Spatial abilities, sex differences and EEG functioning

Testosterone and the Brain: From Cognition to Autism

Sex and gender matter in all aspects of life. Humans exhibit sexual dimorphism in anatomy, physiology, but also pathology. Many of the differences are due to sex chromosomes and, thus, genetics, other due to endocrine factors such as sex hormones, some are of social origin. Over the past decades, huge number of scientific studies have revealed striking sex differences of the human brain with remarkable behavioral and cognitive consequences. Prenatal and postnatal testosterone influence brain structures and functions, respectively. Cognitive sex differences include especially certain spatial and language tasks, but they also affect many other aspects of the neurotypical brain. Sex differences of the brain are also relevant for the pathogenesis of neuropsychiatric disorders such as autism spectrum disorders, which are much more prevalent in the male population. Structural dimorphism in the human brain was well-described, but recent controversies now question its importance. On the other hand, solid evidence exists regarding gender differences in several brain functions. This review tries to summarize the current understanding of the complexity of the effects of testosterone on brain with special focus on their role in the known sex differences in healthy individuals and people in the autism spectrum.

Sex and Ability Differences in Neural Strategy for Piaget’s Water Level Test

To explore brain activation differences between the sexes and between high and low performers on spatial perception performance, 43 college students (20 males and 23 females) performed the Piaget’s Water Level Test (WLT) while their electroencephalogram signals were recorded. A 2 (Sex) × 2 (Group: high performing vs. low performing) × 2 (Hemisphere: left vs. right) × 3 (Region: frontal, parietal, and temporal) mixed analysis of variance on beta power data showed that females more significantly activated the left hemisphere when performing the WLT, suggesting their application of an analytic strategy. In contrast, males showed a bilateral activation pattern, suggesting their use of an analytic- or holistic-combined strategy. Moreover, superior performance on the WLT was associated with enhanced temporal lobe functioning, suggesting that a superior analytic skill is key to successful performance on the WLT. There is likely modulating impact of both cognitive style and specific task properties on spatial perception strategy preferences.

Frontal and Posterior Erps Related to Line Bisection

The aim of this study was to investigate the dynamic nature of the cortical visuospatial attention processes during the line bisection test, which is sensitive to perceptual asymmetries. EEGs of 26 normal volunteers were recorded during the administration of a computerized line bisection test, which requires participants mark the midline of lines using a mouse. Two event-related potentials subsequent and time locked to the line presentations, namely, P300 and a positive slow wave, were obtained. Findings suggested that both potentials were related to the test performance, and the right hemisphere was more active. Analysis suggested a right parietotemporal and superior parietal locus for the P300 and right prefrontal activity for the positive slow wave. A dynamic asymmetrical activity was identified, such that after primary visual perception, spatial processing is then initiated in the right parietotemporal cortex and then proceeds to the right prefrontal cortex.

Sex differences in mathematical reasoning ability in intellectually talented preadolescents: Their nature, effects, and possible causes

Several hundred thousand intellectually talented 12-to 13-year-olds have been tested nationwide over the past 16 years with the mathematics and verbal sections of the Scholastic Aptitude Test (SAT). Although no sex differences in verbal ability have been found, there have been consistent sex differences favoring males in mathematical reasoning ability, as measured by the mathematics section of the SAT (SAT-M). These differences are most pronounced at the highest levels of mathematical reasoning, they are stable over time, and they are observed in other countries as well. The sex difference in mathematical reasoning ability can predict subsequent sex differences in achievement in mathematics and science and is therefore of practical importance. To date a primarily environmental explanation for the difference in ability has not received support from the numerous studies conducted over many years by the staff of Study of Mathematically Precocious Youth (SMPY) and others. We have studied some of the classical environmental hypotheses: attitudes toward mathematics, perceived usefulness of mathematics, confidence, expectations/ encouragement from parents and others, sex-typing, and differential course-taking. In addition, several physiological correlates of extremely high mathematical reasoning ability have been identified (left-handedness, allergies, myopia, and perhaps bilateral representation of cognitive functions and prenatal hormonal exposure). It is therefore proposed that the sex difference in SAT-M scores among intellectually talented students, which may be related to greater male variability, results from both environmental and biological factors.

