Gray matter and intelligence factors: Is there a neuro-g?

Heterogeneous results among neuro-imaging studies using psychometric intelligence measures may result from the variety of tests used. The g-factor may provide a common metric across studies. Here we derived a g-factor from a battery of eight cognitive tests completed by 6929 young adults, 40 of whom also completed structural MRI scans. Regional gray matter (GM) was determined using voxel-based-morphometry (VBM) and correlated to g-scores. Results showed correlations distributed throughout the brain, but there was limited overlap with brain areas identified in a similar study that used a different battery of tests to derive g-scores. Comparable spatial scores (with g variance removed) also were derived from both batteries, and there was considerable overlap in brain areas where GM was correlated to the respective spatial scores. The results indicate that g-scores derived from different test batteries do not necessarily have equivalent neuro-anatomical substrates, suggesting that identifying a “neuro-g” will be difficult. The neuro-anatomical substrate of a spatial factor, however, appears more consistent and implicates a distributed network of brain areas that may be involved with spatial ability. Future imaging studies directed at identifying the neural basis of intelligence may benefit from using a psychometric test battery chosen with specific criteria.     

Hippocampal structure and human cognition: Key role of spatial processing and evidence supporting the efficiency hypothesis in females

Here we apply a method for automated segmentation of the hippocampus in 3D high-resolution structural brain MRI scans. One hundred and four healthy young adults completed twenty one tasks measuring abstract, verbal, and spatial intelligence, along with working memory, executive control, attention, and processing speed. After permutation tests corrected for multiple comparisons across vertices (p < .05), significant relationships were found for spatial intelligence, spatial working memory, and spatial executive control. Interactions with sex revealed significant relationships with the general factor of intelligence (g), along with abstract and spatial intelligence. These correlations were mainly positive for males but negative for females, which might support the efficiency hypothesis in women. Verbal intelligence, attention, and processing speed were not related to hippocampal structural differences.     

Associations between cortical thickness and general intelligence in children,adolescents and young adults

Neuroimaging research indicates that human intellectual ability is related to brain structure including the thickness of the cerebral cortex. Most studies indicate that general intelligence is positively associated with cortical thickness in areas of association cortex distributed throughout both brain hemispheres. In this study, we performed a cortical thickness mapping analysis on data from 182 healthy typically developing males and females ages 9 to 24 years to identify correlates of general intelligence (g) scores. To determine if these correlates also mediate associations of specific cognitive abilities with cortical thickness, we regressed specific cognitive test scores on g scores and analyzed the residuals with respect to cortical thickness. The effect of age on the association between cortical thickness and intelligence was examined. We found a widely distributed pattern of positive associations between cortical thickness and g scores, as derived from the first unrotated principal factor of a factor analysis of Wechsler Abbreviated Scale of Intelligence (WASI) subtest scores. After WASI specific cognitive subtest scores were regressed on g factor scores, the residual score variances did not correlate significantly with cortical thickness in the full sample with age covaried. When participants were grouped at the age median, significant positive associations of cortical thickness were obtained in the older group for g-residualized scores on Block Design (a measure of visual-motor integrative processing) while significant negative associations of cortical thickness were observed in the younger group for g-residualized Vocabulary scores. These results regarding correlates of general intelligence are concordant with the existing literature, while the findings from younger versus older subgroups have implications for future research on brain structural correlates of specific cognitive abilities, as well as the cognitive domain specificity of behavioral performance correlates of normative gray matter thinning during adolescence.     

Finding the g-factor in brain structure using the method of correlated vectors

It is unclear whether brain mechanisms underlying human intelligence are distributed throughout the brain or mainly concentrated in the frontal lobes. Data are inconsistent possibly due, at least in part, to the different ways the construct of intelligence is measured. Here we apply the method of correlated vectors to determine how the general factor of intelligence (g) is related to regional gray matter and white matter volumes. This is a re-analysis of an earlier study showing regional gray matter and white matter volume is correlated to Full Scale IQ (FSIQ). However, it is well-known that FSIQ taps several cognitive abilities and skills in addition to g. The results now show that the g factor accounts for several but not all FSIQ/gray matter correlations distributed throughout the brain and these areas may differ for young and older adults.     

