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

In an earlier study we demonstrated that 3 months of cross-sex hormone trea tment clearly influenced cognitive functioning in transsexuals. The aims of the present study were to examine: (a) whether we could replicate these fi ndings in a new group of transsexuals; (b) whether a similar pattern of cha nge could be found for novel tasks, i.e. tasks, not used in the previous st udy, that measured closely related cognitive abilities; (c) whether the cog nitive changes following cross-sex hormone treatment had stabilized after 3 months or continued to develop over a period of 1 year; and finally, (d) w hether the effects were quickly reversible when the hormone treatment was t emporarily stopped. Again a pronounced effect of androgen treatment was fou nd 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 m onths of cross-sex hormone treatment, the group difference had disappeared, while after about 10 months of hormone treatment, the sex difference was r eversed. These effects did not disappear after termination of cross-sex hor mone therapy for a period of 5 weeks, but continued to change slightly in t he same direction. Earlier findings of an opposite effect of cross-sex horm ones on verbal fluency (i.e. MFs improved and FMs deteriorated after 3 mont hs of cross-sex hormone treatment) were not replicated in this study, nor d id we find an hormonal influence on other cognitive functions. This study s hows that testosterone had an enhancing, and not quickly reversible effect, on spatial ability performance, but no deteriorating effect on verbal flue ncy in adult women (FMs). In contrast, anti-androgen treatment in combinati on with estrogen therapy had no declining effect on spatial ability, nor an enhancing effect on verbal fluency in adult men (MFs). (C) 1999 Elsevier S cience Ltd. All rights reserved.