Maturation rate and spatial, verbal, and musical abilities: A seven-year-longitudinal study

We traced spatial, verbal and musical abilities through a seven-year period of adolescence. When we started our study, 60 boys had reached a mean age of 11.72, 60 girls were 11.52 on average. Menarche and mutation served as markers for maturation. We found that early, mid, and late maturers differed on spatial orientation and on tactile-visual discrimination as measured with the Witelson task. No differences between the maturational groups emerged on verbal fluency and on Wing's Standardized Tests of Musical Intelligence. At some stages, sex differences on spatial, verbal, and musical tests emerged, and disappeared at others. The sex differences in performance levels were not associated with a sex-specific relationship between maturation rate and performance levels. We found indications of the usefulness of sex hormone measurement in relation to cognitive and musical development in adolescence.

Within-subject reliability and inter-session stability of EEG power and coherent activity in women evaluated monthly over nine months

OBJECTIVE

Quantitative EEG parameters during resting conditions are used as baseline in research on cognition and in serial-EEG recordings. Despite its increasing use in cognitive research and the numerous evidences of the existence of sex differences in EEG, EEG stability has been mainly investigated in men. Particularly, studies on stability of coherent activity are scarce. The aim of this study was to investigate within-subject reliability and inter-session stability of resting EEG over a nine-month period in women.

METHODS

Within-subject reliability and inter-session stability were analyzed for absolute power and inter- and intrahemispheric coherent activity at central and posterior regions, once a month, in resting conditions, with eyes open and closed.

RESULTS

Within-subject reliability was very high (r>0.89) for all subjects and EEG parameters. Inter-session stability was higher with eyes closed and for interhemispheric coherent activity, and poorer with eyes open especially in the alpha band.

CONCLUSIONS

Present results indicate high reliability of the pattern of power and coherent activity of each individual woman during rest, and group stability of EEG activity with eyes closed at least over a nine-month period.

SIGNIFICANCE

These results provide information on EEG stability in women over a long period.

Interhemispheric asymmetry of EEG alpha activity at rest and during the Wisconsin Card Sorting Test: relations with performance

There are conflicting results regarding the functional asymmetry of the prefrontal cortex. Spectral power analysis of electroencephalographic (EEG) activity can provide important clues about the cortical mechanisms. In this study, interhemispheric EEG alpha power asymmetry of healthy individuals was investigated during the execution of the Wisconsin Card Sorting Test (WCST) and during rest. We analyzed alpha-1 (8.6-10.2 Hz) and alpha-2 (10.9-12.5 Hz) bands separately and found some evidence to indicate that lower and upper alpha bands reflect different cortical processes. On the other hand, greater alpha power during resting correlated with higher performance on the WCST. The lower left frontal alpha power during WCST correlated significantly with the higher WCST performance. However, greater bilateral parietal alpha power during WCST correlated with higher performance. Significant correlations between EEG activity and WCST performance were, in general, restricted to lower alpha power, both at rest and during the task. These findings are discussed with regard to attention processes reflected by lower alpha activity.

Sex differences on a mental rotation task: variations in electroencephalogram hemispheric activation between children and college students

The area of cognitive research that has produced the most consistent sex differences is spatial ability. In particular, men usually perform better on mental rotation tasks than women. Performance on mental rotation tasks has been associated with right parietal activation levels, both during task performance and prior to performance during baseline recordings. This study examined the relations among sex, age, electroencephalogram (EEG) hemispheric activation (at the 10.5 Hz to 13.5 Hz frequency band), and 2-D mental rotation task ability. Nineteen 8-year-olds (10 boys) and 20 college students (10 men) had EEG recorded at baseline and while performing a mental rotation task. Men had a faster reaction time on the mental rotation task than women, whereas there were no differences between boys and girls. After covarying for baseline EEG power values, men exhibited more activation (lower EEG power values) than women in the parietal and posterior temporal regions, whereas boys' and girls' power values did not differ in the parietal or posterior temporal regions. Furthermore, during the baseline condition, men generally exhibited more activation (lower EEG power values) throughout all regions of the scalp. Results support the hypothesis that a change that affects both brain activation and performance on mental rotation tasks occurs sometime between childhood and adulthood.

