Sex differences in brain activity related to general and emotional intelligence

The study investigated gender differences in resting EEG (in three individually determined narrow alpha frequency bands) related to the level of general and emotional intelligence. Brain activity of males decreased with the level of general intelligence, whereas an opposite pattern of brain activity was observed in females. This difference was most pronounced in the upper-alpha band which is related to semantic memory processes. It was further found that highly intelligent males displayed greater decoupling of frontal brain areas, whereas highly intelligent females showed more coupling between frontal and parietal/occipital brain areas. Similar, but less significant differences were observed for the two area scores of strategic and experiential emotional intelligence. It appears that males and females have different resting EEG correlates of IQ.     

Sex differences in brain volume are related to specific skills, not to general intelligence

It has been proposed that males would show higher mean scores than females in general intelligence (g) because (1) men have, on average, larger brains than women, and (2) brain volume correlates with g. Here we report a failure to support the conclusion derived from these premises. High resolution MRIs were acquired in a sample of one hundred healthy young participants for estimating total, gray, and white matter volumes. Participants also completed an intelligence battery - comprising tests measuring abstract, verbal, and spatial abilities - that allowed the extraction of g scores. Results showed consistent relations between sex differences in brain volumes and non-g spatial and verbal skills but not for g.     

Sex differences in personality are larger in gender equal countries: Replicating and extending a surprising finding

Sex differences in personality have been shown to be larger in more gender equal countries. We advance this research by using an extensive personality measure, the IPIP‐NEO‐120, with large country samples (N > 1000), from 22 countries. Furthermore, to capture the multidimensionality of personality we measure sex differences with a multivariate effect size (Mahalanobis distance D). Results indicate that past research, using univariate measures of effect size, have underestimated the size of between‐country sex differences in personality. Confirming past research, there was a strong correlation (r = .69) between a country's sex differences in personality and their Gender Equality Index. Additional analyses showed that women typically score higher than men on all five trait factors (Neuroticism, Extraversion, Openness, Agreeableness and Conscientiousness), and that these relative differences are larger in more gender equal countries. We speculate that as gender equality increases both men and women gravitate towards their traditional gender roles.     

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.     

Sex differences in the IQ-white matter microstructure relationship: A DTI study

Sex differences in the relationship between general intelligence and brain structure are a topic of increasing research interest. Early studies focused mainly on gray and white matter differences using voxel-based morphometry, while more recent studies investigated neural fiber tracts using diffusion tensor imaging (DTI) to analyze the white matter microstructure. In this study we used tract-based spatial statistics (TBSS) on DTI to test how intelligence is associated with brain diffusion indices and to see whether this relationship differs between men and women. 63 Men and women divided into groups of lower and higher intelligence were selected. Whole-brain DTI scans were analyzed using TBSS calculating maps of fractional anisotropy (FA), radial diffusivity (RD), and axial diffusivity (AD). The results reveal that the white matter microstructure differs between individuals as a function of intelligence and sex. In men, higher intelligence was related to higher FA and lower RD in the corpus callosum. In women, in contrast, intelligence was not related to the white matter microstructure. The higher values of FA and lower values of RD suggest that intelligence is associated with higher myelination and/or a higher number of axons particularly in men. This microstructural difference in the corpus callosum may increase cognitive functioning by reducing inter-hemispheric transfer time and thus account for more efficient brain functioning in men.     

A longitudinal study of sex differences in intelligence at ages 7, 11 and 16 years

This paper presents the results of a longitudinal study of sex differences in intelligence as a test of Lynn’s (1994) hypothesis that from the age of 16 years males develop higher average intelligence than females. The results show that at the ages of 7 and 11 years girls have an IQ advantage of approximately 1 IQ point, but at the age of 16 years this changes in the same boys and girls to an IQ advantage of 1.8 IQ points for boys.     

Cross-sectional age differences in the HEXACO personality: Results from a Japanese sample

Little research has been conducted on personality development in non-Western countries. The present study investigated age differences in personality in Japanese middle adults (N = 2000; M = 40.94 years; SD = 5.35, range 30–49; 1000 women). After controlling for educational level, annual income, marital status, and gender, it was found that the level of Emotionality was negatively associated with age. Honesty–Humility, on the other hand, was positively associated with age. However, Extraversion, Agreeableness, Conscientiousness, and Openness were not associated with the participant age. These findings suggest that trends in personality development may differ slightly between Western and non-Western countries.     

