Conduction velocity in a brain nerve pathway of normal adults correlates with intelligence level

Visual orientation discrimination skills are tightly linked with specific aspects of human intelligence

We investigate the notion that basic visual information is acting as a building block for more complex cognitive processes in humans. Specifically, we measured individual visual orientation discrimination thresholds to report significant correlations against the total standardised intelligence quotient (IQ), verbal-IQ and non-verbal IQ scores evaluated using the Wechsler Abbreviated Scale of Intelligence Second Edition (WASI-II) test battery comprising Verbal Reasoning, Block Design, Similarities and Matrix Reasoning subtests (N = 92). A multiple linear regression analysis showed that participants' performance in our visual discrimination task, could be explained only by individual scores in Verbal Reasoning which quantifies the ability to comprehend and describe words and Matrix Reasoning, which evaluates general visual processing skills including abstract and spatial perception. Our results demonstrate that low-level visual abilities and high-level cognitive processes are more tightly interwoven together than previously thought and this result could pave the way for further research on how cognition can be defined by basic sensory processes.

Information transmission velocity-based dynamic hierarchical brain networks

The brain functions as an accurate circuit that regulates information to be sequentially propagated and processed in a hierarchical manner. However, it is still unknown how the brain is hierarchically organized and how information is dynamically propagated during high-level cognition. In this study, we developed a new scheme for quantifying the information transmission velocity (ITV) by combining electroencephalogram (EEG) and diffusion tensor imaging (DTI), and then mapped the cortical ITV network (ITVN) to explore the information transmission mechanism of the human brain. The application in MRI-EEG data of P300 revealed bottom-up and top-down ITVN interactions subserving P300 generation, which was comprised of four hierarchical modules. Among these four modules, information exchange between visual- and attention-activated regions occurred at a high velocity, related cognitive processes could thus be efficiently accomplished due to the heavy myelination of these regions. Moreover, inter-individual variability in P300 was probed to be attributed to the difference in information transmission efficiency of the brain, which may provide new insight into the cognitive degenerations in clinical neurodegenerative disorders, such as Alzheimer's disease, from the transmission velocity perspective. Together, these findings confirm the capacity of ITV to effectively determine the efficiency of information propagation in the brain.

Conduction velocity along a key white matter tract is associated with autobiographical memory recall ability

Conduction velocity is the speed at which electrical signals travel along axons and is a crucial determinant of neural communication. Inferences about conduction velocity can now be made in vivo in humans using a measure called the magnetic resonance (MR) g-ratio. This is the ratio of the inner axon diameter relative to that of the axon plus the myelin sheath that encases it. Here, in the first application to cognition, we found that variations in MR g-ratio, and by inference conduction velocity, of the parahippocampal cingulum bundle were associated with autobiographical memory recall ability in 217 healthy adults. This tract connects the hippocampus with a range of other brain areas. We further observed that the association seemed to be with inner axon diameter rather than myelin content. The extent to which neurites were coherently organised within the parahippocampal cingulum bundle was also linked with autobiographical memory recall ability. Moreover, these findings were specific to autobiographical memory recall and were not apparent for laboratory-based memory tests. Our results offer a new perspective on individual differences in autobiographical memory recall ability, highlighting the possible influence of specific white matter microstructure features on conduction velocity when recalling detailed memories of real-life past experiences.

To What Extent Is General Intelligence Relevant to Causal Reasoning? A Developmental Study

To what extent general intelligence mechanisms are associated with causal thinking is unclear. There has been little work done experimentally to determine which developing cognitive capacities help to integrate causal knowledge into explicit systems. To investigate this neglected aspect of development, 138 children aged 5-11 studying at mainstream primary schools completed a battery of three intelligence tests: one investigating verbal ability (WASI vocabulary), another looking at verbal analogical (Verbal Analogies subset of the WRIT), and a third assessing non-verbal/fluid reasoning (WASI block design). Children were also interviewed over the course of three causal tasks (sinking, absorption, and solution), with the results showing that the developmental paths exhibited uneven profiles across the three causal phenomena. Children consistently found that explaining solution, where substances disappeared toward the end of the process, was more challenging. The confirmatory factor analyses suggested that the impact of cognitive ability factor in explicitly identifying causal relations was large. The proportion of the direct effect of general intelligence was 66% and it subsumed the variances of both verbal measures. Of this, 37% was the indirect effect of age. Fluid reasoning explained a further 28% of the variance, playing a unique role in causal explanation. The results suggested that, overall, cognitive abilities are substantially related to causal reasoning, but not entirely due to developmental differences in "g" during the age periods studied.