A lack of cerebral lateralization in schizophrenia is within the normal variation in brain maturation but indicates late, slow maturation

The planum temporale (PT) bias, PT leftward, PT symmetry, and PT rightward reversal and sidedness preference, consistent right-handedness, ambilaterality, and consistent left-handedness are placed on a continuum mirroring the normal variation in rate of brain maturation. Maturational rate declines as we pass from PT leftward bias and consistent right-handedness to PT reversal and consistent left-handedness. Concomitantly, we expect an increased prevalence of males due to their pubertal age being about 2 years later than that of females, and a shift in cognitive profile from higher verbal scores than performance scores on the WAIS to higher performance than verbal scores. Three disorders fulfilling the criteria of late CNS maturation apart from the corresponding cognitive profile were studied: infantile autism (IA), schizophrenia (S), and developmental dyslexia (DD). These disorders have in common deficits in cognition, perception, and somatomotor function. The deficits range from an arrest in brain development (which is evident in infancy superimposed on late maturation in IA) to overall delayed brain and somatic development in S (culminating in postpubertal psychotic episodes and persistent and generalized residual deficits). Finally, reading inability, problems in perception (vision and hearing) and in motor coordination, particularly between the two hemispheres, characterize DD. Enhancing brain maturation and the prevalence of 'normal' cerebral asymmetry--laterality is preferable if we want to reduce the risk of developing the above-mentioned disorders. It is suggested that in the past environmental challenges have favored early maturation, with its abundant neuronal population, arborization and excessive density of synapses and cerebral excitability which has powered evolution through the mechanism of natural selection. Early maturation is obtainable through optimal nutrition, including a satisfactory amount of marine fat (PUFA), before and during pregnancy and later in life.

Spatial ability and lateralization in the haptic modality

Two experiments examined the relation between spatial visualization ability and spatial lateralization using a unimanual haptic task with random shapes as stimuli. High spatial ability was not associated with enhanced right hemisphere functioning. However, spatial ability considered in the context of sex differences (Experiment 1) and level of verbal ability (Experiment 2) did yield interactions with the laterality (i.e., hand) variable, at least for first-list data. In Experiment 2, verbal ability also interacted with the gender and hand variables and in the same crossed ability-sex manner as was found for spatial ability in Experiment 1. It is concluded that cognitive abilities, including the relation between abilities, may be associated with the extent to which the right cerebral hemisphere mediates tactuospatial performance and that this association may differ for males and females.

Effect of spatial ability and sex on inter- and intrahemispheric correlation of EEG activity

Inter- and intrahemispheric correlation of the EEG activity at rest was computed in two groups of men and women, between 17 and 21 years old, with extreme degrees of spatial ability (SA) evaluated by the Spatial Relations Subtest of the Differential Aptitudes Test (DAT). Interhemispheric (INTERr) and intrahemispheric (INTRAr) EEG correlations were computed by means of Pearson product-moment coefficients for 5 EEG bands after digitally filtering with an FFT. Women showed significantly higher INTERr of alpha 1 between left and right centrals, lower INTRAr between right frontal and right central regions and lower INTRAr within the left than in the right hemisphere. High SA subjects showed lower INTERr between left and right frontal derivations and higher INTRAr between frontal and parietal and between central and parietal regions of both hemispheres. Sex interacted with SA in INTRAr of alpha between right frontal and right temporal regions with high SA women showing lower INTRAr than low SA women and than men. The present results indicate a different inter- and intrahemispheric functional organization in men and women and in subjects with high and low spatial ability.

Sex-related engagement of the hemispheres in visuospatial processing

Hemispheric asymmetries in visuospatial functions were investigated in women and men with a tachistoscopic task using lateralized presentation of "Necker" cubes. A lexical decision task served as control. In either of the two tasks the procedure involved a bilateral presentation of correct and distorted items and responses had to be given by means of a nonverbal decision task. The analysis of hits in the cube task showed a right visual field advantage for women and a left visual field advantage for men, but women had more false alarms in the right visual field, whereas men showed the reverse pattern again. The lexical decision task showed similar response patterns for men and women. The distinct response behavior supports the hypothesis that tasks allowing for various strategies to choose from obviously are better suited to elicit a differential engagement of the two hemispheres in women and men.

