Sex differences in EEG power changes in retention of dichotically and monaurally presented verbal stimuli

EEG power mapping was used to study gender differences in hemispheric functional organization during memorizing dichotically and monaurally presented verbal information. Right-handed students (12 men and 14 women) participated in experiments. The EEG was recorded from 16 electrodes placed at homologous sites of the left and right brain hemispheres. Task-related changes in the thetal power in men differentiated between monaural presentations to different ears, i.e., situations of oppositely directed attention. In women the thetal power reactivity (the difference between the band power logarithms under baseline conditions and in task interval) differentiated between dichotic and monaural presentations of words, i.e., situations with different memory loads. Gender differences were also found in the alpha frequency band. Power changes in the alpha 1 band in all memory tasks and power changes in the alpha 2 were more evident in the right hemisphere in men but in the left hemisphere in women. In contrast, in the posterior temporal lead the alpha 2 power reactivity in men was higher in the right hemisphere, whereas in women the lateral differences were absent. As compared to men, the alpha 2 desynchronization in women was also more pronounced in posterior regions of both hemispheres. There were no gender differences in efficacy of memorizing. It is suggested that different processing strategies rather than different behavioral performance may be responsible for the revealed specific spatiotemporal EEG patterns.     

The study of interhemispheric asymmetry in spatial-perceptive problem solving

Features of brain interhemispheric asymmetry during solving the spatial figurative task (maze model) were studied in men and women with different intelligence quotients (IQ). It was shown that during task solving the rate of information processing was higher in the right brain hemisphere, and amplitude characteristics of the event-related potentials were higher in the left hemisphere. No gender and IQ differences in the character of interhemispheric interaction were found during the realization of the maze-model task. The results testify that the character of hemispheric interaction depends om the task rype rather than gender and intelligence level.     

Role of the Brainstem Reticular Formation in the Mechanisms of Cortical Electrogenesis

In rats, we studied peculiarities of the electrocorticogram (ECoG) and its segments characterized by synchronization and desynchronization phenomena; these periods were differentiated using a segmentation procedure. The electrocorticogram was recorded under conditions of the intact brain (IB) and in animals with the isolated forebrain (IFB) using intercollicular transection. When ECoG was recorded from IFB preparations, it differed from ECoG of the IB in decreased amplitudes of the rhythms and their reorganization with shifts of the frequency characteristics toward lower values, as well as in greater amplitudes of ECoG rhythms in the left hemisphere (lateralization of the ECoG activity toward this hemisphere). Significant differences of the indices of functional asymmetry were observed in the two examined experimental situations. Using calculations of multiple linear regression and subsequent visualization of the results using polycyclic multigraphs, we found a clear specificity in the formation of correlation links between the amplitudes of different ECoG rhythms under conditions of the IB and IFB preparation. We discuss the role of the brainstem structures, in particular that of the reticular formation, in the organization of integral ECoG activity and the possible importance of mutual influences between hypothetical generators of the ECoG rhythmus for this organization.Neirofiziologiya/Neurophysiology, Vol. 37, No. 1, pp. 39–51, January–February, 2005.     

A correlation between the efficiency of probabilistic prediction and characteristics of left and right interhemispheric activation

The interhemispheric difference in the level of EEG activation was studied as a correlate of the efficiency of human probabilistic activity. The interhemispheric asymmetry of the arousal duration in the projection (occipital) and associative (central) areas was assessed in two tested groups of subjects: with an adequate prediction and difficulties in predictive activity under conditions of different information significance of a stimulus. Under conditions of relevant stimulation, the asymmetry coefficient was higher, and the desynchronization reaction in the central areas of the left hemisphere was considerably shorter in bad predictors than in good ones. It is suggested that the asymmetry observed in bad predictors is determined by a nonspecific activation of subcortical structures, and in good predictors the asymmetry is related with the local neocortical activation.     

