Ulrike Bayer

Interhemispheric interaction during the menstrual cycle

Fluctuating levels of sex hormones and high levels of progesterone (P), in particular, have been suggested to reduce interhemispheric inhibition. The present study focuses on hormone-dependent modulation of interhemispheric integration. In two versions of the Banich-Belger task, participants were asked to match letters according to their physical (e.g., A vs. A) and semantic identity (e.g., A vs. a). Matches were presented either within or across visual half-fields. Moreover, a simple reaction-time task (Poffenberger task) that is assumed to estimate interhemispheric transfer time (IHTT) was used. Seventeen normally cycling women were tested during low P menses and high P midluteal phase. Saliva levels of P were analysed using chemiluminescence assays. Fifteen postmenopausal women performed the same tasks in corresponding time intervals. Additionally, 28 younger male controls were tested once. In agreement with previous results, the more demanding (semantic) interhemispheric-integration task revealed a typical across-field advantage (AFA) for all three groups. However, in normally cycling women, the AFA was significantly reduced during menses. IHTT did not change across the cycle phases. The results indicate that interhemispheric integration fluctuates across the menstrual cycle and is reduced during menses. During the luteal phase, however, the AFA is increased, suggesting that accompanying hormonal conditions favour an efficient interhemispheric integration. We conclude that transcallosal mechanisms involved in interhemispheric integration are profoundly altered when sex hormones are permanently reduced as in men and postmenopausal women. This difference enables an efficient interhemispheric integration without modulatory effects of P.

Estrogen therapy affects right hemisphere functioning in postmenopausal women

It has been suggested that hormone therapy (HT) in postmenopausal women differentially affects verbal and visuo-spatial abilities which mainly rely on left hemisphere (LH) and right hemisphere (RH) functioning, respectively. Thus, it seems likely that HT-related effects on cognition are driven by associated hormonal changes and their impact on functional brain organization, and functional cerebral asymmetries (FCAs) in particular. The present study investigated HT-related effects on FCAs in sixty-seven postmenopausal women who received hormone therapy either with estrogen (E) alone (n=14), an E-gestagen combination (n=22) or without HT (control group, n=31). Saliva levels of free E and progesterone (P) were analyzed using chemiluminescence assays. FCAs were measured with the visual half-field (VHF) technique using a word matching and a figural comparison task. In agreement with previous results, a postmenopausal control group showed a left hemisphere (LH) advantage in the verbal task and a right hemisphere (RH) advantage in visuo-spatial processing. In contrast, both HT groups revealed significantly reduced FCAs in the figural comparison task as a result of an E-related decrease in RH performance. The findings suggest that E-therapy in postmenopausal women can affect visuo-spatial abilities by modulating the functional brain organization and RH functioning in particular.

The influence of sex hormones on functional cerebral asymmetries in postmenopausal women

Studies investigating changes in functional cerebral asymmetries (FCAs) with hormonal fluctuations during the menstrual cycle in young women have led to controversial hypotheses about an influence of estrogen (E) and/or progesterone (P) on FCAs. Based on methodical, but also on principal problems in deriving conclusions about hormone effects from correlational designs, the present study investigated hemispheric asymmetries in postmenopausal women, who received hormone replacement either with E alone (E group, n=32), an E-P combination (E-P group, n=29) or no hormone substitution (control group, n=31). Speed and accuracy of responses to a word- and a face decision task, both presented laterally by means of the visual half field technique, were assessed. The control group showed the typical pattern of hemispheric asymmetry with more correct responses to verbal stimuli presented in the right visual field (RVF) and to face stimuli presented in the left visual field (LVF). A hormone-effect was demonstrable only for the verbal task, in which the E group showed an enhanced performance of the right hemisphere (LVF). The E-P group showed no significant differences to the control group or the E group. The results suggest a role of E in the modulation of FCAs at least with regard to verbal processing.

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.

Right fronto-parietal dysfunction underlying spatial attention in bipolar disorder

Although the neural underpinning of bipolar disorder (BD) is still unknown, recent research suggests that the right fronto-parietal cortex is particularly affected in BD patients. If this were true, we would expect atypical functional cerebral asymmetries in allocation of visuospatial attention. To test this hypothesis, euthymic BD patients and age- and gender-matched healthy controls were compared on the visual line-bisection task, a reliable measure of visuospatial attention, associated with right parietal function. Line bisection performance (i.e. absolute and directional bias) was compared between groups as a function of response hand and line position. The results showed a typical hand-use effect in healthy controls involving a larger leftward bias (i.e. pseudoneglect) with the left hand than with the right hand. Although euthymic BD patients did not differ from healthy controls in the overall accuracy (i.e. absolute bias), they differed significantly in the directional line bisection bias. In contrast to healthy controls, BD patients did not significantly deviate from the veridical center, regardless of which hand was used to bisect horizontal lines. This finding indicates an atypical functional cerebral asymmetry in visuospatial attention in euthymic BD patients, supporting the idea of a dysfunction especially in the right fronto-parietal cortex.

