerebral lateralisation in transsexuals

It is still unclear to what extent cross-gender identity is due to pre- and perinatal organising effects of sex hormones on the brain. Empirical evidence for a relationship between prenatal hormonal influences and certain aspects of gender typical (cognitive) functioning comes from pre- and postpubertal clinical samples, such as women suffering from congenital adrenal hyperplasia and studies in normal children. In order to further investigate the hypothesis that cross-gender identity is influenced by prenatal exposure to (atypical) sex steroid levels we conducted a study with early onset, adult, male-to-female and female-to-male transsexuals, who were not yet hormonally treated, and nontranssexual adult female and male controls. The aim of the study was to find out whether early onset transsexuals performed in congruence with their biological sex or their gender identity The results on different tests show that gender differences were pronounced, and that the two transsexual groups occupied a position in between these two groups, thus showing a pattern of performance away from their biological sex. The findings provide evidence that organisational hormonal influences may have an effect on the development of cross-gender identity.