Intelligence and neural efficiency: Measures of brain activation versus measures of functional connectivity in the brain

The neural efficiency hypothesis of intelligence suggests a more efficient use of the cortex (or even the brain) in brighter as compared to less intelligent individuals. This has been shown in a series of studies employing different neurophysiological measurement methods and a broad range of different cognitive task demands. However, most of the studies dealing with the brain–IQ relationship used parameters of absolute or relative brain activation such as the event-related (de-)synchronization of EEG alpha activity, allowing for interpretations in terms of more or less brain activation when individuals are confronted with cognitively demanding tasks. In order to investigate the neural efficiency hypothesis more thoroughly, we also used measures that inform us about functional connectivity between different brain areas (or functional coupling, respectively) when engaged in cognitive task performance. Analyses reveal evidence that higher intelligence is associated with a lower brain activation (or a lower ERD, respectively) and a stronger phase locking between short-distant regions of the frontal cortex.     

A male advantage for spatial and object but not verbal working memory using the n-back task

Sex-related differences have been reported for performance and neural substrates on some working memory measures that carry a high cognitive load, including the popular n-back neuroimaging paradigm. Despite some evidence of a sex effect on the task, the influence of sex on performance represents a potential confound in neuroimaging research. The present study investigated sex-related differences in verbal, spatial, and common object versions of the high cognitive load "n-back" working memory task. Eighteen male and 18 female undergraduates completed all 3 versions of the task. A mixed ANOVA, with Sex (male and female) as the between-subjects factor and Condition (verbal, spatial, and object) as the within-subjects repeated measure revealed that males were significantly more accurate than females on the spatial and object versions of the n-back task and performed equivalently to females on the verbal version of the task. Although the expected female advantage for verbal working memory was not found using this effortful n-back task, these results support a male advantage for high cognitive load spatial and object working memory. Future research should take into account the influence of sex on performance of the n-back task, and examine sex-related differences in working memory using other paradigms.     

Intelligence and spatiotemporal patterns of event-related desynchronization (ERD)

Recently, several studies have reported negative associations between brain activity under cognitive load and psychometric intelligence. The position emission tomography (PET) used in these studies allows a high spatial resolution, but it does not permit an assessment of the temporal course of cerebral activation. Therefore, this study examined the relationship between psychometric intelligence (determined by Raven's Advanced Progressive Matrices) and spatiotemporal patterns of cortical activation. Seventeen university students performed an elementary cognitive task, the Sentence Verification Test (SVT), during which the electroencephalogram (EEG) was recorded. In the EEG, the event-related desynchronization (ERD) was quantified, which can be interpreted as a correlate of cortical activation. Lower IQ participants displayed a comparatively unspecific cortical activation increasing with time, whereas higher IQ participants were characterized by a temporal development of activation in those cortical regions that are required for task performance, resulting in less overall activation as compared to the lower IQ participants. These findings support the hypothesis of a more efficient use of the brain in higher IQ individuals.     

An fMRI study of sex differences in regional activation to a verbal and a spatial task

Sex differences in cognitive performance have been documented, women performing better on some phonological tasks and men on spatial tasks. An earlier fMRI study suggested sex differences in distributed brain activation during phonological processing, with bilateral activation seen in women while men showed primarily left-lateralized activation. This blood oxygen level-dependent fMRI study examined sex differences (14 men, 13 women) in activation for a spatial task (judgment of line orientation) compared to a verbal-reasoning task (analogies) that does not typically show sex differences. Task difficulty was manipulated. Hypothesized ROI-based analysis documented the expected left-lateralized changes for the verbal task in the inferior parietal and planum temporal regions in both men and women, but only men showed right-lateralized increase for the spatial task in these regions. Image-based analysis revealed a distributed network of cortical regions activated by the tasks, which consisted of the lateral frontal, medial frontal, mid-temporal, occipitoparietal, and occipital regions. The activation was more left lateralized for the verbal and more right for the spatial tasks, but men also showed some left activation for the spatial task, which was not seen in women. Increased task difficulty produced more distributed activation for the verbal and more circumscribed activation for the spatial task. The results suggest that failure to activate the appropriate hemisphere in regions directly involved in task performance may explain certain sex differences in performance. They also extend, for a spatial task, the principle that bilateral activation in a distributed cognitive system underlies sex differences in performance.     