Atypical lateralisation in emotional prosody in men with schizotypy

Individuals high in schizotypy have been shown to reveal reduced lateralisation in verbal processing which may be influenced by an impaired left hemisphere performance. However, little is known about schizotypy and right hemisphere functions such as emotional perception. The present study focuses on atypical lateralisation in language and emotional prosody in Impulsive Non-conformity (IMP), a specific aspect of schizotypy. A total of 41 participants (20 females) performed a dichotic listening linguistic and emotional prosody task, which typically shows a right ear advantage (REA) and left ear advantage (LEA), respectively. A median split based on the IMP scale included in the Oxford-Liverpool Inventory of Feelings and Experiences was used to divide the sample into high and low scorers. The results revealed a selective reduction of the LEA in the prosody task in high-IMP males. Females high and low in IMP revealed typical lateralisation in both tasks. The results indicate that high-IMP males are especially prone to atypical lateralisation in emotional prosody, which parallels those findings in male patients with schizophrenia. The results suggest similarities in sex-specific atypical brain organisation between schizotypy and schizophrenia.

Sex hormone therapy and functional brain plasticity in postmenopausal women

Several studies have shown that fluctuating levels of sex hormones (estrogen and progesterone) can affect fundamental principles of brain organization, including functional cerebral asymmetries (FCAs) and interhemispheric interactions. The majority of findings come from studies investigating younger women tested during distinct hormonal phases of the menstrual cycle, an approach that does not necessarily allow for conclusions about the causal relationship between hormonal changes and functional brain organization. An alternative approach is to manipulate the hormonal status of participants directly. This research focuses on the effects of hormone therapy (HT) on FCAs and interhemispheric interactions in postmenopausal women. Functional brain organization was tested in postmenopausal women using either estrogen therapy or combined estrogen plus gestagen therapy. The results are then compared to age- and IQ-matched postmenopausal women not taking HT. The results indicate HT-related modulations in both FCAs and interhemispheric interaction. In contrast to normally cycling women, however, it seems that HT, and especially estrogen therapy, after menopause affects intrahemispheric processing rather than interhemispheric crosstalk. The findings indicate a faster and more pronounced age-related decline in intrahemispheric relative to interhemispheric processing which seems to be accompanied by a higher sensitivity to HT. Aging processes together with differences in the hormonal status (exogenous changes as a result of HT vs. endogenous changes during the menstrual cycle) may also explain divergent (cognitive) behavioral outcomes in postmenopausal women and younger women. Taken together, the findings suggest that the female brain retains its plasticity even after reproductive age and remains susceptible to the effects of sex hormones throughout the lifetime. This article is part of a Special Issue entitled: Neuroactive Steroids: Focus on Human Brain.

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.

Menstrual cycle-related changes of functional cerebral asymmetries in fine motor coordination

Fluctuating sex hormone levels during the menstrual cycle have been shown to affect functional cerebral asymmetries in cognitive domains. These effects seem to result from the neuromodulatory properties of sex hormones and their metabolites on interhemispheric processing. The present study was carried out to investigate whether functional cerebral asymmetries in fine motor coordination as reflected by manual asymmetries are also susceptible to natural sex hormonal variations during the menstrual cycle. Sixteen right-handed women with a regular menstrual cycle performed a finger tapping paradigm consisting of two conditions (simple, sequential) during the low hormone menstrual phase and the high estrogen and progesterone luteal phase. To validate the luteal phase, saliva levels of free progesterone (P) were analysed using chemiluminescence assays. As expected, normally cycling women showed a substantial decrease in manual asymmetries in a more demanding sequential tapping condition involving four fingers compared with simple (repetitive) finger tapping. This reduction in the degree of dominant (right) hand manual asymmetries was evident during the luteal phase. During the menstrual phase, however, manual asymmetries were even reversed in direction, indicating a slight advantage in favour of the non-dominant (left) hand. These findings suggest that functional cerebral asymmetries in fine motor coordination are affected by sex hormonal changes during the menstrual cycle, probably via hormonal modulations of interhemispheric interaction.

Estrogen treatment affects brain functioning after menopause

Sex hormones have powerful neuromodulatory effects on functional brain organization and cognitive functioning. This paper reviews findings from studies investigating the influence of sex hormones in postmenopausal women with and without hormone therapy (HT). Functional brain organization was investigated using different behavioural tasks in postmenopausal women using either estrogen therapy or combined estrogen plus gestagen therapy and age- and IQ-matched postmenopausal women not taking HT. The results revealed HT-related modulations in specific aspects of functional brain organization including functional cerebral asymmetries and interhemispheric interaction. In contrast to younger women during the menstrual cycle, however, it seems that HT, and especially estrogen therapy, after menopause affects intrahemispheric processing rather than interhemispheric interaction. This might be explained by a faster and more pronounced age-related decline in intrahemispheric relative to interhemispheric functioning, which might be associated with higher sensitivity to HT. Taken together, the findings suggest that the female brain retains its plasticity even after reproductive age and remains susceptible to the effects of sex hormones throughout the lifetime, which might help to discover new clinical approaches in the hormonal treatment of neurological and psychiatric disorders.