Estrogen therapy affects right hemisphere functioning in postmenopausal women

Male-to-female gender dysphoria: Gender-specific differences in resting-state networks

INTRODUCTION

Recent research found gender-related differences in resting-state functional connectivity (rs-FC) measured by functional magnetic resonance imaging (fMRI). To the best of our knowledge, there are no studies examining the differences in rs-FC between men, women, and individuals who report a discrepancy between their anatomical sex and their gender identity, i.e. gender dysphoria (GD).

METHODS

To address this important issue, we present the first fMRI study systematically investigating the differences in typical resting-state networks (RSNs) and hormonal treatment effects in 26 male-to-female GD individuals (MtFs) compared with 19 men and 20 women.

RESULTS

Differences between male and female control groups were found only in the auditory RSN, whereas differences between both control groups and MtFs were found in the auditory and fronto-parietal RSNs, including both primary sensory areas (e.g. calcarine gyrus) and higher order cognitive areas such as the middle and posterior cingulate and dorsomedial prefrontal cortex. Overall, differences in MtFs compared with men and women were more pronounced before cross-sex hormonal treatment. Interestingly, rs-FC between MtFs and women did not differ significantly after treatment. When comparing hormonally untreated and treated MtFs, we found differences in connectivity of the calcarine gyrus and thalamus in the context of the auditory network, as well as the inferior frontal gyrus in context of the fronto-parietal network.

CONCLUSION

Our results provide first evidence that MtFs exhibit patterns of rs-FC which are different from both their assigned and their aspired gender, indicating an intermediate position between the two sexes. We suggest that the present study constitutes a starting point for future research designed to clarify whether the brains of individuals with GD are more similar to their assigned or their aspired gender.

How brain asymmetry relates to performance - a large-scale dichotic listening study

All major mental functions including language, spatial and emotional processing are lateralized but how strongly and to which hemisphere is subject to inter- and intraindividual variation. Relatively little, however, is known about how the degree and direction of lateralization affect how well the functions are carried out, i.e., how lateralization and task performance are related. The present study therefore examined the relationship between lateralization and performance in a dichotic listening task for which we had data available from 1839 participants. In this task, consonant-vowel syllables are presented simultaneously to the left and right ear, such that each ear receives a different syllable. When asked which of the two they heard best, participants typically report more syllables from the right ear, which is a marker of left-hemispheric speech dominance. We calculated the degree of lateralization (based on the difference between correct left and right ear reports) and correlated it with overall response accuracy (left plus right ear reports). In addition, we used reference models to control for statistical interdependency between left and right ear reports. The results revealed a u-shaped relationship between degree of lateralization and overall accuracy: the stronger the left or right ear advantage, the better the overall accuracy. This u-shaped asymmetry-performance relationship consistently emerged in males, females, right-/non-right-handers, and different age groups. Taken together, the present study demonstrates that performance on lateralized language functions depends on how strongly these functions are lateralized. The present study further stresses the importance of controlling for statistical interdependency when examining asymmetry-performance relationships in general.

Sex hormonal modulation of interhemispheric transfer time

It is still a matter of debate whether functional cerebral asymmetries (FCA) of many cognitive processes are more pronounced in men than in women. Some evidence suggests that the apparent reduction in women's FCA is a result of the fluctuating levels of gonadal steroid hormones over the course of the menstrual cycle, making their FCA less static than for men. The degree of lateralization has been suggested to depend on interhemispheric communication that may be modulated by gonadal steroid hormones. Here, we employed visual-evoked EEG potentials to obtain a direct measure of interhemispheric communication during different phases of the menstrual cycle. The interhemispheric transfer time (IHTT) was estimated from the interhemispheric latency difference of the N170 component of the visual-evoked potential from either left or right visual field presentation. Nineteen right-handed women with regular menstrual cycles were tested twice, once during the menstrual phase, when progesterone and estradiol levels are low, and once during the luteal phase when progesterone and estradiol levels are high. Plasma steroid levels were determined by blood-based immunoassay at each session. It was found that IHTT, in particular from right-to-left, was generally longer during the luteal phase relative to the menstrual phase. This effect occurred as a consequence of a slowed absolute N170 latency of the indirect pathway (i.e. left hemispheric response after LVF stimulation) and, in particular, a shortened latency of the direct pathway (i.e. right hemispheric response after LVF stimulation) during the luteal phase. These results show that cycle-related effects are not restricted to modulation of processes between hemispheres but also apply to cortical interactions, especially within the right hemisphere. The findings support the view that plastic changes in the female brain occur during relatively short-term periods across the menstrual cycle.

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.

Oral contraceptive therapy modulates hemispheric asymmetry in spatial attention

BACKGROUND

Functional cerebral asymmetries (FCAs) are known to fluctuate across the menstrual cycle. The visual line-bisection task administered to normally cycling women showed different patterns of the interhemispheric interactions during menses and the midluteal cycle phase. However, the contribution of estrogens and progestins hormones to this phenomenon is still unclear.

