Steroid fluctuations modify functional cerebral asymmetries: the hypothesis of progesterone-mediated interhemispheric decoupling

Performance of fine motor and spatial tasks during the menstrual cycle

Various studies have shown fluctuations in task performance during the menstrual cycle. The aim of this study was to see the effects of the menstrual cycle on performing fine motor and spatial tasks of different level of complexity in twenty students aged 18 to 21 years, with regular menstrual cycle (28 to 30 days). The students performed O'Connor Finger Dexterity Test and mental rotation test during the menstrual, late follicular, and midluteal phase. Before the tests were performed, we administered Spielberger's State-Trait Anxiety Inventory for each phase. After the tasks were completed, the subjects ranked their difficulty on Borg's scale.The results showed the best performance in both tests in the midluteal phase (with sex hormones at their peak). The anxiety level and task difficulty ranking were the highest in the menstrual phase, when the hormone levels were the lowest.

Hormones and dichotic listening: evidence from the study of menstrual cycle effects

This report presents evidence for changes in dichotic listening asymmetries across the menstrual cycle, which replicate studies from our laboratory and others. Increases in the right ear advantage (REA) were present in women at phases of the menstrual cycle associated with higher levels of ovarian hormones. The data also revealed correlations between hormone levels and behavioural measures of asymmetry. For example, the pre-ovulatory surge in luteinising hormone (LH) was related to a decrease in left ear scores, which comprised a key part of the cycle related shift in asymmetry. Further analysis revealed a subgroup of women who had not reached postovulatory status by days 18-25 of the cycle, as verified by low progesterone levels. These women showed laterality profiles at days 18-25 that looked more like the other women when measured at the periovulatory phase (i.e., days 8-11). Data were combined with those from a previous study to highlight the stability of effects. Results showed a distinct menstrual cycle related increase in asymmetry in the combined sample. This final comparison confirmed the nature of sex differences in dichotic listening as being dependent on hormone status in women.

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.

The influence of tobacco consumption on the relationship between schizotypy and hemispheric asymmetry

Tobacco use is positively associated with severity of symptoms along the schizophrenia spectrum. Accordingly it could be argued that neuropsychological performance, formerly thought to be modulated by schizotypy, is actually modulated by drug use or an interaction of drug use and schizotypy. We tested whether habitual cigarette smokers as compared to non-smokers would show a neuropsychological profile similar to that observed along the schizophrenia spectrum and, if so, whether smoking status or nicotine dependence would be more significant modulators of behavior than schizotypy. Because hemispheric dominance has been found to be attenuated along the schizophrenia spectrum, 40 right-handed male students (20 non-smokers) performed lateralized left- (lexical decisions) and right- (facial decision task) hemisphere dominant tasks. All individuals completed self-report measures of schizotypy and nicotine dependence. Schizotypy predicted laterality in addition to smoking status: While positive schizotypy (Unusual Experiences) was unrelated to hemispheric performance, Cognitive Disorganization predicted reduced left hemisphere dominant language functions. These latter findings suggest that Cognitive Disorganization should be regarded separately as a potentially important mediator of thought disorganization and language processing. Additionally, increasing nicotine dependence among smokers predicted a right hemisphere shift of function in both tasks that supports the role of the right hemisphere in compulsive/impulsive behavior.

Is infant holding-side bias related to motor asymmetries in mother and child?

Studies have revealed a preference for the left hemibody in infant holding in 65-85% of cases. Several investigations have linked this preference to maternal asymmetries. The main goal of the present study was to assess manual and hemispheric asymmetries in both mother and child and delineate their respective influence on holding-side biases. Holding side was assessed by direct observation, and by use of a questionnaire within populations of mother-child dyads. Maternal asymmetries were handedness and hemispheric specialization for perceiving emotions. Infant asymmetries were fetal position, asymmetric tonic neck reflex (ATNR) at birth and handedness at 19 months of age. To that purpose a longitudinal study has been made with infants observed at 2 and 19 months of age. A significant relationship was found between maternal handedness and holding preferences, but no significant relation was obtained between hemispheric specialization and holding preferences. Fetal position in utero but not ATNR, was significantly related to holding-side preferences. Finally, holding side at 2 months was significantly associated with infants' unimanual preferences.