Gray matter correlates of fluid,crystallized, and spatial intelligence: Testing the P-FIT model

The parieto-frontal integration theory (P-FIT) nominates several areas distributed throughout the brain as relevant for intelligence. This theory was derived from previously published studies using a variety of both imaging methods and tests of cognitive ability. Here we test this theory in a new sample of young healthy adults (N = 100) using a psychometric battery tapping fluid, crystallized, and spatial intelligence factors. High resolution structural MRI scans (3T) were obtained and analyzed with Voxel-based Morphometry (VBM). The main findings are consistent with the P-FIT, supporting the view that general intelligence (g) involves multiple cortical areas throughout the brain. Key regions include the dorsolateral prefrontal cortex, Broca's and Wernicke's areas, the somato-sensory association cortex, and the visual association cortex. Further, estimates of crystallized and spatial intelligence with g statistically removed, still share several brain areas with general intelligence, but also show some degree of uniqueness.     

The structure of working memory and how it relates to intelligence in children

This study explored the structure of working memory, and its relationship with intelligence in 176 typically-developing children in the 4th and 5th grades at school. Different measures of working memory (WM), and intelligence (g) were administered. Confirmatory factor analyses showed that WM involves an attentional control system and storage aspects that rely on domain-specific verbal (STM-V) and visuospatial (STM-VS) resources. The structural equation models showed that WM predicts a large portion (66%) of the variance in g, confirming that the two constructs are separable but closely related in young children. Findings also showed that only WM and STM-VS are significantly related to g, while the contribution of STM-V is moderate. Theoretical implications for the relationship between WM and g are discussed.     

Memory span and general intelligence: A latent-variable approach

There are several studies showing that working memory and intelligence are strongly related. However, working memory tasks require simultaneous processing and storage, so the causes of their relationship with intelligence are currently a matter of discussion. The present study examined the simultaneous relationships among short-term memory (STM), working memory (WM), and general intelligence (g). Two hundred and eight participants performed six verbal, quantitative, and spatial STM tasks, six verbal, quantitative, and spatial WM tasks, and eight tests measuring fluid, crystallized, spatial, and quantitative intelligence. Especial care is taken to avoid misrepresenting the relations among the constructs being studied because of specific task variance. Structural equation modelling (SEM) results revealed that (a) WM and g are (almost) isomorphic constructs, (b) the isomorphism vanishes when the storage component of WM is partialed out, and (c) STM and WM (with its storage component partialed out) predict g.     

Is g an entity? A Japanese twin study using syllogisms and intelligence tests

Using a behavioral genetic approach, we examined the validity of the hypothesis concerning the singularity of human general intelligence, the g theory, by analyzing data from two tests: the first consisted of 100 syllogism problems and the second a full-scale intelligence test. The participants were 448 Japanese young adult twins (167 pairs of identical and 53 pairs of fraternal twins). Data were analyzed for their fit to two kinds of multivariate genetic models: a common pathway model, in which a higher-order latent variable, g, was postulated as an entity; and an independent pathway model, in which the higher-order latent variable was not posited. These analyses revealed that the common pathway model which included additive genetic and nonshared environmental factors best accounted for the three distinct mental abilities: syllogistic logical deductive reasoning, verbal, and spatial. Both the substantial g-loading for syllogism-solving, historically recognized as the symbol of human intelligence, and the emergence of g as an entity at an etiological level, that is, at the genetic and environmental factor level, provide further support for the g theory.     

The Relationship Between Diverse Components of Intelligence and Creativity

Intelligence and creativity are accounted for in terms of two different mental operations referred to as ‘convergent thinking’ and ‘divergent thinking’, respectively. Nevertheless, psychometric evidence on the relationship between intelligence and creativity has been controversial. To clarify their relationship, we characterized the relationship between diverse components of intelligence and creativity through the administration of psychometric tests on a large sample (WAIS, RPM, and TTCT‐figural: n = 215; TTCT‐verbal: n = 137). The general intelligence factor (g) score showed significant correlations with both TTCT‐figural and TTCT‐verbal scores. However, sub‐dimensional analysis demonstrated that their association was attributable to the specific components of both TTCTs (TTCT‐figural: Abstractness of Titles, Elaboration, and Resistance to Premature Closure; TTCT‐verbal: Flexibility) rather than to their common components (Fluency and Originality). Among the intelligence sub‐dimensions, crystallized intelligence (gC) played a pivotal role in the association between g and the specific components of both TTCTs. When the total sample was divided into two IQ groups, these phenomena were more evident in the average IQ group than in the high IQ group. These results suggest that the mental operation of creativity may be different from that of intelligence, but gC may be used as a resource for the mental operation of creativity.     

