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PubMed2001

A genome-wide scan of 1842 DNA markers for allelic associations with general cognitive ability: a five-stage design using DNA pooling and extreme selected groups.

All measures of cognitive processes correlate moderately at the phenotypic level and correlate substantially at the genetic level. General cognitive ability (g) refers to what diverse cognitive processes have in common. Our goal is to identify quantitative trait loci (QTLs) associated with high g compared with average g. In order to detect QTLs of small effect size, we used extreme selected samples and a five-stage design with nominal alpha levels that permit false positive results in early stages but remove false positives in later stages. As a first step toward a systematic genome scan for allelic association, we used DNA pooling to screen 1842 simple sequence repeat (SSR) markers approximately evenly spaced at 2 cM throughout the genome in a five-stage design: (1) case-control DNA pooling (101 cases with mean IQ of 136 and 101 controls with mean IQ of 100), (2) case-control DNA pooling (96 cases with IQ > 160 and 100 controls with mean IQ of 102), (3) individual genotyping of Stage 1 sample, (4) individual genotyping of Stage 2 sample, (5) transmission disequilibrium test (TDT; 196 parent-child trios for offspring with IQ > 160). The over all Type I error rate is 0.000125, which robustly protects against false positive results. The numbers of markers surviving each stage using a conservative allele-specific directional test were 108, 6, 4, 2, and 0, respectively, for the five stages. A genomic control test using DNA pooling suggested that the failure to replicate the positive case-control results in the TDT analysis was not due to ethnic stratification. Several markers that were close to significance at all stages are being investigated further. Relying on indirect association based on linkage disequilibrium between markers and QTLs means that 100,000 markers may be needed to exclude QTL associations. Because power drops off precipitously for indirect association approaches when a marker is not close to the QTL, we are not planning to genotype additional SSR markers. Instead we are using the same design to screen markers such as cSNPs and SNPs in regulatory regions that are likely to include functional polymorphisms in which the marker can be presumed to be the QTL.

Adolescent↗
PubMed2004

Pupillary responses on the visual backward masking task reflect general cognitive ability.

Cognitive processing efficiency requires both an ability to attend to task-relevant stimuli with quickness and accuracy, also while filtering distracting or task-irrelevant stimuli. This study investigated cognitive processing efficiency by using pupillary responses as an index of attentional allocation to relevant target and irrelevant masks on a visual backward masking task. The relationship between attentional allocation on this task and general cognitive ability on the scholastic aptitude test (SAT) was examined in college students (n=67). A principle components analysis of the pupillary response waveform isolated a late component that appeared to index the attentional demands associated with processing masks on the backward masking task. This pupillary response index of wasteful resource allocation to the mask accounted for significant variance in SAT scores over and above that accounted for by socio-economic status and target detection accuracy scores. Consistent with the neural efficiency hypothesis, individuals who allocated more resources to processing irrelevant information performed more poorly on cognitive ability tests.

Adult↗
PubMed2006

Genetic variation in DTNBP1 influences general cognitive ability.

Human intelligence is a trait that is known to be significantly influenced by genetic factors, and recent linkage data provide positional evidence to suggest that a region on chromosome 6p, previously associated with schizophrenia, may be linked to variation in intelligence. The gene for dysbindin-1 (DTNBP1) is located at 6p and has also been implicated in schizophrenia, a neuropsychiatric disorder characterized by cognitive dysfunction. We report an association between DTNBP1 genotype and general cognitive ability (g) in two independent cohorts, including 213 patients with schizophrenia or schizo-affective disorder and 126 healthy volunteers. These data suggest that DTNBP1 genetic variation influences human intelligence.

Adult↗
PubMed2004

Scholastic Assessment or g? The relationship between the Scholastic Assessment Test and general cognitive ability.