Visual N80 latency as a marker of neuropsychological performance in schizophrenia: Evidence for bottom-up cognitive models

OBJECTIVE

Cognitive deficits and visual impairment in the magnocellular (M) pathway, have been independently reported in schizophrenia. The current study examined the association between neuropsychological (NPS) performance and visual evoked potentials (VEPs: N80/P1 to M- and P(parvocellular)-biased visual stimuli) in schizophrenia and healthy controls.

METHODS

NPS performance and VEPs were measured in n = 44 patients and n = 34 matched controls. Standardized NPS-scores were combined into Domains and a PCA (Principal Component Analysis) generated Composite. Group differences were assessed via (M)ANOVAs, association between NPS and VEP parameters via PCA, Pearson's coefficient and bootstrapping. Logistic regression was employed to assess classification power.

RESULTS

Patients showed general cognitive impairment, whereas group differences for VEP-parameters were non-significant. In patients, N80 latency across conditions loaded onto one factor with cognitive composite, showed significant negative correlations of medium effect sizes with NPS performance for M/P mixed stimuli and classified low and high performance with 70% accuracy.

CONCLUSION

The study provides no evidence for early visual pathway impairment but suggests a heightened association between early visual processing and cognitive performance in schizophrenia.

SIGNIFICANCE

Our results lend support to bottom-up models of cognitive function in schizophrenia and implicate visual N80 latency as a potential biomarker of cognitive deficits in schizophrenia.

How neuroscience can inform the study of individual differences in cognitive abilities

Theories of human mental abilities should be consistent with what is known in neuroscience. Currently, tests of human mental abilities are modeled by cognitive constructs such as attention, working memory, and speed of information processing. These constructs are in turn related to a single general ability. However, brains are very complex systems and whether most of the variability between the operations of different brains can be ascribed to a single factor is questionable. Research in neuroscience suggests that psychological processes such as perception, attention, decision, and executive control are emergent properties of interacting distributed networks. The modules that make up these networks use similar computational processes that involve multiple forms of neural plasticity, each having different time constants. Accordingly, these networks might best be characterized in terms of the information they process rather than in terms of abstract psychological processes such as working memory and executive control.

Intelligence and specific cognitive functions in intellectual disability: implications for assessment and classification

PURPOSE OF REVIEW

Current diagnostic criteria for intellectual disability categorize ability as measured by IQ tests. However, this does not suit the new conceptualization of intellectual disability, which refers to a range of neuropsychiatric syndromes that have in common early onset, cognitive impairments, and consequent deficits in learning and adaptive functioning. A literature review was undertaken on the concept of intelligence and whether it encompasses a range of specific cognitive functions to solve problems, which might be better reported as a profile, instead of an IQ, with implications for diagnosis and classification of intellectual disability.

RECENT FINDINGS

Data support a model of intelligence consisting of distinct but related processes. Persons with intellectual disability with the same IQ level have different cognitive profiles, based on varying factors involved in aetiopathogenesis. Limitations of functioning and many biopsychological factors associated with intellectual disability are more highly correlated with impairments of specific cognitive functions than with overall IQ.

SUMMARY

The current model of intelligence, based on IQ, is of limited utility for intellectual disability, given the wide range and variability of cognitive functions and adaptive capacities. Assessing level of individual impairment in executive and specific cognitive functions may be a more useful alternative. This has considerable implications for the revision of the International Classification of Diseases and for the cultural attitude towards intellectual disability in general.

Comparing the Cognitive Ability Models of Spearman, Horn and Cattell, and Carroll

In recent years, researchers have focused on the development of hierarchical theories of intelligence. Flanagan and McGrew (1998) recently tested the appropriateness of Carroll's (1993a) hierarchical theory, the three-stratum theory, on the KAIT and WJ-R. Their results suggested that the KAIT is best interpreted from Carroll's theory rather than the test's recommended Gf-Gc theory, yet their sample had limited generalizability. The current study compared a single-factor model, Gf-Gc, and Carroll's hierarchical model on data from the KAIT and K-BIT standardization and validation sample. Results indicated that the Gf-Gc model was the only appropriate interpretive model for the KAIT and KAIT/K-BIT models.