Intelligence is differentially related to neural effort in the task-positive and the task-negative brain network

Previous studies on individual differences in intelligence and brain activation during cognitive processing focused on brain regions where activation increases with task demands (task-positive network, TPN). Our study additionally considers brain regions where activation decreases with task demands (task-negative network, TNN) and compares effects of intelligence on neural effort in the TPN and the TNN. In a sample of 52 healthy subjects, functional magnetic resonance imaging was used to determine changes in neural effort associated with the processing of a working memory task. The task comprised three conditions of increasing difficulty: (a) maintenance, (b) manipulation, and (c) updating of a four-letter memory set. Neural effort was defined as signal increase in the TPN and signal decrease in the TNN, respectively. In both functional networks, TPN and TNN, neural effort increased with task difficulty. However, intelligence, as assessed with Raven's Matrices, was differentially associated with neural effort in the TPN and TNN. In the TPN, we observed a positive association, while we observed a negative association in the TNN. In terms of neural efficiency (i.e., task performance in relation to neural effort expended on task processing), more intelligent subjects (as compared to less intelligent subjects) displayed lower neural efficiency in the TPN, while they displayed higher neural efficiency in the TNN. The results illustrate the importance of differentiating between TPN and TNN when interpreting correlations between intelligence and fMRI measures of brain activation. Importantly, this implies the risk of misinterpreting whole brain correlations when ignoring the functional differences between TPN and TNN.     

Sex-related developmental differences in the lateralized activation of the prefrontal cortex and amygdala during perception of facial affect

The lateralization of cognitive abilities is influenced by a number of factors, including handedness, sex, and developmental maturation. To date, a small number of studies have examined sex differences in the lateralization of cognitive and affective functions, and in only few of these have the developmental trajectories of these lateralized differences been mapped from childhood through early adulthood. In the present study, a cross-sectional design was used with healthy children (n=7), adolescents (n= 12), and adults (n= 10) who underwent functional magnetic resonance imaging (fMRI) during a task that required perceiving fearful faces. Males and females differed in the asymmetry of activation of the amygdala and prefrontal cortex across the three age groups. For males, activation within the dorsolateral prefrontal cortex was bilateral in children, right lateralized in adolescents, and bilateral in adults, whereas females showed a monotonic relationship with age, with older females showing more bilateral activation than younger ones. In contrast, amygdala activation was similar for both sexes, with bilateral activation in children, right-lateralized activation in adolescents, and bilateral activation in adults. These results suggest that males and females show different patterns of lateralized cortical and subcortical brain activation across the period of development from childhood through early adulthood.     

Intelligence Level and the Allocation of Resources for Creative Tasks: A Pupillometry Study

This pupillometry study examined the relationship between intelligence and creative cognition from the resource allocation perspective. It was hypothesized that, during a creative metaphor task, individuals with higher intelligence scores would have different resource allocation patterns than individuals with lower intelligence scores. The study also examined the influence of intelligence in language and visuo-spatial domains on the resource allocation mechanism of verbal and visual creativity. The results suggested that individuals with higher intelligence scores allocated more cognitive resources for creative tasks than those with lower intelligence scores but not for non-creative tasks. The findings of this study support the view that creativity requires allocation of several cognitive faculties and may share underlying cognitive and neural mechanisms with intelligence. Domain-specific intelligence did not seem to play a significant role in the same domain, as individuals with higher scores in both domains showed similar resource allocation patterns. However, individuals with higher intelligence scores in the visuo-spatial domain generated more creative metaphorical interpretations in both verbal and visual creative metaphor tasks suggesting its importance in creative cognition.     

A Method for the Measurement of the Self-Concept of Children in the Third Grade

Fifty-five males and 38 females were administered a self-rating scale which allowed self and typical-student estimates of intelligence, motivation, and achievement. Males and females gave similar self-estimates of intelligence, although compared to the males, the females rated their motivation and achievement higher. Both males and females regarded the typical female student as more intelligent, more motivated, and more academically successful than the typical male student. A sex difference was observed on self versus typical-student-of-the-same-sex ratings. On noncollege-related personality dimensions, both males and females continue to share an unfavorable female stereotype.     

Sex differences in neural efficiency: Are they due to the stereotype threat effect?