Sex-Differences of Face Coding: Evidence from Larger Right Hemispheric M170 in Men and Dipole Source Modelling

The processing of faces relies on a specialized neural system comprising bilateral cortical structures with a dominance of the right hemisphere. However, due to inconsistencies of earlier findings as well as more recent results such functional lateralization has become a topic of discussion. In particular, studies employing behavioural tasks and electrophysiological methods indicate a dominance of the right hemisphere during face perception only in men whereas women exhibit symmetric and bilateral face processing. The aim of this study was to further investigate such sex differences in hemispheric processing of personally familiar and opposite-sex faces using whole-head magnetoencephalography (MEG). We found a right-lateralized M170-component in occipito-temporal sensor clusters in men as opposed to a bilateral response in women. Furthermore, the same pattern was obtained in performing dipole localization and determining dipole strength in the M170-timewindow. These results suggest asymmetric involvement of face-responsive neural structures in men and allow to ascribe this asymmetry to the fusiform gyrus. This specifies findings from previous investigations employing event-related potentials (ERP) and LORETA reconstruction methods yielding rather extended bilateral activations showing left asymmetry in women and right lateralization in men. We discuss our finding of an asymmetric fusiform activation pattern in men in terms of holistic face processing during face evaluation and sex differences with regard to visual strategies in general and interest for opposite faces in special. Taken together the pattern of hemispheric specialization observed here yields new insights into sex differences in face perception and entails further questions about interactions between biological sex, psychological gender and influences that might be stimulus-driven or task dependent.     

Effects of weak microwave fields amplitude modulated at ELF on EEG of symmetric brain areas in rats

Averaged electroencephalogram (EEG) frequency spectra were studied in eight unanesthetized and unmyorelaxed adult male rats with chronically implanted carbon electrodes in symmetrical somesthetic areas when a weak (0.1–0.2 mW/cm) microwave (MW, 945 MHz) field, amplitude-modulated at extremely low frequency (ELF) (4 Hz), was applied. Intermittent (1 min “On,” 1 min “Off”) field exposure (10-min duration) was used. Hemispheric asymmetry in frequency spectra (averaged data for 10 or 1 min) of an ongoing EEG was characterized by a power decrease in the 1.5–3 Hz range on the left hemisphere and by a power decrease in the 10–14 and 20–30 Hz ranges on the right hemisphere. No differences between control and exposure experiments were shown under these routines of data averaging. Significant elevations of EEG asymmetry in 10–14 Hz range were observed during the first 20 s after four from five onsets of the MW field, when averaged spectra were obtained for every 10 s. Under neither control nor pre- and postexposure conditions was this effect observed. These results are discussed with respect to interaction of MW fields with the EEG generators. Bioelectromagnetics 18:293–298, 1997. © 1997 Wiley-Liss, Inc.     

The hemispheric lateralization of the recognition of noisy visual stimuli in man

At tachistoscopic unilateral presentation of noisy visual stimuli and application of "yes-no" method in man predominance was found of the right hemisphere by the number and "yes" reaction time and of the left hemisphere by the number of responses "no". At verbal mnemic load preceding the presentation of visual patterns the left hemisphere asymmetry was observed by the number of "yes" responses and reactions time of both types. FMA was more clearly expressed in men in the first case and in women--in the second one. In more difficult conditions of recognition of several types of patterns, FMA was noticed mainly in women: initial left hemisphere advantage during the increase of the disturbance was changed to the right hemispheric one and appeared again. Preferential participation of the right hemisphere in singling out of the visual signal from noise is supposed. Possibility of the left hemispheric asymmetry manifestation was determined by the specificity and complexity of the visual task, by the level of the disturbance, presentation of competitive task and sexual composition of the group.     