Investigating the neural bases for intra-subject cognitive efficiency changes using functional magnetic resonance imaging

Several fMRI studies have examined brain regions mediating inter-subject variability in cognitive efficiency, but none have examined regions mediating intra-subject variability in efficiency. Thus, the present study was designed to identify brain regions involved in intra-subject variability in cognitive efficiency via participant-level correlations between trial-level reaction time (RT) and trial-level fMRI BOLD percent signal change on a processing speed task. On each trial, participants indicated whether a digit-symbol probe-pair was present or absent in an array of nine digit-symbol probe-pairs while fMRI data were collected. Deconvolution analyses, using RT time-series models (derived from the proportional scaling of an event-related hemodynamic response function model by trial-level RT), were used to evaluate relationships between trial-level RTs and BOLD percent signal change. Although task-related patterns of activation and deactivation were observed in regions including bilateral occipital, bilateral parietal, portions of the medial wall such as the precuneus, default mode network regions including anterior cingulate, posterior cingulate, bilateral temporal, right cerebellum, and right cuneus, RT-BOLD correlations were observed in a more circumscribed set of regions. Positive RT-BOLD correlations, where fast RTs were associated with lower BOLD percent signal change, were observed in regions including bilateral occipital, bilateral parietal, and the precuneus. RT-BOLD correlations were not observed in the default mode network indicating a smaller set of regions associated with intra-subject variability in cognitive efficiency. The results are discussed in terms of a distributed area of regions that mediate variability in the cognitive efficiency that might underlie processing speed differences between individuals.

Effects of age, intelligence and executive control function on saccadic reaction time in persons with intellectual disabilities

The current research aimed to clarify the influence of age, intelligence and executive control function on the central tendency and intraindividual variability of saccadic reaction time in persons with intellectual disabilities. Participants were 44 persons with intellectual disabilities aged between 13 and 57 years whose IQs were between 14 and 70. Executive control function was evaluated by a test of sustained simple motor action. To elicit saccades, a predictive visually guided saccade paradigm was used. Intelligence and executive control function were significantly associated with saccadic reaction time. The central tendency of saccadic reaction time was negatively correlated with intelligence. The more serious the degree of executive control dysfunction was, the larger the intraindividual variability of saccadic reaction time. It is thought that intelligence and executive control function have relatively independent influences on saccadic reaction time. However, there is a possibility that the increase of intraindividual variability in saccadic reaction time due to the problem of executive control function extends the central tendency of saccadic reaction time.

Can whole brain nerve conduction velocity be derived from surface-recorded visual evoked potentials?

Reed, Vernon, and Johnson [Reed, T. E., Vernon, P. A., & Johnson, A. M. (2004). Sex difference in brain nerve conduction velocity in normal humans. Neuropsychologia, 42, 1709-1714] reported that "nerve conduction velocity" (NCV) of visual transmission from retina to the primary visual area (V1) is significantly faster in males than females. The authors estimated the NCV by dividing head length (nasion-to-inion distance) by the latency of the well-known P100 component of the visual evoked potential (VEP). Here, we critically examine these metrics and we contend that knowledge of the underlying physiology of neural transmission across the initial stages of the visual processing hierarchy dictates that a number of their assumptions cannot be reasonably upheld. Alternative, and we believe, more parsimonious interpretations of the data are also proposed.

Sex difference in brain nerve conduction velocity in normal humans

Nerve conduction velocity (NCV), the speed at which impulses travel along nerves, has been extensively determined in human peripheral nerves because of its clinical utility. In contrast, almost no studies have been made of human brain NCV. We determined brain NCVs in the visual nerve pathway for 185 male and 200 female university students ages 18-25 years. In each of three independent test conditions, we found that the mean NCV of male students is about 4% faster than in females (P < or = 0.0001 for each condition). These male students also have a shorter reaction time in each of seven different RT tests than do females, even though, on the null hypothesis of equal NCVs, we would expect males to have longer RT times because of their greater physical size. Four of these comparisons are significant at or below the 0.001 level. These males also increase their NCVs with increasing age, in contrast to females. These sex differences in NCV parallel reported sex differences in age changes in white matter in the brain. These age changes may largely explain these NCV differences.