STUDY DESIGN

The aim of our study was to show a variation of FCAs in women administered oral contraceptives (OCs) using the visual line-bisection task. Visual line-bisection task with three horizontal lines was administered to 36 healthy women taking a 21-day OC. Twenty-nine patients were right handed. The task was administered during OC intake (day 10) and at the end of the pill-free period.

RESULTS

The right-handed women showed a significant leftward bias of veridical center on the first and third lines during OC intake compared with an opposite rightward bias during the pill-free period. The same phenomenon of contralateral deviation was observed in left-handed women on day 10 of OC intake.

CONCLUSIONS

The results of this study confirm a hormonal modulation on interhemispheric interaction and suggest that OCs may improve the interhemispheric interaction reducing FCAs compared with the low hormone level period. This opens new insights in OC prescription and choice of administration schedule in order to improve cognitive performances.

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.

Dynamic changes in functional cerebral connectivity of spatial cognition during the menstrual cycle

Functional cerebral asymmetries (FCAs) in women have been shown to vary with changing levels of sex hormones during the menstrual cycle. Previous studies have suggested that interhemispheric interaction forms a key component in generating FCAs and it has been shown behaviorally and by functional imaging that interhemispheric interaction changes during the menstrual cycle, at least for a left hemisphere dominant task. We used functional MRI and an analysis of functional connectivity to examine whether changes in right hemisphere advantage for a figure comparison task as found in behavioral studies, are based on comparable mechanisms like those identified for the verbal task. Women were examined three times during the menstrual cycle, during the menstrual, follicular and luteal phases. The behavioral data confirmed the right hemisphere advantage for the figure comparison task as well as changes of the right hemisphere advantage during the menstrual cycle. Imaging data showed cycle phase-related changes in lateralized brain activation within the task-dominant hemisphere and changes in connectivity between nonhomotopic areas of both hemispheres, suggesting that changes in functional brain organization in women during the menstrual cycle are not only restricted to hormone-related changes of interhemispheric inhibition between homotopic areas, as has been proposed earlier, but might additionally apply to changes of neuronal processes within the hemispheres which seem to be modulated by heterotopic functional connectivity between hemispheres.

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.

Effects of conjugated equine estrogens on cognition and affect in postmenopausal women with prior hysterectomy

CONTEXT

Different menopausal hormone therapies may have varied effects on specific cognitive functions. We previously reported that conjugated equine estrogens (CEE) with medroxyprogesterone acetate had a negative impact on verbal memory but tended to impact figural memory positively over time in older postmenopausal women.

OBJECTIVE

The objective of the study was to determine the effects of unopposed CEE on changes in domain-specific cognitive function and affect in older postmenopausal women with prior hysterectomy.

DESIGN

This was a randomized, double blind, placebo-controlled clinical trial.

SETTING

The study was conducted at 14 of 40 Women's Health Initiative (WHI) clinical centers.

PARTICIPANTS

Participants were 886 postmenopausal women with prior hysterectomy, aged 65 yr and older (mean 74 yr), free of probable dementia, and enrolled in the WHI and WHI Memory Study (WHIMS) CEE-Alone trial for a mean of 3 yr and followed up for a mean of 2.70 yr.

INTERVENTION

Intervention was 0.625 mg of CEE daily or placebo.

MAIN OUTCOME MEASURES

Annual rates of change in specific cognitive functions and affect, adjusted for time since randomization, were measured.

RESULTS

Compared with placebo, unopposed CEE was associated with lower spatial rotational ability (P < 0.01) at initial assessment (after 3 yr of treatment), a difference that diminished over 2.7 yr of continued treatment. CEE did not significantly influence change in other cognitive functions and affect.

CONCLUSIONS

CEE did not improve cognitive functioning in postmenopausal women with prior hysterectomy. CEE was associated with lower spatial rotational performance after an average of 3 yr of treatment. Overall, CEE does not appear to have enduring effects on rates of domain-specific cognitive change in older postmenopausal women.

Sex Hormones: Modulators of Interhemispheric Inhibition in the Human Brain

Functional cerebral asymmetries (FCAs), which constitute a basic principle of human brain organization, are supposedly generated by interhemispheric inhibition of the dominant on the nondominant hemisphere. It has repeatedly been shown that FCAs are sex specific: While they are relatively stable in men, they change during the menstrual cycle in women, indicating that sex hormones might play an important role in modulating functional brain organization and brain asymmetries in particular. Modern brain imaging techniques like functional magnetic resonance imaging (fMRI) allow for the noninvasive study of the mechanisms underlying changing FCAs. Imaging data show that in women the inhibitory influence of the dominant on the nondominant hemisphere is reduced with rising levels of sex hormones in the course of the menstrual cycle. Apart from modulating interhemispheric inhibition, sex hormones also seem to change functional organization within hemispheres. These results reveal a powerful neuromodulatory action of sex hormones on the dynamics of functional brain organization in the female brain. They may further contribute to the ongoing discussion of sex differences in brain function in that they help explain the dynamic part of functional brain organization in which the female differs from the male brain.