Effect of spatial ability and sex on EEG power in high school students

Performance at eight cognitive tests and EEG spectral power at rest was computed in 2 groups of men and women, between 17 and 21 years of age, with extreme degrees of spatial ability (SA) evaluated by the spatial relations subtest of the DAT: a low spatial ability group (10 men, 10 women) with scores below percentile 30 and a high spatial ability group (10 men, 10 women) with scores above percentile 80. Ten EEG artifact free samples, 4.096 sec each, were analyzed and absolute (AP) and relative power (RP) were obtained for 5 frequency bands using an FFT. EEG was submitted to principal component analysis and two way ANOVAs. High SA showed lower AP in the entire spectrum with eyes open and closed, and lower alpha 1 RP with eyes open than low SA group regardless of sex. The difference between low and high SA was better explained by high alpha AP at all derivations and high theta AP at right derivations and at left central and occipital regions. Women showed higher beta 1 and beta 2 AP at all derivations except at temporal regions than men regardless of SA scores.

EEG oscillations during menstrual cycle

12 sessions of EEG activity, one every second day, were recorded at F3, F4, C3, C4, P3, P4, O1 and O2 in 9 women with regular menstrual cycles. The following significant oscillations were observed: 1) absolute power was lower during periovulatory period; 2) absolute power of delta theta and alpha 1 was higher during premenstrual period whereas absolute power of alpha 2, beta 1 and beta 2 was higher during menstruation; 3) relative power of low alpha frequencies was lower and that of high frequencies was higher during premenstrual period; 4) interhemispheric correlation between frontals was higher during ovulation and between occipitals was higher during premenstrual phase; 5) no significant power asymmetries were observed. The present findings suggest higher activation of centro-parietal regions during menstruation and lower activation of frontal regions during premenstrual phase.

Task-induced differential cortical activation pattern

Measures of task-dependent cortical activation were assessed by bilateral EEG recordings from frontal, temporal, parietal and occipital areas. Two pictorial tests, the Raven Advanced Progressive Matrices and the Space Relations Test were used for verbal and spatial conditions, respectively. Recordings were obtained for 20 trials of each task from 22 right-handed adult males and 16 s. trial epochs were subjected to Fast Fourier analyses. Averaged intensity values for the alpha band were compared between verbal and spatial tasks for all subjects and between subgroups of verbalizers and visualizers, allotted on the basis of subject's performance index, derived from response speed and accuracy on the two tasks. The results were as follows: (1) The most pronounced EEG discriminators between the two performance subgroups are the left and right parietal and the right frontal area; (2) The left parietal zone provides the most pronounced discrimination between two groups; (3) There were significant interactions between the left parietal and the right frontal region; (4) The two parietal areas show characteristic frequency shifts in opposite directions for the task conditions. The findings imply complex interplay among the two parietal and right frontal areas, associated with sequential and holistic strategies. The results urge researchers to take into consideration subjectively preferred cognitive strategy, which along with objective task demands influences the process of problem solving and accompanying physiological changes.

Gender differences in the EEG during cognitive activity

EEG activity of 16 adult volunteers. 8 male and 8 females was monopolarly recorded at P3 and P4 at rest and during solution of three series of tasks: one analytic, one spatial and one mixed demanding both kinds of processing. The following main effects were observed: Men showed significantly higher beta relative power than women, while women showed significantly higher alpha relative power than men during all conditions. Alpha relative power decreased, while theta relative power increased during tasks solution in both sexes. Beta relative power was significantly higher at the left parietal only in men. Interparietal correlation was significantly higher in women than in men during all conditions and bands. For the theta band it increased from baseline values during tasks solution in men, while in women it decreased during the analytic task.