The neural efficiency hypothesis postulates a more efficient use of brain resources in more intelligent people as compared to less intelligent ones. However, this relationship was found to be moderated by sex and task content. While the phenomenon of neural efficiency was previously supported for men when performing visuo-spatial tasks it occurred for women only when performing verbal tasks. One possible explanation for this finding could be provided by the well-studied phenomenon called stereotype threat. Stereotype threat arises when a negative stereotype of one’s own group is made salient and can result in behavior that confirms the stereotype. Overall, 32 boys and 31 girls of varying intellectual ability were tested with a mental rotation task, either under a stereotype exposure or a no-stereotype exposure condition while measuring their EEG. The behavioral results show that an activated negative stereotype not necessarily hampers the performance of girls. Physiologically, a confirmation of the neural efficiency phenomenon was only obtained for boys working under a no-stereotype exposure condition. This result pattern replicates previous findings without threat and thus suggests that sex differences in neural efficiency during visuo-spatial tasks may not be due to the stereotype threat effect.     

Working and long-term memory deficits in schizophrenia: is there a common prefrontal mechanism?

This study tested the hypothesis that dorsolateral prefrontal cortex deficits contribute to both working memory and long-term memory disturbances in schizophrenia. It also examined whether such deficits were more severe for verbal than nonverbal stimuli. Functional magnetic resonance imaging was used to assess cortical activation during performance of verbal and nonverbal versions of a working memory task and both encoding and recognition tasks in 38 individuals with schizophrenia and 48 healthy controls. Performance of both working memory and long-term memory tasks revealed disturbed dorsolateral prefrontal cortex activation in schizophrenia, although medial temporal deficits were also present. Some evidence was found for more severe cognitive and functional deficits with verbal than nonverbal stimuli, although these results were mixed.     

Differences in induced brain activity during the performance of learning and working-memory tasks related to intelligence

Thirteen high intelligent (H-IQ) and 13 low intelligent (L-IQ) individuals solved two figural working-memory (WM) tasks and two figural learning tasks while their EEG was recorded. For the WM tasks, only in the theta band group related differences in induced event-related desynchronization/synchronization (ERD/ERS) were observed. L-IQ individuals displayed greater theta synchronization in the later phases of task completion (1000-2000 ms) as compared to H-IQ individuals. For the learning tasks group related differences in the three alpha bands were observed. In the upper alpha band L-IQ individuals showed greater ERD in the frontal brain areas, whereas H-IQ individuals displayed greater ERD in the parieto-occipital brain areas.     

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.     

Handedness and sex differences in hemispheric asymmetry

A study was designed to assess the contributions of the factors of sex and familial history to cerebral dominance, where cerebral dominance was inferred from laterality on a dichotic listening task. The 144 subjects were selected from a larger sample on the basis of handedness, sex, and familial history of sinistrality, and tested on a task involving the dichotic presentation of CV syllables. Analysis of the data indicated that in female subjects, the presence of familial sinistrality increased the likelihood that they present atypical left-ear superiorities, while in males the converse was the case. Moreover, there was a significant sex difference overall, such that males were more clearly lateralized than females. A review of other dichotic listening studies provided support for the reliability of this sex difference for dichotic tasks using verbal material. A review of the clinical literature indicated that the hypothesis of a sex difference is at least tenable and merits further investigation. However, the possibility that there is a sex difference in the cognitive strategy used in dichotic listening cannot be ruled out.     

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.     

Strategy Induction Enhances Creativity in Figural Divergent Thinking

Instructional effects in creative‐thinking tasks are important to understand in order to promote creative performance of individuals. In divergent‐thinking tasks, for example, instructional and strategic enhancement effects have been extensively studied for verbal tasks. However, while studies on instructional enhancement effects on creative drawing tasks exist, it is surprising that strategy enhancement in figural divergent thinking is still underresearched. In this study, we used a strategy manipulation approach to reassess the role of executive strategy implementation and the moderating role of an indicator of fluid intelligence, figural analogical reasoning, in two types of figural divergent‐thinking tasks (abstract vs. concrete). The sample comprised N = 75 high‐school students. Importantly, we found strategic enhancement effects by combining strategy instructions with a prompt to “be creative.” This combined instruction was contrasted with a standard instruction, and main effects were found for overall, concrete, and abstract creativity. Moreover, we found in a regression analysis a main effect for figural analogical reasoning on overall creativity and creativity for only the concrete object tasks. An expected interaction effect of instruction and figural analogical reasoning was not found. As another addition, the role of current motivation in figural divergent thinking was explored.     