There is little evidence showing the relationship between the Scholastic Assessment Test (SAT) and g (general intelligence). This research established the relationship between SAT and g, as well as the appropriateness of the SAT as a measure of g, and examined the SAT as a premorbid measure of intelligence. In Study 1, we used the National Longitudinal Survey of Youth 1979. Measures of g were extracted from the Armed Services Vocational Aptitude Battery and correlated with SAT scores of 917 participants. The resulting correlation was.82 (.86 corrected for nonlinearity). Study 2 investigated the correlation between revised and recentered SAT scores and scores on the Raven's Advanced Progressive Matrices among 104 undergraduates. The resulting correlation was.483 (.72 corrected for restricted range). These studies indicate that the SAT is mainly a test of g. We provide equations for converting SAT scores to estimated IQs; such conversion could be useful for estimating premorbid IQ or conducting individual difference research with college students.

Adolescent↗
PubMed2001

A high density of X-linked genes for general cognitive ability: a run-away process shaping human evolution?

The incidence of mental disability is 30% higher in males than in females. We have examined entries in the OMIM database that are associated with mental disability and for several other common defects. Our findings indicate that compared with the autosomes, the X chromosome contains a significantly higher number of genes that, when mutated, cause mental impairment. We propose that these genes are involved in the development of cognitive abilities and thus exert a large X-chromosome effect on general intelligence in humans. We discuss these conclusions with regard to the conservation of the vertebrate X-chromosomal linkage group and to human evolution.

Animals↗
PubMed1997

General cognitive abilities and patterns of adaptation: for Serial Color-Word Test norms based on reading times.

In a pool of 859 clinical and nonclinical Serial Color-Word Test protocols, significant positive correlations were observed between reading times on the Stroop task and measures of linear and nonlinear change. Especially nonlinear change, both within and between the five subtests, showed high correlations with reading times. To derive new time-related norms, the sample was divided into five time groups of the same size and stratified medians were calculated for each of the variables of the test. The new classification procedure should permit an assessment of patterns of adaptation less dependent on the general level of perceptual-cognitive functioning.

Adult↗
PubMed1995

General cognitive ability following unilateral and bilateral fetal ventral mesencephalic tissue transplantation for treatment of Parkinson's disease.

OBJECTIVE: To contrast the neuropsychological profiles of Parkinsonian patients, before and after fetal ventral mesencephalic tissue transplantation. DESIGN: Case series of personally examined patients. SETTING: Patients were evaluated by neurologists, neurosurgeons, and neuropsychologists as outpatients at a university hospital. PATIENTS: Fetal mesencephalic tissue was implanted in the right caudate nucleus of three patients and both nuclei of one patient. These patients were evaluated prior to surgery and at 12, 24, and 26 months postoperatively. RESULTS: Factor analysis of the test battery identified four statistically orthogonal test clusters. No statistically significant changes were identified postoperatively for clusters assessing verbal cognitive ability, nonverbal cognitive ability, and information-processing speed. An improvement of verbal memory cluster index was observed 12 months after surgery, and the improvement reached the level of statistical significance at 24 months after surgery. However, the verbal memory of all patients declined between 24 and 36 months after surgery. CONCLUSIONS: Fetal tissue transplantation to one or both caudate nuclei did not permanently arrest cognitive dysfunction. Although there is some evidence of improved cognitive ability after transplantation, it is improbable that normal cognitive function can be restored by this procedure because the impairments of cognitive ability associated with Parkinson's disease do not appear to originate solely from dopamine deficiency.

Adult↗
PubMed2002

Genetics and general cognitive ability (g).

Two recent articles in this journal made the case for the existence and importance of g and reviewed research on cognitive and psychophysical correlates of psychometric g. This review considers g from a genetic perspective. Multivariate genetic research indicates that g accounts for nearly all of the genetic variance of diverse psychometric cognitive tests (genetic g). Recent research suggests not only that elementary cognitive tasks are genetically linked to psychometric g but also that genetic g pervades these tasks. Contrary to the assumption of modularity that dominates cognitive science, genetic g exists in the mind as well as in psychometric tests.

