Activating effects of cross-sex hormones on cognitive functioning: A study of short-term and long-term hormone effects in transsexuals

In an earlier study we demonstrated that 3 months of cross-sex hormone treatment clearly influenced cognitive functioning in transsexuals. The aims of the present study were to examine: (a) whether we could replicate these findings in a new group of transsexuals; (b) whether a similar pattern of change could be found for novel tasks, i.e. tasks, not used in the previous study, that measured closely related cognitive abilities; (c) whether the cognitive changes following cross-sex hormone treatment had stabilized after 3 months or continued to develop over a period of 1 year; and finally, (d) whether the effects were quickly reversible when the hormone treatment was temporarily stopped. Again a pronounced effect of androgen treatment was found on spatial ability in female-to-male transsexuals (FMs) over a period of one and a half years. As expected, untreated male-to-female transsexuals (MFs) had higher scores on visuo-spatial tasks than untreated FMs; after 3 months of cross-sex hormone treatment, the group difference had disappeared, while after about 10 months of hormone treatment, the sex difference was reversed. These effects did not disappear after termination of cross-sex hormone therapy for a period of 5 weeks, but continued to change slightly in the same direction. Earlier findings of an opposite effect of cross-sex hormones on verbal fluency (i.e. MFs improved and FMs deteriorated after 3 months of cross-sex hormone treatment) were not replicated in this study, nor did we find an hormonal influence on other cognitive functions. This study shows that testosterone had an enhancing, and not quickly reversible effect, on spatial ability performance, but no deteriorating effect on verbal fluency in adult women (FMs). In contrast, anti-androgen treatment in combination with estrogen therapy had no declining effect on spatial ability, nor an enhancing effect on verbal fluency in adult men (MFs).