Hormone therapy in postmenopausal women affects hemispheric asymmetries in fine motor coordination

Evidence exists that the functional differences between the left and right cerebral hemispheres are affected by age. One prominent hypothesis proposes that frontal activity during cognitive task performance tends to be less lateralized in older than in younger adults, a pattern that has also been reported for motor functioning. Moreover, functional cerebral asymmetries (FCAs) have been shown to be affected by sex hormonal manipulations via hormone therapy (HT) in older women. Here, we investigate whether FCAs in fine motor coordination, as reflected by manual asymmetries (MAs), are susceptible to HT in older women. Therefore, sixty-two postmenopausal women who received hormone therapy either with estrogen (E) alone (n=15), an E-gestagen combination (n=21) or without HT (control group, n=26) were tested. Saliva levels of free estradiol and progesterone (P) were analyzed using chemiluminescence assays. MAs were measured with a finger tapping paradigm consisting of two different tapping conditions. As expected, postmenopausal controls without HT showed reduced MAs in simple (repetitive) finger tapping. In a more demanding sequential condition involving four fingers, however, they revealed enhanced MAs in favour of the dominant hand. This finding suggests an insufficient recruitment of critical motor brain areas (especially when the nondominant hand is used), probably as a result of age-related changes in corticocortical connectivity between motor areas. In contrast, both HT groups revealed reduced MAs in sequential finger tapping but an asymmetrical tapping performance related to estradiol levels in simple finger tapping. A similar pattern has previously been found in younger participants. The results suggest that, HT, and E exposure in particular, exerts positive effects on the motor system thereby counteracting an age-related reorganization.