Journal Article↗
PubMed2001

Genetics, environment and cognitive abilities: review and work in progress towards a genome scan for quantitative trait locus associations using DNA pooling.

BACKGROUND: Multivariate genetic research indicates that genetic effects on diverse cognitive abilities are general rather than specific or modular. General cognitive ability (g), a key factor in learning and memory, is among the most heritable behavioural traits. AIMS: To give a brief overview of quantitative genetic research on g and to describe initial results from a programme of research that aims to identify genes responsible for the substantial heritability of general cognitive ability. METHOD: The research uses a new technique called DNA pooling, which combines DNA from individuals within a group and makes it feasible to screen thousands of DNA markers for a systematic scan of the genome for associations between DNA markers and g. Two independent samples of children with very high g scores and two control samples of children with average g scores were compared in a systematic scan of 147 markers on chromosome 4 and 66 markers on chromosome 22. RESULTS: Three replicated associations on chromosome 4 were identified using DNA pooling and confirmed using individual genotyping. CONCLUSIONS: These first results of the application of DNA pooling in systematic analysis of allelic association are encouraging.

Adult↗
PubMed2006

Cognitive outcome and cyclo-oxygenase-2 gene (-765 G/C) variation in the preterm infant.

BACKGROUND: Cyclo-oxygenase (COX) inhibition by indomethacin does not result in an improvement in long-term neurocognitive outcome, despite reducing the incidence of both severe intraventricular haemorrhage and white matter injury visible on ultrasound. Diffuse brain injury after preterm birth may have inflammatory origins. These two points suggest that, in the preterm brain, COX inhibition may have a dominant proinflammatory or neuropathological role. The inducible form of the COX2 gene is polymorphic: the -765 C (rather than G) variant of the gene is associated with reduced COX2 activity. OBJECTIVE: To test the hypothesis that the C allele of COX2 is associated with worse neurodevelopmental outcomes after premature birth. OUTCOMES: Cerebral palsy, disability, Griffith's developmental quotient at 2 years and British Ability Scales-11 general cognitive ability and motor performance (movement assessment battery for children) at 5(1/2) years were compared with COX2 genotype. RESULTS: The C allele (GC 65 (31%), CC 3 (1%)) was independently associated with worse cognitive performance at 2 and 5(1/2) years: C allele mean (SEM) developmental quotient 92.7 (1.7), v GG 97.6 (1.5), p = 0.039; C allele mean (SEM) general cognitive ability, 94.3 (2.2) v GG 100.9 (1.7), p = 0.028. CONCLUSION: An antineuropathological role for COX2 in the preterm brain may help account for the lack of effect of indomethacin treatment in improving neurocognitive outcomes in children born preterm, despite reported reduction in apparent brain injury.

Alleles↗
PubMed1994

Variability and stability in cognitive abilities are largely genetic later in life.

The powerful quantitative genetic design of identical and fraternal twins reared apart (112 pairs) and matched twins reared together (111 pairs) was employed to assess the extent of genetic influence on individual differences in cognitive abilities during the last half of the life span. General cognitive ability yielded a heritability estimate of about .80 in two assessments 3 years apart as part of the Swedish Adoption/Twin Study of Aging. This is one of the highest heritabilities reported for a behavioral trait. Across the two ages, average heritabilities are about .60 for verbal tests, .50 for spatial and speed-of-processing tests, and .40 for memory tests. For general cognitive ability, the phenotypic stability across the 3 years is .92 and stable genetic factors account for nearly 90% this stability. These findings suggest that general cognitive ability is a reasonable target for research that aims to identify specific genes for complex traits.

Aging↗
PubMed2004

Interactions of biomedical and environmental risk factors for cognitive development: a preliminary study of sickle cell disease.