How personality relates to intelligence test performance: Implications for a theory of intelligence,ageing research and personality assessment

Previously reported findings indicate that variation of EEG evoked potential parameters is strongly related to both personality and intelligence differences (Robinson, 1982a, b). These data and the associated theory imply that personality should relate to intelligence test performance. Results are described in this report which indicate that subtest profiles obtained with the Wechsler Adult Intelligence Scale (WAIS) differ significantly for Ss scoring highest and lowest on the Extraversion (E) scale of the Eysenck Personality Questionnaire (EPQ); introverts tend to do better on the ‘Verbal’ subtests while extraverts tend to do better on the ‘Performance’ measures. Ss with middling scores on the E scale of the EPQ can also be distinguished in terms of specific WAIS profiles. In this case the results define two contrasting groups. Young male Ss with middling E scores tend to have high Psychoticism (P) and low Lie (L) scores on the EPQ as well as having distinctive WAIS profiles characterized by higher scores on subtests normally associated with a ‘Memory’ or ‘Attention-Concentration’ factor. Higher scores were also obtained by this subgroup on the Picture Arrangement and Block Design subtests which were previously shown to load a P + /L ? factor. The converse is true for older female Ss who also have middling E scores. As well as demonstrating a systematic relationship between personality and intelligence test performance these data provide some further support for a model of brain-behaviour relationships proposed by Robinson. Within this theoretical framework a neurophysiologically meaningful explanation can be provided for the three major factors that reliably emerge in factor-analytic studies of the WAIS. From an applied viewpoint, the data indicate that personality differences can be assessed from performance on tests such as the WAIS. On this issue the results are discussed with particular reference to Gittinger's Personality Assessment System. Implications for ageing research are also discussed.     

Cross-sectional age differences in personality: Evidence from nationally representative samples from Switzerland and the United States

Identifying reliable patterns of age differences in personality can help clarify the nature of adult personality development. Previous studies have been limited because many have relied on convenience samples. In this study, we examined age differences in personality in two nationally representative samples, one from Switzerland and one from the United States. The results indicated that Agreeableness and Conscientiousness were positively associated with age, whereas Extraversion was negatively associated with age. However, the magnitude of age differences for Extraversion was much smaller than for Agreeableness and Conscientiousness. Openness showed a more complex trend such that 30- to 34-year-olds scored lower on Openness than younger age groups, whereas older groups scored somewhere in between. Inconsistent age differences were observed for Neuroticism.     

Sources of variability in working memory in early childhood: A consideration of age, temperament, language, and brain electrical activity

This study investigated age-related differences in working memory and inhibitory control (WMIC) in -, 4-, and -year-olds and how these differences were associated with differences in regulatory aspects of temperament, language comprehension, and brain electrical activity. A series of cognitive control tasks was administered to measure WMIC ability, including the Stroop-like day–night and the yes–no tasks. Baseline and task electroencephalographic data were collected. The Children's Behavior Questionnaire was used to assess caregiver perceptions of temperament with a particular interest in the effortful control and surgency factors, and language comprehension was measured with the Peabody-Picture Vocabulary Test-III. The results of this study demonstrated differential temperament-cognition relations for the three age groups, as positive associations were found between WMIC and effortful control for the - and 4-year-olds and negative associations were found between WMIC and surgency for the -year-olds. An increasingly robust relation between WMIC and language comprehension was demonstrated across the three age groups, as well as differential patterns of task-related brain electrical activity.     

Relations between nonverbal intelligence and personality reports in late childhood

We investigated relations between children’s personality and their nonverbal intelligence.Simple correlations showed that children’s intelligence was positively associated with self-reported benevolence levels and with parental reports on their conscientiousness and imagination levels. Regression analyses revealed a more complex association pattern, with intelligence/personality correlations being moderated by the variables of child and parent gender. Results also yielded a lower personality domain overlap for children with higher IQ, in agreement with the differentiation hypothesis.     