Relations between mental performance and reaction time: New aspects of an old problem

The relation between simple and complex reaction time and psychometrically determined mental performance was reexamined with 486 subjects of above-average intelligence. Various standardized tests measuring aspects of cognitive ability, memory and ability to concentrate were used. Simple and complex reaction times were measured using the Klebelsberg modification of the Mierke apparatus. Correlations between complex reaction time and mental performance as observed by other investigators were mostly confirmed. We found, however, the strongest and most consistent correlations with tests measuring short-term memory; ability to concentrate and spatial ability. On the other hand, tests known and shown again in this paper to load highly on Spearman's general factor g, such as verbal abilities; combinatoric thinking; abstraction; or calculation gave only trivial, and, in most cases, nonsignificant correlations with complex reaction time. We even observed a negative (though, for our data, not significant) correlation between g-loadings of subtests and their correlations with complex reaction time for the only complete standardized intelligence test used in this study, the “Intelligenz-Strukturtest (Amthauer).” Therefore, this study does not support the hypothesis that fast processing of complex information as measured by complex reaction time is the decisive component of the general factor of intelligence g.     

A smarter brain is associated with stronger neural interaction in healthy young females: A resting EEG coherence study

General intelligence, the g factor, is a major issue in psychology and neuroscience. However, the neural mechanism of the g factor is still not clear. It is suggested that the g factor should be non-modular (a property across the brain) and show good colinearity with various cognitive tests. This study examines the hypothesis that functional connectivity may be a good candidate for the g factor. We recorded resting state eyes-closed EEG signals in 184 healthy young females. Coherence values of 38 selected channel pairs across delta, theta, alpha, beta and gamma frequencies were correlated with six intelligence quotient (IQ) subtests, including symbol search, block design, object assembly, digit span, similarity and arithmetic. A three-stage analytic flow was constructed to delineate common (g factor) and unique neural components of intelligence. It is noticed that the coherence pattern demonstrates good correlation with five of the IQ subtests (except symbol search) and non-modularity in the brain. Our commonality analyses support connectivity strength in the brain as a good indicator of the g factor. For the digit span and arithmetic tests, the uniqueness analyses provide left-lateralized topography relevant to the operation of working memory. Performance on the arithmetic test is further correlated with strengths at left temporo-parietal and bilateral temporal connections. All the significant correlations are positive, indicating that the stronger the connectivity strengths, the higher the intelligence. Our analyses conclude that a smarter brain is associated with stronger interaction in the central nervous system. The implication and why the symbol search does not show parallel results are discussed.     

Cognitive reserve as a moderator of responsiveness to an online problem-solving intervention for adolescents with complicated mild-to-severe traumatic brain injury

Children and adolescents with traumatic brain injury (TBI) often experience behavior difficulties that may arise from problem-solving deficits and impaired self-regulation. However, little is known about the relationship of neurocognitive ability to post-TBI behavioral recovery. To address this question, we examined whether verbal intelligence, as estimated by Vocabulary scores from the Wechsler Abbreviated Scale of Intelligence, predicted improvements in behavior and executive functioning following a problem-solving intervention for adolescents with TBI. One hundred and thirty-two adolescents with complicated mild-to-severe TBI were randomly assigned to a six-month Web-based problem-solving intervention (CAPS; n = 65) or to an Internet resource comparison (IRC; n = 67) group. Vocabulary moderated the association between treatment group and improvements in metacognitive abilities. Examination of the mean estimates indicated that for those with lower Vocabulary scores, pre-intervention Metacognition Index scores from the Behavior Rating Inventory of Executive Function (BRIEF) did not differ between the groups, but post-intervention scores were significantly lower (more improved) for those in the CAPS group. These findings suggest that low verbal intelligence was associated with greater improvements in executive functioning following the CAPS intervention and that verbal intelligence may have an important role in response to intervention for TBI. Understanding predictors of responsiveness to interventions allows clinicians to tailor treatments to individuals, thus improving efficacy.     