There are stable individual differences in performance variability, both from moment to moment and from day to day

Individual differences in decision speed have been regarded as direct reflections of a "primitive" functional neurophysiological characteristic, which affects performance on all cognitive tasks and so may be regarded as the "biological basis of intelligence", or of age-related changes in mental abilities. More detailed analyses show that variability within an experimental session (WSV) is a stable individual difference characteristic and that mean choice reaction times (CRTs) are gross summary statistics that reflect variability, rather than maximum speed of performance. A total of 98 people aged from 60 to 80 years completed 36 weekly sessions on six different letter categorization tasks. After effects of practice and of circadian variability had been eliminated, individuals with lower scores on the Cattell Culture Fair intelligence test had slower CRTs and greater WSV on all tasks. A simulation study showed that the greater WSVs of low Cattell scorers led directly to the significantly greater variability of their mean CRTs from session to session. However because CRTs on tasks co-varied from session to session it was apparent that, besides being affected by WSV, individuals' between-session variabilities (BSVs) also vary because of state changes that affect their performance from day to day. It seems that both variability in performance from trial to trial during a session and variability in average performance from day to day are correlated, stable, individual difference characteristics that vary inversely with intelligence test performance. Methodological consequences of these results for interpretations of age-related cognitive changes, for variability between as well as within individuals, for individual differences in decision speed, and for circadian variability in performance are discussed.

Central role of g in military pilot selection

The role of general cognitive ability (g) in the selection of military pilots is discussed. Four seminal issues that threaten the interpretation of the results of ability studies are introduced and examined. A brief history of the use of g in pilot selection is presented, going back to the World War I era. At that time, many countries used tests such as perception and reaction time, later shown to be mostly measures of g. The World War II era brought the age of the multiple aptitude batteries, and with it, the theory of differential abilities. However, most militaries still used highly g-saturated measures. More recently, an awareness of the prominence of g in job performance has led to a series of studies that showed the central role of g in predicting pilot success. In comparative analyses, g was found to be a better predictor of pilot criteria than specific abilities. However, some specific abilities or measures of job knowledge were found to increment the predictiveness of g. Several selection variables that appeared to measure characteristics other than g were found to measure, at least in some part, g. These include psychomotor tests and structured interviews. Finally, speculation on the future of the measurement of g is presented.

A Função Adverbial de "Inteligência": Definições e Usos em Psicologia

Não há consenso em psicologia sobre a natureza, definição e nível de análise nas investigações relacionadas ao conceito de inteligência. A análise do uso deste conceito na linguagem cotidiana indicou que o mesmo exerce função adverbial, a qual caracteriza uma ação como bem-sucedida. O conceito é usado em níveis diferentes, funcionando como um resumo adverbial das ações de um indivíduo de forma geral ou de suas habilidades específicas. Como "sucesso" é relativo a valores culturais, a definição de inteligência também depende da cultura. A função adverbial pode vir a explicar pelo menos parte das divergências e controvérsias encontradas em psicologia.

Correlations between ERP parameters and intelligence: a reconsideration

The present study investigated differences in ERP parameters related to intelligence. For that purpose 74 individuals (Intelligence: M=107; S.D.=12; range 73-135), of average creativity passively listened to two tones and performed two auditory, and two visual oddball tasks while their EEG was recorded. The approximate entropy parameters, peak latencies and amplitudes were determined. The correlation coefficients indicated that in the attended conditions, the more intelligent individuals showed more regular ERP waveforms than less intelligent individuals. It was further found that less intelligent individuals showed increased P300 latencies and reduced amplitudes. The differences were explained with a more specific engagement of neural networks in more intelligent individuals.

Contributions to the history of psychology: CXII. Intelligence, behavior genetics, and the Pioneer Fund

Since World War I, political controversies have complicated the long-standing debate on nature versus nurture, especially the question of the source of the observed mean difference in intelligence between white and black groups. The Pioneer Fund, one of the few nonprofit foundations making grants for study and research into human individual and group differences, has been widely and unfairly attacked by those who believe any such research jeopardizes political commitment to legal equality. The four main scholarly areas of research financially supported by Pioneer have been behavioral genetics, cognitive ability, demographic characteristics, and racial variation. This article provides a unique perspective on the history of the Pioneer Fund and some of the controversies that have taken place.