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.

Sex-related differences in the hemispheric laterality of slow cortical potentials during the preparation of visually guided movements

Previous work suggests the presence of sex differences in the laterality of brain activity in the premotor-parietal network during the preparation of visually guided reaching movements. In the current study, electroencephalography was used to test the hypothesis that women would have higher amplitude potentials over frontal and parietal regions ipsilateral to arm movements, relative to men. Event-related slow cortical potentials (SCPs) were collected from 30 participants (15 men and 15 women) during the performance of two visually guided reaching conditions (eyes and arm moved to the same spatial location or moved in opposite directions). The results of the study demonstrate that the amplitudes of SCPs were significantly higher overlying frontal regions of the right hemisphere of women relative to men. These differences were present both during an instructed-delay period prior to receiving a go-signal to initiate movement and during the period just prior to movement initiation. The study also revealed an interaction of Sex and Condition in the parietal region during the pre-movement period. These results suggest that motor preparatory activity in men mainly occurs in the hemisphere contralateral to reaching but that preparatory activity in women is distributed relatively more bilaterally. However, the nature of these differences changes over the time course of the preparatory period and is partially dependent on the type of visuomotor mapping being performed.

Brain estrogens rapidly strengthen auditory encoding and guide song preference in a songbird

Higher cognitive function depends on accurate detection and processing of subtle features of sensory stimuli. Such precise computations require neural circuits to be modulated over rapid timescales, yet this modulation is poorly understood. Brain-derived steroids (neurosteroids) can act as fast signaling molecules in the vertebrate central nervous system and could therefore modulate sensory processing and guide behavior, but there is no empirical evidence for this possibility. Here we report that acute inhibition of estrogen production within a cortical-like region involved in complex auditory processing disrupts a songbird's ability to behaviorally respond to song stimuli. Identical manipulation of local estrogen levels rapidly changes burst firing of single auditory neurons. This acute estrogen-mediated modulation targets song and not other auditory stimuli, possibly enabling discrimination among species-specific signals. Our results demonstrate a crucial role for neuroestrogen synthesis among vertebrates for enhanced sensory encoding. Cognitive impairments associated with estrogen depletion, including verbal memory loss in humans, may therefore stem from compromised moment-by-moment estrogen actions in higher-order cortical circuits.

Estradiol levels during the menstrual cycle differentially affect latencies to right and left hemispheres during dichotic listening: an ERP study

Many behavioral studies have found high-estrogen phases of the menstrual cycle to be associated with enhanced left-hemisphere processing and low-estrogen phases to be associated with better right-hemisphere processing. This study examined the changing of hemispheric asymmetry during the menstrual cycle by analyzing event-related potential (ERP) data from midline and both hemispheres of 23 women during their performance of a dichotic tasks shown to elicit a left-hemisphere response (semantic categorization) and a right-hemisphere response (complex tones). Each woman was tested during her high-estrogen follicular phase and low-estrogen menstrual phase. Salivary assays of estradiol and progesterone were used to confirm cycle phase. Analyses of the ERP data revealed that latency for each hemisphere was differentially affected by phase and target side, such that latencies to the left hemisphere and from the right ear were shorter during the high-estrogen phase, and latencies to the right hemisphere and from the left ear were shorter during the low-estrogen phase. These findings supply electrophysiological correlates of the cyclically based interhemispheric differences evinced by behavioral studies.

