Effects of sex hormone therapy on interhemispheric crosstalk in postmenopausal women

Evidence exists that fluctuating levels of sex hormones affect interhemispheric interaction in women during the menstrual cycle. The present study investigated whether interhemispheric interaction is susceptible to direct hormonal manipulations via hormone therapy (HT). Sixty-eight postmenopausal women who received HT either with estrogen alone (n = 15), an estrogen-gestagen combination (n = 22) or without HT (n = 31) were investigated. Participants were asked to match letters according to their physical or name identity. Matches were presented either within or across visual half-fields. Additionally, a simple reaction time task, assumed to estimate interhemispheric transfer time (IHTT), was used. Overall, postmenopausal women showed an across-field advantage in the more demanding name-identity task but not in the less demanding physical-identity task. However, across both tasks, the groups differed in responses to within- and across-field trials: the control group performed better on across- than within-field trials, whereas both HT groups showed faster responses on within- than across-field trials. IHTT did not differ between groups. The findings suggest that postmenopausal estrogen-therapy affects the relative efficiency of interhemispheric integration by modulating within-hemisphere functioning.