Testosterone, estradiol, ACTH and musical, spatial and verbal performance

Testosterone, estradiol, and ACTH were determined in blood serum of 26 healthy males aged 19.16 and of 25 healthy females aged 18.77 years on average, and results were correlated with test scores of three spatial tests, a verbal fluency measure, and a test measuring general musical ability. In addition, hemispheric lateralization for verbal material and handedness was assessed. While testosterone and estradiol alone were not significantly related to any of the cognitive or musical tests, testosterone/estradiol ratio was significantly negatively correlated with spatial tests, and ACTH was significantly positively correlated with spatial and musical tests. Correlations were stronger in females than in males. The laterality index was significantly negatively correlated with testosterone in males indicating that right hemisphere involvement in verbal processing was associated with high testosterone levels.

Enhanced right hemisphere activation in the mathematically precocious: a preliminary EEG investigation

A preliminary electroencephalographic (EEG) investigation was conducted to determine if the pattern of hemispheric activation in mathematically precocious youth differs from that of average math ability subjects. Alpha activity at four brain sites (frontal, temporal, parietal, and occipital lobes) over the left and right cerebral hemispheres (LH/RH) was monitored while 12- to 14-year-old, right-handed males: (a) looked at a blank slide (baseline condition), (b) judged which of two chimeric faces was "happier," and (c) determined if a word was a noun or a verb. At baseline, the LH of the precocious group was found to be more active at all four brain sites relative to that of the average ability group. During chimeric face processing, the gifted subjects exhibited a significant reduction in alpha power over the RH, primarily at the temporal lobe, while no such alpha suppression was observed in the average ability subjects. For noun/verb determinations, no significant alpha power reductions were obtained for either group. These electrophysiological data generally corroborate the behavioral findings of O'Boyle and Benbow (1990a) and support their contention that enhanced RH involvement during cognitive processing may be a correlate of mathematical precocity. Moreover, the pattern of activation observed across tasks suggests that the ability to effectively coordinate LH and RH processing resources at an early age may be linked to intellectual giftedness.

Sex differences in visual-spatial ability: the role of performance factors

Two studies were designed to explore the role of performance factors as sources of the frequently noted higher male scores on visual-spatial ability tests. In the first study, the mental rotations test (MRT) was administered to male and female college students of equally high quantitative ability (based on SAT math scores). Although males had significantly more correct responses on the test than did females, their advantage was eliminated when the ratio of correct responses to items attempted was used as the dependent measure. In the second study, the same test was administered to new groups of male and female college students. In this sample, the males had significantly higher SAT math scores. The MRT was administered under standard, timed conditions and under untimed conditions. Both raw and ratio scores were calculated. With SAT math score as the covariate, analyses of covariance indicated that males demonstrated higher performance in the timed, raw-score condition but not in the untimed or in the ratio-score conditions. The theoretical and social policy implications of these studies are discussed.

Correlation between EEG and cognitive abilities: sex differences

EEG activity was recorded during rest in 9 male and 9 female volunteers, aged 23 and 27, from C3, C4, T3, T4, P3, P4, O1 and O2, referenced to the ipsilateral earlobe. In a separate session verbal, spatial and abstract reasoning subtests of the Differential Aptitude Test were administered. Samples of EEG activity of 20.48 s were analysed and the interhemispheric correlation was obtained. Interhemispheric correlation in the alpha band was significantly higher in women than in men at central, parietal and occipital derivations. Significant correlations were found between D.A.T. scores and interhemispheric correlation, positive for women with abstract and spatial aptitudes in the central cortex, and negative for men with spatial, abstract and verbal scores in most derivations recorded. The opposite sign of men and women's correlations suggests the existence of a different cerebral functional organization, women showing lower hemispheric differentiation than men.

Sex differences in the lateralization of spatial abilities: a spatial component analysis of extreme group scores

Sex differences in the cerebral lateralization of two discrete components of spatial processing were investigated in high and low ability males and females using the dual-task paradigm. In the first phase of the experiment, the results indicated a pattern of right hemispheric control for a spatial visualization component, regardless of sex and ability level. In the processing of the spatial orientation component of spatial ability, high ability males and females showed left hemispheric lateralization, whereas low ability males and females displayed right hemispheric control. In the second phase of this study, it was observed that high ability females and low ability males may use a verbal mediation strategy in processing spatial visualization tasks. No verbal mediation effects were found for the spatial orientation component.