Human abilities

This chapter reviews recent literature, primarily from the 1990s, on human abilities. The review opens with a consideration of the question of what intelligence is, and then considers some of the major definitions of intelligence, as well as implicit theories of intelligence around the world. Next, the chapter considers cognitive approaches to intelligence, and then biological approaches. It proceeds to psychometric or traditional approaches to intelligence, and then to broad, recent approaches. The different approaches raise somewhat different questions, and hence produce somewhat different answers. They have in common, however, the attempt to understand what kinds of mechanisms lead some people to adapt to, select, and shape environments in ways that match particularly well the demands of those environments.

A Person–Process–Context–Time Approach to Understanding Intellectual Development

We argue that scientific psychology's twin foci on biology (person) and process can benefit from a broadening. Specifically, we show that including two additional foci—context and time—can add explanatory leverage to both the design and interpretation of scientific studies. We focus on research on intellectual development to illustrate our points. First, we briefly describe each of the four factors (person, process, context, and time), and we review studies that focus on each individual factor and its role in intellectual development. Next, we review studies that focus simultaneously on multiple factors. We illustrate how multifactor approaches reveal fine-grained differentiations that are not reducible to single factors. Finally, we describe a study that considers simultaneously all four factors, and we show how omitting any one of these factors from the design and analysis changes the interpretation of the data.

Neuroscience and human intelligence differences

Research into the biological bases of human intelligence differences is surveyed. Work on brain event-related potentials (ERPs) suggests that people with high IQ test scores: (1) show faster responses in some test conditions; (2) have ERP waveforms that can be distinguished from those of people with lower IQs; and (3) might have less variability in their ERPs. People with higher psychometric intelligence have, on average, larger brains, and possibly faster neural conduction speed. A few small functional brain-scanning studies suggest that, in healthy individuals, people who are of higher IQ have lower cerebral metabolic rates during mentally active conditions. This has led to the speculation that brighter people have more efficient brains. Despite some well-replicated findings in the search for the 'biology of human intelligence' there is a dearth of explanatory accounts to link cognitive performance differences with variance in brain mechanisms.

Correlations between nonverbal intelligence and peripheral nerve conduction velocity in right-handed subjects: sex-related differences

The speed hypothesis of intelligence was tested in relation to median nerve conduction velocity (NCV) in right-handed subjects. In total, NCV did not significantly correlate with IQ (Cattell's Culture Fair Intelligence test). The motor and sensory median NCVs correlated with IQ positively linearly in men and negatively linearly in women. These results supported the general, unqualified speed hypothesis of intelligence only for men. It was concluded that the conduction speed of the input-output channels of brain as an information processing unit may differentially contribute to nonverbal intelligence, depending upon sex. The male hormone, testosterone, was suggested to be the main factor responsible for sex-related differences in the IQ-NCV relationships.

The independent prediction of general intelligence by elementary cognitive tasks: genetic and environmental influences

Current theories of intelligence have, in some cases, begun to include elementary cognitive tasks. Behavioral genetic studies of intelligence have not taken these theories into account. The current study includes 135 MZ and 128 DZ twin pairs from the Western Reserve Twin Project. The 11 WISC-R subtests as well as 6 elementary cognitive tasks were employed. Using a Schmid-Leiman (1957) transformation, analyses indicate a four-group factor model, supported by a second-order general factor at both phenotypic and biometric levels. Results indicate that the general factor, group factors, and specific residuals are necessary when examining additive genetic variance. Common environmental variance can be collapsed into a single general factor.

Spearman's g: links between psychometrics and biology

Individual differences with respect to diverse tests of mental abilities that range in complexity from simple reaction time to abstract reasoning are all positively correlated in the population. The total covariance among all such tests can be analyzed into a number of uncorrelated components of variance, or factors, that, in terms of their generality, are hierarchical, with the most general factor, or g, at the apex. This g factor is common to every type of cognitive performance, whatever other ability factors may be involved (e.g., verbal, spatial, numerical, musical, etc.), and is the crucial factor in most tests' practical validity. Its correlations with various tests' heritability, inbreeding depression, heterosis, average evoked potentials, brain metabolism, and many other physical correlates indicate that as a product of evolution it is profoundly enmeshed with many organismic variables. A theory based on empirical evidence links g to neural processes involved in the speed and efficiency of information processing.