Parents Think Their Sons Are Brighter Than Their Daughters: Sex Differences in Parental Self-Estimations and Estimations of Their Children's Multiple Intelligences

In this study, 156 participants, predominantly White British adults (M age = 44.3 years) rated themselves on overall IQ and on H. Gardner's (1983) 7 intelligence subtypes. Parents (n = 120) also estimated the intelligence of their children. Men's self-estimates were significantly higher than women's (110.15 vs. 104.84). Participants thought their verbal, mathematical, and spatial intelligence scores were the best indicators of their own overall intelligence. Parents estimated that their sons had significantly higher IQs than their daughters (115.21 vs. 107.49). Self-estimates and estimates of children's multiple intelligences were higher for men and sons, significantly so for logical-mathematical and spatial intelligence. Parents rated 2nd-born daughters as having significantly higher verbal and musical intelligence than their male counterparts. Higher parental IQ self-estimates corresponded with higher IQ estimates for children. Results for 1st-born children were clearest and showed the most significant differences. The findings are interpreted in terms of sociocultural and familial influences and the possibility of actual sex differences in particular abilities.     

Clocking g: Relating intelligence and measures of timed performance

The relationships between intelligence test scores and measures derived from reaction time (RT) and perceptual speed procedures were investigated in 137 twelve-year-old students with IQs ranging from 59 to 142. A range of intelligence tests were used and the scores factor analyzed to produce general, spatial and verbal factors. Test and factor scores were correlated with perceptual speed and with measures taken from 2, 4, and 8 choice RT tasks using a response keyboard upon which the subject's fingers directly rested, thus avoiding interpretive problems associated with a “home key.” Inspection time correlated poorly with intelligence. Only three of the RT measures produced correlations greater than .25 with the general factor. These were the slope of Hick's law, B, (correlation −.28), the 8 choice mean RT, RT8, (−.33) and the 8 choice standard deviation, SD8 (−.41), compared with the average intercorrelation between the intelligence measures of .40. Test-retest correlations of the RT measures, taken over a year for half the subjects, were low as reliability measures, with .35 for B, .52 for RT8, and .48 for SD8. Correlations of RT measures with spatial scores were not significantly greater than with verbal scores, suggesting that whatever relationship exists is with a general factor rather than only a spatial one.     

Do sex differences in a faceted model of fluid and crystallized intelligence depend on the method applied?

Recently, different methodological approaches have been discussed as an explanation for inconsistencies in studies investigating sex differences in different intelligences. The present study investigates sex differences in manifest sum scores, factor score estimates, and latent verbal, numerical, figural intelligence, as well as fluid and crystallized intelligence as measured by the German Intelligence-Structure-Test 2000-R (IST 2000-R; Liepmann, Beauducel, Brocke, & Amthauer, 2007). The not population-representative sample consisted of 977 German 11th and 12th graders enrolled in a “Gymnasium” (551 female; mean age: M = 16.70; SD = 0.65) who completed the IST 2000-R. Sex differences in fluid and crystallized intelligence were not influenced by the method applied with men performing better than women. However, extent and direction of sex differences in verbal, numerical, and figural intelligence differed by the method applied. Whereas there was a male advantage in all three factors measured as manifest sum scores, women performed better in verbal intelligence as measured by factor scores or as latent variables. Effect sizes of sex differences in numerical and figural intelligence were also greatly reduced when applying the latter two methods. Results are discussed with regard to their theoretical and practical implications.     

Cognitive ability, right-wing authoritarianism, and social dominance orientation: A five-year longitudinal study amongst adolescents

We report longitudinal data in which we assessed the relationships between intelligence and support for two constructs that shape ideological frameworks, namely, right-wing authoritarianism (RWA) and social dominance orientation (SDO). Participants (N = 375) were assessed in Grade 7 and again in Grade 12. Verbal and numerical ability were assessed when students entered high school in Grade 7. RWA and SDO were assessed before school graduation in Grade 12. After controlling for the possible confounding effects of personality and religious values in Grade 12, RWA was predicted by low g (β = − .16) and low verbal intelligence (β = − .18). SDO was predicted by low verbal intelligence only (β = − .13). These results are discussed with reference to the role of verbal intelligence in predicting support for such ideological frameworks and some comments are offered regarding the cognitive distinctions between RWA and SDO.     