Hemispheric participation in the shaping of spatial-motor asymmetry in visual recognition in rats

Asymmetry of movement direction was found in Wistar rats at establishing of motor alimentary conditioned reflex to simultaneously presented visual stimuli. In the course of learning the asymmetry weakened on the whole, but some individuals retained right- or left side preference. The analysis of asymmetry change before and after unilateral cortical inactivation revealed a special role of right hemisphere influences for the formation of right-side preference and of the left hemisphere--for the choice of the left direction. The lack of asymmetry was observed at the presence of the influences from the left hemisphere cortex depressing ipsilateral nigro-striate system and activating the contralateral one. Influences of the cortex of both hemispheres reduce the absolute value of the asymmetry coefficient; the left hemisphere has a special significance for manifestation of temporal asymmetry parameters. Photic interference is a factor modulating the asymmetry. It reduces the right hemisphere activity more than that of the left one; it intensifies right hemisphere influences, contributes to the involvement of the transcallosal conduction channel in the formation of spatial-motor asymmetry.     

Resonance phenomena to rhythmic light stimulation with various intensity and frequency in human EEG

The photoinduced resonance EEG response in the occipital area (O1 and O2) of right-handed men during 12-s intermittent photic stimulation was studied as a function of flash frequency (6, 10, or 16 Hz) and intensity (5 levels from 0.05 to 0.7 J). The EEG power in the narrow band coinciding with stimulation frequency was FFT-extracted in 3-s intervals before, during, and after each stimulation. It was found that increase in flash intensity was accompanied by an enhancement of the resonance EEG response and decrease in time of reaching its maximal value. These changes were to a greater extent characteristic for the right hemisphere. The low-intensity stimulation induced more pronounced resonance effects in the left hemisphere, whereas the high-intensity flashes to a greater extent involved the right hemisphere. The asymmetry of the EEG response to stimulation of the middle intensity was slight, and the time of reaching the maximal level of the resonance activation was about 6-8 s. A relatively high level of the resonance EEG response was observed during stimulation with the frequency of 10 Hz, even in case of its minimal intensity. The most pronounced resonance EEG response was induced in the right occipital area by the high-intensity 16-Hz stimulation. The enhanced sensitivity of the right hemisphere to intensity of flashes is interpreted as an indication of interhemispheric differences in nonspecific adaptive mechanisms of the brain.     

Ontogenetic aspects of individual characteristics of functional brain asymmetry in the perception of emotions

Studies have been made on individual variations in perception of speech emotional information by 7-16-year children. Significant differences between subjects from various age groups were found concerning the correct recognition of emotions, the degree of brain asymmetry and domination type. The exactness of emotional recognition increases with age, while the degree of asymmetry becomes lower, the right hemisphere domination becoming more stable in processing of speech emotional information. With age, individual type of asymmetry turns to the specific one, reflecting asymmetry formation during evolution.     

The effect of sex steroid hormones on interhemispheric asymmetry in rats]

The effect of gonadectomy and sex-steroid hormones treatment on functional interhemispheric asymmetry to the reaction of pain cry avoidance of another species (emotional reactions) and motor and exploratory activity of open-field behavior in Wistar rats of 3 months old has been investigated. A spreading depression technique for hemisphere inactivation has been used. The hemispheric asymmetry of the reactions in intact rats was characterized by sex dimorphism; the left hemisphere dominated to a great extent in males than in females under the control of emotional reactions; in motor and exploratory activity in open-field behavior of rats the left hemisphere dominated in males and the right one--in female. In both sexes the neonatal gonadectomy levelled the interhemispheric differences in reactions under investigation. The following treatment of females with estradiol and males with testosterone didn't restore the asymmetry. After the castration at the age of 3 months the correlation between the size and direction of interhemispheric differences became reverse. The treatment of females with testosterone and males with estradiol both castrated in adulthood restored the interhemispheric asymmetry in males and had no effect in females. The treatment of intact rats with hormones of opposite sex led to the enhancement of left hemisphere dominance in motor and exploratory activity in males and levelled the asymmetry in females. It has been shown that in adult rats sex-steroids effect predominantly the right hemisphere.     