The Neural Bases of Strategy and Skill in Sentence–Picture Verification

This experiment used functional Magnetic Resonance Imaging to examine the relation between individual differences in cognitive skill and the amount of cortical activation engendered by two strategies (linguistic vs. visual–spatial) in a sentence–picture verification task. The verbal strategy produced more activation in language-related cortical regions (e.g., Broca's area), whereas the visual–spatial strategy produced more activation in regions that have been implicated in visual–spatial reasoning (e.g., parietal cortex). These relations were also modulated by individual differences in cognitive skill: Individuals with better verbal skills (as measured by the reading span test) had less activation in Broca's area when they used the verbal strategy. Similarly, individuals with better visual–spatial skills (as measured by the Vandenberg, 1971, mental rotation test) had less activation in the left parietal cortex when they used the visual-spatial strategy. These results indicate that language and visual–spatial processing are supported by partially separable networks of cortical regions and suggests one basis for strategy selection: the minimization of cognitive workload.     

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.     

The neural bases of strategy and skill in sentence-picture verification

This experiment used functional Magnetic Resonance Imaging to examine the relation between individual differences in cognitive skill and the amount of cortical activation engendered by two strategies (linguistic vs. visual-spatial) in a sentence-picture verification task. The verbal strategy produced more activation in language-related cortical regions (e.g., Broca's area), whereas the visual-spatial strategy produced more activation in regions that have been implicated in visual-spatial reasoning (e.g., parietal cortex). These relations were also modulated by individual differences in cognitive skill: Individuals with better verbal skills (as measured by the reading span test) had less activation in Broca's area when they used the verbal strategy. Similarly, individuals with better visual-spatial skills (as measured by the Vandenberg, 1971, mental rotation test) had less activation in the left parietal cortex when they used the visual-spatial strategy. These results indicate that language and visual-spatial processing are supported by partially separable networks of cortical regions and suggests one basis for strategy selection: the minimization of cognitive workload.     

Does g variance change in adulthood? Testing the age de-differentiation hypothesis across sex

In the last decade, changes in the structure of intelligence across the life-span has become a central topic in the research on human intelligence. One of the main hypotheses that has arisen to account for such changes has been the age de-differentiation hypothesis [Balinsky, Genetic Psychology Monographs 23 1941, 191]. It predicts an increase in the importance of g, and a decrease in the number and importance of the lower-order abilities from early maturity to senescence. Despite of the research effort to test this hypothesis, no study has ever been conducted controlling by sex. For that purpose, males and females of the Spanish standardisation sample of the WAIS-III were analysed separately. Results show that the importance of g does not change with age irrespective of sex. Thus, the age de-differentiation hypothesis is rejected for both males and females. The indifferentiation hypothesis is supported as a more appropriate view of the changes in the structure of intelligence across adulthood.     

Stereotypes and steroids: using a psychobiosocial model to understand cognitive sex differences

To further our understanding of cognitive sex differences, we studied the relationship between menstrual phase (via serum estradiol and progesterone levels) and cognitive abilities and cognitive performance in a sample of medical students in eastern Turkey. As expected, we found no sex differences on the Cattell "Culture Fair Intelligence Test" (a figural reasoning test), with females scoring significantly higher on a Turkish version of the Finding A's Test (rapid word knowledge) and males scoring significantly higher on a paper-and-pencil mental rotation test. The women showed a slight enhancement on the Finding A's Test and a slight decrement in Cattell scores during the preovulatory phase of their cycle that (probably) coincided with a rise in estrogen. There were also small cycle-related enhancements in performance for these women on the mental rotation test that may reflect cyclical increases in estrogen and progesterone. Additional analyses showed an inverted U-shaped function in level of estradiol and the Cattell Test. Finally, for women who were tested on Day 10 of their menstrual cycle, there was a negative linear relationship between their Cattell scores and level of progesterone. Stereotypes about the cognitive abilities of males and females did not correspond to performance on the mental rotation or Finding A's Test, so the sex-typical results could not be attributed to either stereotype threat or stereotype activation. For practical purposes, hormone-related effects were generally small. Variations over the menstrual cycle do not provide evidence for a "smarter" sex, but they do further our understanding of steroidal action on human cognitive performance.