Sex differences in the adolescent brain

Adolescence is a time of increased divergence between males and females in physical characteristics, behavior, and risk for psychopathology. Here we will review data regarding sex differences in brain structure and function during this period of the lifespan. The most consistent sex difference in brain morphometry is the 9-12% larger brain size that has been reported in males. Individual brain regions that have most consistently been reported as different in males and females include the basal ganglia, hippocampus, and amygdala. Diffusion tensor imaging and magnetization transfer imaging studies have also shown sex differences in white matter development during adolescence. Functional imaging studies have shown different patterns of activation without differences in performance, suggesting male and female brains may use slightly different strategies for achieving similar cognitive abilities. Longitudinal studies have shown sex differences in the trajectory of brain development, with females reaching peak values of brain volumes earlier than males. Although compelling, these sex differences are present as group averages and should not be taken as indicative of relative capacities of males or females.

Menstrual cycle phase effects on memory and Stroop task performance

The present study examined differences in Stroop and memory task performances modulated by gonadal steroid hormones during the menstrual cycle in women. Thirty women with regular menstrual cycles performed a logical memory task (Wechsler Memory Scale) and the Stroop task. The results showed a significant difference in Stroop task performance between low and high levels of estradiol and progesterone during the menstrual cycle, but there was no significant difference in memory performance between the two phases, nor was there any significant mood change that might have influenced cognitive performance. These findings suggest that sex-related hormone modulation selectively affects cognitive functions depending on the type of task and low level secretion of estradiol appears to contribute to reducing the level of attention that relates to the prefrontal cortex.

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.

Sex Hormones and Cognitive Functioning of Women

U radu se raspravlja o organizirajućim i aktivirajućim učincima spolnih hormona te o njihovu utjecaju na kognitivno funkcioniranje. Dosadašnja su istraživanja pokazala spolne razlike u nekim specifičnim kognitivnim sposobnostima. Žene su u prosjeku bolje u verbalnoj fluentnosti, perceptivnoj brzini i točnosti, kao i finijoj motorici, dok su muškarci u prosjeku bolji u prostornim i matematičkim sposobnostima. Ove razlike u kognitivnom funkcioniranju dovode se u vezu s izlaganjem mozga fetusa različitim razinama spolnih hormona tijekom prenatalnog života. Studije na skupinama rođenim s genskim poremećajima, kao što su sindrom neosjetljivosti na androgene, kongenitalna adrenalna hiperplazija i Turnerov sindrom također upućuju na organizirajuće učinke spolnih hormona na kognitivno funkcioniranje.

Nadalje, dosadašnja istraživanja pokazuju da povišene razine ženskih spolnih hormona u kasnoj folikularnoj i/ili lutealnoj fazi menstrualnog ciklusa potenciraju tipičan ženski kognitivni obrazac funkcioniranja, koji karakterizira veća učinkovitost u zadacima koje u prosjeku bolje rješavaju žene. Niske pak razine ovih hormona, koje karakteriziraju menstrualnu fazu ciklusa, potenciraju tipičan muški obrazac funkcioniranja, koji uključuje bolju učinkovitost u zadacima koje u prosjeku bolje rješavaju muškarci.

U radu se također raspravlja o metodološkim razlikama u dosadašnjim istraživanjima organizirajućih i aktivirajućih učinaka spolnih hormona na kognitivno funkcioniranje, kao i o smjernicama za buduća istraživanja.

Hormone exposure and functional lateralisation: examining the contributions of prenatal and later life hormonal exposure

An increasing amount of research has shown a relationship between hormonal exposure and functional lateralisation. In this study different sources of hormonal exposure were examined: prenatal exposure, estimated using the 2D:4D ratio, and later life exposure through examining the effects of hormone replacement therapy. In addition to considering multiple sources of hormonal exposure, three tests of functional lateralisation were used: two versions of the chimeric faces test, one using positive emotion and the other using negative emotion, and the landmark task. The same effects were found across all three measures of lateralisation. Lower 2D:4D ratios, which indicate high levels of prenatal testosterone exposure, were associated with stronger right hemisphere dominance. Later life hormonal exposure was not found to be associated with any of the lateralisation measures. This finding suggests a relationship between prenatal hormonal exposure and brain organisation.