EEG characteristics of bioelectrical activity of the brain in women with normal and complicated pregnancy

Spectrum and coherent EEG analysis has been made at 109 pregnant women during 35-36 weeks of gestation. It has been shown, that functional interhemispherical asymmetry of the brain is the sensible parameter of normal and complicated gestation. It has been found out that as for normal pregnancy prevailing activation in central and temple areas of the brain contralateral to the side of placenta placement in uterus is characteristic. The development of gestation complications accompanied by the inversion of interhemispherical asymmetry of EEG activation. It was pointed out that correlative relations of bioelectrical activity of the brain in women with normal gestation are the indicator of dominating of nervous centers of left hemisphere in the integrational process.     

Specificity of Auditory Cognitive Evoked Potentials in Musicians

We measured characteristics of evoked potentials, EPs, developing after presentation of significant tonal acoustic stimuli in subjects systematically engaged in music training (n = 7) and those having no corresponding experience (n = 10). The peak latencies of the P3 component in the left hemisphere of musicians were significantly shorter than those in non-musicians (on average, 279.9 and 310.2 msec, respectively). Musicians demonstrated no interhemisphere differences of the latencies of components N2, P3, and N3, while a trend toward asymmetry was obvious in non-musicians (the above components were generated somewhat later in the left hemisphere). The amplitudes of EP components demonstrated no significant intergroup differences, but the amplitude of the P3 wave was higher in the left hemisphere of non-musicians than that in the right hemisphere. Possible neurophysiological correlates of the observed specificity of EPs in the examined groups are discussed.     

Hemisphere asymmetry of motor-feeding behavior of mice in a multi-alternative symmetrical maze

The behaviour of mice of BALB/c line was studied in a symmetrical multialternative Y-maze: their motor, alimentary and investigating activities as well as spatial-motor asymmetry. In animals with inactivated left hemisphere, as compared to intact ones, the motor and alimentary activities were lowered, and the investigating one augmented. Instead of the weak left-side asymmetry a distinct left-side preference appeared of most Y-maze sections, and right-side preference for approaches to the feeders. Elimination of the right hemisphere did not change the motor activity; the alimentary one decreased and the investigating one augmented, but less than during inactivation of the left hemisphere. On the whole, the right-side asymmetry appeared for all sections. According to all parameters studied, the influence of the left hemisphere on animal behaviour was more expressive and diverse. Spatial preference is formed with participation of influences of both hemispheres. The differences between them are more qualitative than quantitative.     

Asymmetry of the transcallosal responses in the parietal cortex of kittens in the 1st month of life

In acute experiments on kittens the process of formation of asymmetry of transcallosal responses (TCR) was studied in multiple leads from symmetrical points of the parietal cortex. By the early positive-negative TCR complex, vanishing as a result of callosotomy, predominance of positive components in the right hemisphere was found in 2-7 days kittens, whereas in 8-24 days animals the left hemisphere dominated by both phases of responses. By the late TCR component preserved after section of the callosal body, left-hemispheric asymmetry was found in the elder group of kittens; it was absent in the younger animals. TCR asymmetry in the parietal cortex depended on the sex of the animals. With their age its inversion and enhancement took place. This process is based on the increase of TCR amplitude in the left hemisphere, with no increase in the right hemisphere.     

Climatic drivers of hemispheric asymmetry in global patterns of ant species richness

Although many taxa show a latitudinal gradient in richness, the relationship between latitude and species richness is often asymmetrical between the northern and southern hemispheres. Here we examine the latitudinal pattern of species richness across 1003 local ant assemblages. We find latitudinal asymmetry, with southern hemisphere sites being more diverse than northern hemisphere sites. Most of this asymmetry could be explained statistically by differences in contemporary climate. Local ant species richness was positively associated with temperature, but negatively (although weakly) associated with temperature range and precipitation. After contemporary climate was accounted for, a modest difference in diversity between hemispheres persisted, suggesting that factors other than contemporary climate contributed to the hemispherical asymmetry. The most parsimonious explanation for this remaining asymmetry is that greater climate change since the Eocene in the northern than in the southern hemisphere has led to more extinctions in the northern hemisphere with consequent effects on local ant species richness.     