Proneness for psychological flow in everyday life: Associations with personality and intelligence

Flow is an experience of enjoyment, concentration, and low self-awareness that occurs during active task performance. We investigated associations between the tendency to experience flow (flow proneness), Big Five personality traits and intelligence in two samples. We hypothesized a negative relation between flow proneness and neuroticism, since negative affect could interfere with the affective component of flow. Secondly, since sustained attention is a component of flow, we tested whether flow proneness is positively related to intelligence. Sample 1 included 137 individuals who completed tests for flow proneness, intelligence, and Big Five personality. In Sample 2 (all twins; n = 2539), flow proneness and intelligence, but not personality, were measured. As hypothesized, we found a negative correlation between flow proneness and neuroticism in Sample 1. Additional exploratory analyses revealed a positive association between flow proneness and conscientiousness. There was no correlation between flow proneness and intelligence. Although significant for some comparisons, associations between intelligence and flow proneness were also very weak in Sample 2. We conclude that flow proneness is associated with personality rather than intelligence, and discuss that flow may be a state of effortless attention that relies on different mechanisms from those involved in attention during mental effort.     

The associations of birth order with personality and intelligence in a representative sample of U.S. high school students

We tested birth order associations with personality traits and intelligence using Project Talent, a representative sample (N = 377,000) of U.S. high school students. Using a between-family design and several background factors (i.e., age, sex, sibship size, parental socio-economic status, and family structure), we were able to control for potential confounds, and estimate the links between birth order and outcomes across several different social categories. In addition to differences between firstborns and laterborns across the entire sample, we also tested birth rank trends in a sub-sample of targets from sibships of three, raised by two parents. Overall, the average absolute association between birth order and personality traits was .02, whereas the one between birth order and intelligence was .04.     

How brain arousal systems determine different temperament types and the major dimensions of personality

Theory and research is described which led to the hypothesis that the choleric (E+N+) and melancholic (E−N+) temperaments are determined by differences in thalamocortical inhibition of brain-stem processes. An opportunity to test this hypothesis was provided by the recent discovery of 4, 7, and 10 Hz response waves confounded in EEG averaged evoked potentials [Robinson, D. L. (1999b). The technical, neurological, and psychological significance of ‘alpha’ ‘theta’ and ‘delta’ waves confounded in EEG evoked potentials: 1. A study of peak latencies. Electroencephalography and Clinical Neurophysiology, 110, 1427–1434; (2000). The technical neurological, and psychological significance of ‘alpha’, ‘delta’, and ‘theta’ waves confounded in EEG evoked potentials: A study of peak amplitudes. Personality and Individual Differences, 28, 673–693]. These responses are attributed to the brain-stem, limbic, and thalamocortical arousal systems, respectively, and in the cited reports principal components analysis of data obtained from 93 participants confirmed the existence of predicted excitatory and inhibitory relationships. ANOVA was used in the present study to test the further prediction that there should be strong inhibition of the 4 Hz system by the 10 Hz system in melancholics (E−N+) and weak inhibition of the 4 Hz system in cholerics (E+N+), with median inhibition predicted for the other temperament types. There was a large and statistically significant difference between the mean scores on the PCA inhibition factor obtained for the temperament groups, with temperament defined in terms of high and low EPQ extraversion (E) and neuroticism (N) scores. The significance of these results is discussed with reference to fundamental questions raised by Pavlov's pioneering research but left unanswered for the best part of a century. Implications for the future conduct of personality research are also considered.     

Relationships between factors of intelligence and brain volume

The recent explosion of studies aimed at determining the biological basis of intelligence has revealed that cognitive ability has a strong biological substrate. This study expands on this literature by examining the relation between cognitive ability and MRI-measured brain volume and head size in a sample of adult male siblings recruited from the London, Ontario community in Canada. It was found that brain volume correlated with IQ at 0.35 (P<0.01), thus replicating the results of past studies. Corrections for restriction of range and attenuation in both this and past studies suggest that the population value of the brain volume-IQ correlation is closer to 0.50. Head size variables, with one exception, also showed the expected positive correlations with IQ. The results of a vector analysis on factor scores indicated that the more highly g-loaded a test was the more highly it correlated with brain volume (r=0.59, P<0.01). The sum of the data suggested that although brain volume (and to a lesser extent, head size) is predictive of g, fluid ability, and memory, it does not predict crystallized ability. Unexpectedly, the higher the spatial imaging loading of a test, the less its correlation with brain volume (vector correlation=−0.84, P<0.001).     