Putative sex differences in verbal abilities and language cortex: a critical review

This review brings together evidence from a diverse field of methods for investigating sex differences in language processing. Differences are found in certain language-related deficits, such as stuttering, dyslexia, autism and schizophrenia. Common to these is that language problems may follow from, rather than cause the deficit. Large studies have been conducted on sex differences in verbal abilities within the normal population, and a careful reading of the results suggests that differences in language proficiency do not exist. Early differences in language acquisition show a slight advantage for girls, but this gradually disappears. A difference in language lateralization of brain structure and function in adults has also been suggested, perhaps following size differences in the corpus callosum. Neither of these claims is substantiated by evidence. In addition, overall results from studies on regional grey matter distribution using voxel-based morphometry, indicate no consistent differences between males and females in language-related cortical regions. Language function in Wada tests, aphasia, and in normal ageing also fails to show sex differentiation.

Short-term changes in endogenous estrogen levels and consumption of soy isoflavones affect working and verbal memory in young adult females

Estrogen is known to modulate certain cognitive functions, most notably improving working memory and verbal memory. Soy foods contain isoflavones, phytoestrogens structurally similar to estrogen that weakly bind to estrogen receptors. We investigated the effects of natural variations in estrogen levels and short-term dietary supplementation with soy isoflavones on cognitive function in 28 young women. Performance was examined across a range of cognitive tasks on three occasions during separate menstrual cycles: during a menses phase (low estrogen), during a luteal phase (highest estrogen), and once during a menses phase after a 3-day phytoestrogen-rich dietary intervention. Soy supplementation during menses led to an improvement in working memory and verbal memory. The menstrual cycle effects were mixed, with high estrogen improving performance on a verbal memory task but not on working memory. Our results suggest that soy phytoestrogens may improve working memory through estrogen-independent mechanisms.

Estradiol modulates functional brain organization during the menstrual cycle: an analysis of interhemispheric inhibition

According to the hypothesis of progesterone-mediated interhemispheric decoupling (Hausmann and Güntürkün, 2000), functional cerebral asymmetries (FCAs), which are stable in men and change during the menstrual cycle in women, are generated by interhemispheric inhibition of the dominant on the nondominant hemisphere. The change of lateralization during the menstrual cycle in women might indicate that sex hormones play an important role in modulating FCAs. We used functional magnetic resonance imaging to examine the role of estradiol in determining cyclic changes of interhemispheric inhibition. Women performed a word-matching task, while they were scanned twice during the cycle, once during the menstrual and once during the follicular phase. By use of a connectivity analysis we found that the inhibitory influence of left-hemispheric language areas on homotopic areas of the right hemisphere is strongest during the menses, resulting in a pronounced lateralization. During the follicular phase, due to rising estradiol levels, inhibition and thus functional cerebral asymmetries are reduced. These results reveal a powerful neuromodulatory action of estradiol 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.

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.

Estrogen replacement therapy induces functional asymmetry on an odor memory/discrimination test

The secondary afferents of the olfactory system largely project to the ipsilateral cortex without synapsing in the thalamus, making unilateral olfactory testing a useful probe of ipsilateral hemispheric activity. In light of evidence that lateralized performance on some perceptual tasks may be influenced by estrogen, we assessed left:right nostril differences in two measures of olfactory function in 14 post-menopausal women receiving estrogen replacement therapy (ERT) and 48 post-menopausal women receiving no such therapy. Relative to women not taking ERT, those receiving ERT exhibited better performance in the left nostril and poorer performance in the right nostril on an odor memory/discrimination test. Similar laterality effects were not observed for an odor detection threshold test employing phenyl ethyl alcohol. These results suggest that estrogen influences the lateralization of an odor memory/discrimination task and that hormone replacement therapy in the menopause may be an excellent paradigm for understanding lateralizing effects of hormones on some sensory processes.