Sickle cell disease (SCD) is associated with a number of biopsychosocial risk factors for cognitive development. Understanding how these risk factors may interact is important for developing interventions for cognitive functioning. The authors assessed the cognitive abilities of children with SCD (n = 50) and related their performance to anemia severity, socioeconomic status (SES), and their interaction. Demographically matched peers without SCD (n = 36) served as a comparison group. Four areas of cognitive weakness were identified among children with SCD: general cognitive ability, crystallized ability, short-term memory, and processing speed. Anemia severity predicted general cognitive ability, crystallized ability, and processing speed. Interactions between anemia severity and SES were found for general cognitive ability and short-term memory. Disease effects in SCD appear to vary depending on the child's level of socioenvironmental risk. Biomedical interventions to benefit cognitive functioning may have different effects depending on whether additional socioenvironmental risk factors are present.

Adolescent↗
PubMed2006

Are deficits in executive sub-processes simply reflecting more general cognitive decline in schizophrenia?

BACKGROUND: Schizophrenia is associated with both global and specific cognitive deficits. We sought to investigate whether deficits in executive subcomponents differed in their relationship to global cognitive impairments. METHOD: 95 patients were classified according to pre-morbid and current general cognitive ability as having either (a) intact pre-morbid and current general cognitive ability; (b) intact pre-morbid but deteriorated current ability, and (c) deteriorated both pre-morbid and current cognitive ability. All patients completed measures of verbal and spatial working memory, sustained selective attention, attentional set sifting, and inhibitory control. RESULTS: Deficits on both measures of working memory were associated with general cognitive ability. None of the attentional control deficits observed were associated with general ability. Further, spatial working memory deficits were also associated with more severe negative symptoms. CONCLUSIONS: These results provide further evidence of the discreet nature of attentional deficits in schizophrenia. By contrast, this study suggests that working memory deficits may to some extent index more general cognitive decline. Awareness of such overlap is important for schizophrenia genetics studies where working memory measures has been used to index supposedly discreet aspects of cognitive dysfunction.

Adult↗
PubMed1999

Job complexity and employee substance use: the moderating effects of cognitive ability.

This study examines the extent to which individual's general cognitive ability influences relations between the complexity of their jobs and their use of four different substances: cigarettes, alcohol, marijuana, and cocaine. We tested this possibility using 1992 and 1982 data sets from the National Longitudinal Survey of Youth (Center for Human Resource Research 1993). The 1992 data set included 7,112 individuals and measures of all four substances. The 1982 set included 8,548 individuals and a measure of alcohol use only. Our results showed that for three of the substances (cigarettes, alcohol, and marijuana), individuals responded differently to job complexity as a function of their cognitive ability. Specifically, for individuals low in cognitive ability, the more complex their jobs, the greater their use of cigarettes, alcohol, and marijuana. On the other hand, for those with high cognitive ability, the more complex their jobs, the lower their use of these substances. Results also showed that cognitive ability had no significant impact on the association between job complexity and cocaine use. In sum, our findings suggest that providing employees with jobs that are compatible with their general cognitive ability may result in lower levels of licit and illicit substance use.

Adult↗
PubMed2001

Relative roles of cognitive ability and practical intelligence in the prediction of success.

Initial investigations into the construct of practical intelligence have identified a new general factor of practical intelligence (gp), which is believed to be independent of general cognitive ability. This construct, gp, is also believed to be a better predictor of success than cognitive ability, personality, or any combination of variables independent of gp. The existence of this construct and its independence from Spearman's g is, however, under debate. The purpose of the present study is to investigate both the relationship between gp and g and the relative roles of practical intelligence and cognitive ability in the prediction of success. The participants included 197 college students. Each completed both the Multidimensional Aptitude Battery and Sternberg and Wagner's measure of practical intelligence in academic psychology. The results of structural equation modeling support Sternberg and Wagner's assertion that practical intelligence and general cognitive ability are relatively independent constructs. Results of regression analysis, however, do not support their contention that practical intelligence is related to success after controlling for general cognitive ability. Implications of these results for research and theory on practical intelligence are discussed.

Adult↗