Interhemisphere asymmetry of the CSF dynamics and biomechanical properties of the skull

This investigation shows that both intracranial liquor circulation and skull biomechanical properties evaluated by its pliability (compliance) to intracranial pressure are characterised by marked interhemisphere asymmetry. The interhemisphere differences of cerebrospinal fluid mobility were evaluated by means of asymmetry coefficient (right/left ratio of liquor mobility) which was found to be 1.25-1.45 in healthy middle-age persons. For the skull pliability (compliance) the coefficient of hemispheric asymmetry was 0.75-0.95. These two hemisphere asymmetry coefficients are characterized by reciprocal relationships. These coefficients demonstrated no dominancy related to right/left hemisphere as well as no correlation with neurophysiological parameter. Functional tests (apnoea, hyperventilation, Stookey test) gave rise to significant changes of these coefficient values. At ageing, the magnitudes of these coefficients decreased. The spectral analysis of pulse waves of dopplerogram and rheoencephalogram reveals hemisphere asymmetry, too. It should be suggested that the interhemisphere asymmetry of the CSF dynamics and skull biomechanical properties is a special mechanism which contributes in the process of circulatory-metabolic support of brain activity.     

Face Coding Is Bilateral in the Female Brain

Background

It is currently believed that face processing predominantly activates the right hemisphere in humans, but available literature is very inconsistent.

Methodology/Principal Findings

In this study, ERPs were recorded in 50 right-handed women and men in response to 390 faces (of different age and sex), and 130 technological objects. Results showed no sex difference in the amplitude of N170 to objects; a much larger face-specific response over the right hemisphere in men, and a bilateral response in women; a lack of face-age coding effect over the left hemisphere in men, with no differences in N170 to faces as a function of age; a significant bilateral face-age coding effect in women.

Conclusions/Significance

LORETA reconstruction showed a significant left and right asymmetry in the activation of the fusiform gyrus (BA19), in women and men, respectively. The present data reveal a lesser degree of lateralization of brain functions related to face coding in women than men. In this light, they may provide an explanation of the inconsistencies in the available literature concerning the asymmetric activity of left and right occipito-temporal cortices devoted to face perception during processing of face identity, structure, familiarity or affective content.     

Hemispheric asymmetry of the nigrostriatal system of the brain in rats genetically predisposed to catalepsy]

Hemispheric asymmetry of nigro-striate system in a strain of rats GC bred from Wistar for a predisposition to cataleptic reaction was studied by means of biochemical and morphological methods. Hemispheric asymmetry was found in GC and Wistar rats with respect to aminopeptidase activity in neurons of caudate nucleus, with a more pronounced left-side increase in GC rats, the asymmetry index being 13.7%. Acetylcholine esterase activity in subcellular particles of caudate nucleus showed an inversion of asymmetry with higher activity in the left hemisphere of Wistar and right hemisphere of GC rats, and asymmetry index of 15.5%. With respect to the number of astroglia cells in S. nigra, and astroglia and oligodendroglia in N. accumbens there was also an inversion of asymmetry in GC rats who had more cells in the structures of the left hemisphere, whereas Wistar rats had more in the right hemisphere. The asymmetry index was high and equal to 29.8% for astroglia in S. nigra, and 17% for astroglia and 21.4% for oligodendroglia in N. accumbens. However, in S. nigra the number of neurons and oligodendroglia cells was equally increased in the right hemisphere in GC and Wistar rats. The data suggest that the mechanism of hereditary pathology of brain nigro-striate system involves both enhancement and inversion of the hemispheric asymmetry.