The functional anatomy of semantic retrieval is influenced by gender, menstrual cycle, and sex hormones

This study examines the neurobiology of semantic retrieval and describes the influence of gender, menstrual cycle, and sex hormones on semantic networks. Healthy right-handed subjects (12 men, 12 women) were investigated with 3T-fMRI during synonym generation. Behavioral performance and sex hormone levels were assessed. Women were examined during the early follicular and midluteal cycle phase. The activation pattern in all groups involved left frontal and temporal as well as bilateral medial frontal, cingulate, occipital, basal ganglia, and cerebellar regions. Men showed greater left frontal activation than women in both menstrual cycle phases. Women yielded high correlations of left prefrontal activation with estradiol in the midluteal phase and with progesterone in both phases. Testosterone levels correlated highly with left prefrontal activation in all three groups. In all, we describe a cerebral network involved in semantic processing and demonstrate that it is significantly affected by gender and sex steroid hormones.

A comparative analysis of functional cerebral asymmetry in lesbian women, heterosexual women, and heterosexual men

This study tested dichotic listening performance, a measure of functional cerebral asymmetry previously shown to be sexually dimorphic, in homosexual women (n=23), heterosexual women (n=27), and heterosexual men (n=24). All participants completed a verbal consonant-vowel dichotic listening task. On three laterality indices, heterosexual men displayed a significantly greater right-ear advantage compared to heterosexual women only. Homosexual women did not differ significantly from heterosexual men or from heterosexual women. Post-hoc comparisons (with a statistical correction) for each ear separately showed that heterosexual men displayed significantly greater right-ear scores compared to heterosexual women only. These data suggest that lesbian women are somewhat masculinized in their functional cerebral asymmetry. The results were interpreted in the context of sexual variation in models of linguistic hemispheric processing.

Priming vs. rhyming: orthographic and phonological representations in the left and right hemispheres

The right cerebral hemisphere has long been argued to lack phonological processing capacity. Recently, however, a sex difference in the cortical representation of phonology has been proposed, suggesting discrete left hemisphere lateralization in males and more distributed, bilateral representation of function in females. To evaluate this hypothesis and shed light on sex differences in the phonological processing capabilities of the left and right hemispheres, we conducted two experiments. Experiment 1 assessed phonological activation implicitly (masked homophone priming), testing 52 (M=25, F=27; mean age 19.23years, SD 1.64years) strongly right-handed participants. Experiment 2 subsequently assessed the explicit recruitment of phonology (rhyme judgement), testing 50 (M=25, F=25; mean age 19.67years, SD 2.05years) strongly right-handed participants. In both experiments the orthographic overlap between stimulus pairs was strictly controlled using DICE [Brew, C., & McKelvie, D. (1996). Word-pair extraction for lexicography. In K. Oflazer & H. Somers (Eds.), Proceedings of the second international conference on new methods in language processing (pp. 45-55). Ankara: VCH], such that pairs shared (a) high orthographic and phonological similarity (e.g., not-KNOT); (b) high orthographic and low phonological similarity (e.g., pint-HINT); (c) low orthographic and high phonological similarity (e.g., use-EWES); or (d) low orthographic and low phonological similarity (e.g., kind-DONE). As anticipated, high orthographic similarity facilitated both left and right hemisphere performance, whereas the left hemisphere showed greater facility when phonological similarity was high. This difference in hemispheric processing of phonological representations was especially pronounced in males, whereas female performance was far less sensitive to visual field of presentation across both implicit and explicit phonological tasks. As such, the findings offer behavioural evidence indicating that though both hemispheres are capable of orthographic analysis, phonological processing is discretely lateralised to the left hemisphere in males, but available in both the left and right hemisphere in females.