Cerebral lateralization and general intelligence: gender differences in a transcranial Doppler study

The present study evaluated cerebral lateralization during Raven's progressive matrices (RPM) paradigm in female and male subjects. Bilateral simultaneous transcranial Doppler (TCD) ultrasound was used to measure mean blood flow velocities (MBFV) in the right and left middle cerebral arteries (MCAs) in 24 (15 females and 9 males) right-handed normal subjects. The female subjects used a left hemisphere strategy, while males used a right hemisphere strategy to successfully solve RPM tasks. This implies that general intelligence is associated with neural systems within one hemisphere that are accessible to a variety of cognitive processes.     

Sex differences in the Schizotypal Personality Questionnaire Brief among Japanese employees and undergraduates: A cross-sectional study

Schizotypal personality may be seen as an indicator predisposition to schizophrenia and psychosis proneness. Schizotypal personality traits behave differently depending on a person’s age and sex, but few studies have examined the causal relationship between age-related sex differences and schizotypal personality traits. The aim of the present study was to examine the relationship between the schizotypal personality and sex in different age groups. In our study, we used the Schizotypal Personality Questionnaire Brief (SPQ-B). Participants were 371 college students (107 men) with an age range from 18 to 25 years, and 322 working people (156 men) with an age range of 22–67 years. The results showed that the young adult males in the college student group had tendencies to score higher than females in the same group on the SPQ-B total score and its two subscale scores (the cognitive-perceptual and the interpersonal scores). In the adult sample taken in the working people group, the total score and subscale scores of the SPQ-B did not significantly discriminate male subjects from female subjects. These findings indicate that sex differences of schizotypal personality traits may reflect differential age-related variation.     

In search of the arousal procrastinator: Investigating the relation between procrastination, arousal-based personality traits and beliefs about procrastination motivations

Arousal procrastination was investigated to determine: (a) If the General Procrastination Scale (GP; Lay, 1986) measures procrastination motivated by arousal, and (b) whether sensation seeking (SS), extraversion (E), and the reducer index (R) account for variance in beliefs about the motivation for academic procrastination. Participants were 311 undergraduate students (60.1% female), primarily Caucasian (63.3%), with a mean age of 20.09 (SD = 3.08). An online questionnaire package included measures of procrastination and 3 arousal-based personality inventories. A factor analysis of the GP and the Sensation Seeking Scale-V (SSS-V; Zuckerman, Eysenck, & Eysenck, 1978) produced six factors with the GP and SSS-V items loading on separate factors, indicating no relation. A regression analysis revealed that SS, E, and R together accounted for 5.2% of the variance in participants’ arousal-related beliefs motivating their procrastination. These results challenge the existing literature claiming that the GP is a measure of arousal procrastination, but do indicate that some individuals believe that their procrastination is motivated by a need for heightened arousal.     

Confirmation of correlation between brain nerve conduction velocity and intelligence level in normal adults

In 1992, Reed and Jensen [Intelligence 16 (1992) 259–272] reported a positive correlation (.26; p=.002; .37 after correcting for restricted intelligence range) between a brain nerve conduction velocity (NCV) and intelligence level in 147 normal male students. In the first follow-up of their study, we report on a study using similar NCV methodologies, but testing both male and female students and using more extensive measures of cognitive abilities. One-hundred eighty-six males and 201 females, aged 18–25 years, were tested in three different NCV conditions and with nine cognitive tests, including Raven Progressive Matrices as used by Reed and Jensen. None of the 27 independent correlations in either the males or in the females are significant at Bonferroni-corrected probability levels, but 25 of 27 correlations in males and 20 of 27 correlations in females have positive signs. The exact binomial probabilities for these results are 5.6×10⁻⁶ and .002, respectively. We discuss possible reasons for the differences between the results of Reed and Jensen and our results. We also find that males have four percent faster NCVs than females with each of the three test conditions, probably due to their faster increase of white matter in the brain during adolescence.     

At the interface of social cognition and psychometrics: Manipulating the sex of the reference class modulates sex differences in personality traits

Psychometric surveys suggest that sex differences in personality are minimal. Herein, we argue that (a) the mind is likely biased toward assessing oneself relative to same-sex others, and (b) this bias may affect the measurement of sex differences in personality. In support of this, an experiment demonstrates modulation of sex differences on the HEXACO facets by manipulating the sex of the “reference class”—the group of people subjects compare themselves to when making self-assessments on survey items. Although patterns varied across traits, sex differences were relatively small in the “unspecified” and “same-sex” reference class conditions—but substantially larger in the “opposite-sex” condition. These findings point to a same-sex comparison bias that may impact the measurement of sex differences in personality.