On the interpretation of the CHC factor Gc

On the one hand, the factors Gf and Gc in the Cattell-Horn-Carroll (CHC) model of intelligence are hypothesized to represent individual differences in unique psychological or biological capacities. On the other hand, they are interpreted as representing the theoretical variables fluid and crystallized intelligence in investment theory. With respect to Gc, this leads to a theoretical conflict because in investment theory crystallized intelligence is not a capacity but purely a statistical entity. We contend that if CHC factor Gc represents a capacity, it cannot represent crystallized intelligence, and if Gc represents crystallized intelligence, it does not represent a capacity. In addition, from our discussion of Gc, we conclude that in investment theory the factors Gf and g represent one and the same capacity. In support of our theoretical conclusions, we implemented the CHC model in a confirmatory factor analysis of a HCA (Human Cognitive Abilities project) data set. As expected, Gf and g were statistically indistinguishable. Gc was effectively absent, because it was statistically equivalent to verbal comprehension. Factors Gc and g could be removed from the model without any reduction in model fit. We argue that in the CHC taxonomy the factors Gc and g are redundant as explanatory variables.     

Critical flicker frequency and intelligence

Tests of verbal intelligence (Concept Mastery Test) and nonverbal intelligence (Raven's Advanced Progressive Matrices) showed nonsignificant zero-order correlations and a nonsignificant multiple correlation with critical flicker frequency (CFF), in 100 university students. Age-partialled correlations were even lower, and corrections for attenuation and restriction of range yielded unimpressive results. It was concluded that CFF has a negligible relationship to psychometric intelligence and is probably a poor tool in the investigation of the nature of g.     

Brain mechanisms and intelligence. Psychometric g and executive function

Sternberg [Sternberg, R.J. (1985). Beyond IQ: a triarchic theory of human intelligence. New York: Cambridge Univ. Press.] has proposed that the general intelligence, or the g factor, obtained when batteries of mental tests are factor analyzed, is a reflection of the fact that executive functions (EF) are common to all cognitive tests. Three lines of evidence that fail to support Sternberg's formulation are presented. First, in animal problem solving studies, there is only a modest degree of overlap between brain structures that are critical for g, and brain structures that have been identified as the rodent EF system. Second, children with attention deficit-hyperactivity disorder (ADHD), characterized by EF dysfunction, do not have IQ scores that are lower, on average, than children in the test standardization populations. Third, human frontal lobe patients often have clear EF deficits, but IQ (a next-best estimate of g) may be preserved. These findings cast serious doubt on the plausibility of Sternberg's formulation. Clarifying the distinction between psychometric g and EF can be important for understanding the differences between practical and psychometric intelligence.     

Exposure to severe urban air pollution influences cognitive outcomes, brain volume and systemic inflammation in clinically healthy children

Exposure to severe air pollution produces neuroinflammation and structural brain alterations in children. We tested whether patterns of brain growth, cognitive deficits and white matter hyperintensities (WMH) are associated with exposures to severe air pollution. Baseline and 1 year follow-up measurements of global and regional brain MRI volumes, cognitive abilities (Wechsler Intelligence Scale for Children-Revised, WISC-R), and serum inflammatory mediators were collected in 20 Mexico City (MC) children (10 with white matter hyperintensities, WMH⁺, and 10 without, WMH⁻) and 10 matched controls (CTL) from a low polluted city. There were significant differences in white matter volumes between CTL and MC children - both WMH⁺ and WMH⁻ - in right parietal and bilateral temporal areas. Both WMH⁻ and WMH⁺ MC children showed progressive deficits, compared to CTL children, on the WISC-R Vocabulary and Digit Span subtests. The cognitive deficits in highly exposed children match the localization of the volumetric differences detected over the 1 year follow-up, since the deficits observed are consistent with impairment of parietal and temporal lobe functions. Regardless of the presence of prefrontal WMH, Mexico City children performed more poorly across a variety of cognitive tests, compared to CTL children, thus WMH⁺ is likely only partially identifying underlying white matter pathology. Together these findings reveal that exposure to air pollution may perturb the trajectory of cerebral development and result in cognitive deficits during childhood.