Schizotypy and pseudoneglect: a critical update on theories of hemispheric asymmetries

INTRODUCTION

Positive schizotypy has been associated with a leftward spatial bias (pseudoneglect) in different tasks and populations. We tested whether this relationship (1) can be observed for two different hemispatial tasks in the same participants, and (2) is specific to positive schizotypy.

METHODS

Forty right-handed men performed a conventional line bisection task and a whole-body movement task. In the latter task, participants were presented with illuminated target locations on the floor, and had to visit the remembered locations (equal number in right and left hemispace) after a short time interval. We assessed side preferences in both tasks. Positive schizotypy, negative schizotypy, and cognitive disorganisation were assessed with a validated self-report questionnaire.

RESULTS

Irrespective of schizotypy, pseudoneglect was observed in both tasks. We found a rightward bisection and walking bias as a function of positive schizotypy, and also as a function of cognitive disorganisation for walking initiation.

DISCUSSION

This unexpected finding resulted in a review of hemispheric asymmetry for function in schizotypy, and in the discussion of potential variables that might account for the present discrepancy. We suggest that different schizotypy questionnaires and their presentation mode might be a potential contributor to the opposite findings in the literature.

In your right mind: right hemisphere contributions to language processing and production

The verbal/nonverbal account of left and right hemisphere functionality is the prevailing dichotomy describing the cerebral lateralization of function. Yet the fact that the left hemisphere is the superior language processor does not necessarily imply that the right hemisphere is completely lacking linguistic ability. This paper reviews the growing body of research demonstrating that, far from being nonverbal, the right hemisphere has significant language processing strength. From prosodic and paralinguistic aspects of speech production, reception, and interpretation, to prelexical, lexical and postlexical components of visual word recognition; strong involvement of the right hemisphere is implicated. The evidence reviewed challenges the notion that language is solely a function of the "verbal" left hemisphere, indicating that the right cerebral hemisphere makes significant and meaningful contributions to normal language processing as well.

Facial symmetry detection ability changes across the menstrual cycle

The effects of menstrual cycle phase and hormones on women's visual ability to detect symmetry and visual preference for symmetry were examined. Participants completed tests of symmetry detection and preference for male facial symmetry at two of three menstrual cycle phases (menses, periovulatory, and luteal). Women were better at detecting facial symmetry during the menses than luteal phase of their cycle. A trend indicated the opposite pattern for dot symmetry detection. Similarly, change in salivary progesterone levels across the cycle was negatively related to change in facial symmetry detection scores. However, there was no clear evidence of a greater preference for facial symmetry at any cycle phase, despite an overall preference for facial symmetry across phases. These findings suggest a menses phase advantage and a low progesterone advantage in women's ability to detect facial symmetry. The results are discussed in the context of hormonal, evolutionary mate selection, and functional neurocognitive theories.

Neural correlates of spatial frequency processing: A neuropsychological approach

We examined the neural correlates of spatial frequency (SF) processing through a gender and neuropsychological approach, using a recognition task of filtered (either in low spatial frequencies/LSF or high spatial frequencies/HSF) natural scene images. Experiment 1 provides evidence for hemispheric specialization in SF processing in men (the right hemisphere is predominantly involved in LSF analysis and the left in HSF analysis) but not in women. Experiment 2 aims to investigate the role of the right occipito-temporal cortex in LSF processing with a neurological female patient who had a focal lesion of this region due to an embolization of an arterioveinous malformation. This study was conducted 1 week before and 6 months after the surgical intervention. As expected, after the embolization, LSF scene recognition was more impaired than HSF scene recognition. These data support the hypothesis that the right occipito-temporal cortex might be preferentially specialized for LSF information processing and more generally suggest a hemispheric specialization in SF processing in females, although it is difficult to demonstrate in healthy women.

Sex hormonal modulation of hemispheric asymmetries in the attentional blink

The present study examines differences in functional cerebral asymmetries modulated by gonadal steroid hormones during the menstrual cycle in women. Twenty-one right-handed women with regular menstrual cycles performed a double-stream rapid serial visual presentation (RSVP) task, with one stream in each visual field, during the low steroid menses and the high steroid midluteal phase. They were required to detect a target item, and then a probe item, each of which could appear in either stream. If the probe item appeared 200 ms after the target, detection of the probe was impaired-a phenomenon known as the "attentional blink." This occurred in both streams in the midluteal phase, but only in the right visual field during menses. Thus low steroid levels appeared to restrict the attentional blink to the left hemisphere, while high levels of estradiol and progesterone in the midluteal phase appeared to reduce functional asymmetries by selectively increasing the attentional blink in the right hemisphere. This effect appears to be mediated by estradiol rather than progesterone, and it is compatible with the assumption of a hormone-related suppression of right hemisphere functions during the midluteal phase.

Age-related changes in hemispheric asymmetry depend on sex

A total of 92 participants, 50 younger (mean age 26.3 years) and 42 older (mean age 63.8 years), were tested for visual-field asymmetries. On a word-matching task, a right-visual-field (RVF) advantage increased with age, consistent with the theory that right-hemispheric function shows relatively greater decline with age than left-hemispheric function. On a figural-comparison task, a left-visual-field (LVF) advantage was marginally decreased with age in the men, but significantly increased in the women, probably because age-related changes in hormonal levels are more pronounced in women. This increase in LVF advantage is contrary to both the HAROLD theory that hemispheric asymmetry declines with age, and the theory of relative right-hemispheric decline.

Brain State-dependent Functional Hemispheric Specialization in Men but not in Women

Hemispheric specialization is reliably demonstrated in patients with unilateral lesions or disconnected hemispheres, but is inconsistent in healthy populations. The reason for this paradox is unclear. We propose that functional hemispheric specialization in healthy participants depends upon functional brain states at stimulus arrival (FBS). Brain activity was recorded from 123 surface electrodes while 22 participants (11 women) performed lateralized lexical decisions (left hemisphere processing) on neutral and emotional (right hemisphere processing) words. We determined two classes of stable FBS, one with right anterior-left posterior orientations (RA-LP maps) and one with left anterior-right posterior orientations (LA-RP maps). Results show that functional hemispheric specialization is dependent upon the class of FBS and gender. Of those with LA-RP maps, only men showed a strong emotional word advantage (EWA) after left visual field (right hemisphere) presentation, but no EWA after right visual field (left hemisphere) presentation. Subsequent to all other brain states, there was an almost equal EWA after presentation to either visual field. Only about half of the FBS in men led to the pattern of functional hemispheric specialization. We suggest that 'split-brain' research may be marginally describable by a model, but only in exceptional situations, while in connected brains this functional hemispheric specialization is only one of many dynamic states.

Increased cortisol and decreased right ear advantage (REA) in dichotic listening following a negative mood induction

This study aimed to evaluate neuroendocrine responses and changes in perceptual asymmetry following an induced negative affect. Cortisol increasing in response to negative affect has been reported, while current brain models of emotion processing link negative affect to the right hemisphere. In this study, the Velten Mood Induction Procedure was used to generate neutral or negative affect in 44 healthy subjects. The PANAS scales were used to assess self-reported mood. A consonant-vowel dichotic listening (DL) test was applied after the neutral and negative affect inductions, and levels of salivary cortisol were determined by radioimmunoassay. For the negative affect condition, and congruent with the hypothesis tested, PANAS positive scores diminished (p<0.001) and PANAS negative scores increased (p<0.001), yielding an inverse correlation between them. A significant increase in cortisol levels was also seen (p<0.04). When taking cortisol reactivity into account, PANAS negative scores were higher for high-than for low-cortisol responders (p<0.02). Regarding DL, an increase in left ear items (p<0.04) and a decrease in right ear items (p<0.03) reported for those subjects who obtained a right ear advantage in the neutral condition. An explanation in terms of Kinsbourne's model for attentional-activation influences on DL is postulated and implications for the issue of affective illness are also discussed.

Hemispheric asymmetry in spatial attention across the menstrual cycle

Functional cerebral asymmetries (FCAs) are known to fluctuate across the menstrual cycle. The mechanisms of these sex hormonal modulations are poorly understood. It has been suggested that gonadal steroid hormones might suppress or specifically activate one hemisphere. However, recent studies suggest that high levels of gonadal steroid hormones reduce FCAs by its modulating effects on cortico-cortical transmission. To investigate the activating effects of gonadal steroid hormones on the interhemispheric interaction, a visual line-bisection task was administered to normally cycling women during menses and the midluteal cycle phase as well as to similar-aged healthy men. The results replicate previous findings of a sex difference in line-bisection as a function of hand-use and show that the hand-use effect fluctuates across the menstrual cycle. High levels of estradiol during the midluteal phase were related to a decrease of the hand-use effect. It is concluded that cycle-related fluctuations in levels of gonadal steroid hormones affect hemispheric asymmetry of spatial attention, presumably by interhemispheric spreading of neuronal activation.

Performance in a test demanding prefrontal functions is favored by early luteal phase progesterone: an electroencephalographic study

There are some psychological studies showing changes in intellectual efficiency before and during menstruation. Many women report that they experience a feeling of difficulty to initiate activities, confront challenging situations and lack of concentration suggesting transient changes in frontal lobe functions related with gonadal hormone levels. Therefore, performance of a task demanding prefrontal functions, the Wisconsin Card Sorting Test, with simultaneous recording of electroencephalographic (EEG) activity was assessed in 9 healthy women, in a repeated measure study, during ovulation (OVU), early luteal (EL), late luteal (LL) and menstrual (MEN) phases. Spectral power of base line and task EEG, and number of responses to reach successful and unsuccessful outcomes in the task were evaluated. Performance was impaired to a certain degree during the OVU phase and was associated with an attenuated alpha1 power and with an increase of the theta and beta2 power. Performance was better during EL phase, when progesterone level is at its highest, no significant changes were observed from BL to task. Performance was worse during LL phase when hormone levels are at its lowest and was associated with a decrease in beta1 and beta2 power together with a significant attenuation of alpha1 and alpha2 power. During MEN phase performance was also improved and was associated with a significant decrease of alpha1 and alpha2 power and no changes in beta power were observed. These findings show that performance of a task demanding internal attention and planning is modulated by physiological progesterone and estrogen levels during menstrual cycle and is associated with specific EEG profiles.

Electrical neuroimaging reveals early generator modulation to emotional words

Functional electrical neuroimaging investigated incidental emotional word processing. Previous research suggests that the brain may differentially respond to the emotional content of linguistic stimuli pre-lexically (i.e., before distinguishing that these stimuli are words). We investigated the spatiotemporal brain mechanisms of this apparent paradox and in particular whether the initial differentiation of emotional stimuli is marked by different brain generator configurations using high-density, event-related potentials. Such would support the existence of specific cerebral resources dedicated to emotional word processing. A related issue concerns the possibility of right-hemispheric specialization in the processing of emotional stimuli. Thirteen healthy men performed a go/no-go lexical decision task with bilateral word/non-word or non-word/non-word stimulus pairs. Words included equal numbers of neutral and emotional stimuli, but subjects made no explicit discrimination along this dimension. Emotional words appearing in the right visual field (ERVF) yielded the best overall performance, although the difference between emotional and neutral words was larger for left than for right visual field presentations. Electrophysiologically, ERVF presentations were distinguished from all other conditions over the 100-140 ms period by a distinct scalp topography, indicative of different intracranial generator configurations. A distributed linear source estimation (LAURA) of this distinct scalp potential field revealed bilateral lateral-occipital sources with a right hemisphere current density maximum. These data support the existence of a specialized brain network triggered by the emotional connotation of words at a very early processing stage.