Adult IQ Research Articles

Subcortical intelligence: caudate volume predicts IQ in healthy adults.

This study examined the association between size of the caudate nuclei and intelligence. Based on the central role of the caudate in learning, as well as neuroimaging studies linking greater caudate volume to better attentional function, verbal ability, and dopamine receptor availability, we hypothesized the existence of a positive association between intelligence and caudate volume in three large independent samples of healthy adults (total N = 517). Regression of IQ onto bilateral caudate volume controlling for age, sex, and total brain volume indicated a significant positive correlation between caudate volume and intelligence, with a comparable magnitude of effect across each of the three samples. No other subcortical structures were independently associated with IQ, suggesting a specific biological link between caudate morphology and intelligence.

A closer look at the role of parenting-related influences on verbal intelligence over the life course: Results from an adoption-based research design

The association between family/parenting and offspring IQ remains the matter of debate because of threats related to genetic confounding. The current study is designed to shed some light on this association by examining the influence of parenting influences on adolescent and young adult IQ scores. To do so, a nationally representative sample of youth is analyzed along with a sample of adoptees. The sample of adoptees is able to more fully control for genetic confounding. The results of the study revealed that there is only a marginal and inconsistent influence of parenting on offspring IQ in adolescence and young adulthood. These weak associations were detected in both the nationally representative sample and the adoptee subsample. Sensitivity analyses that focused only on monozygotic twins also revealed no consistent associations between parenting/family measures and verbal intelligence. Taken together, the results of these statistical models indicate that family and parenting characteristics are not significant contributors to variation in IQ scores. The implications of this study are discussed in relation to research examining the effects of family/parenting on offspring IQ scores.

Impaired IQ and academic skills in adults who experienced moderate to severe infantile malnutrition: A 40-year study

ObjectivesTo evaluate IQ and academic skills in adults who experienced an episode of moderate-to-severe infantile malnutrition and a healthy control group, all followed since childhood in the Barbados Nutrition Study.MethodsIQ and academic skills were assessed in 77 previously malnourished adults (mean age = 38.4 years; 53% male) and 59 controls (mean age = 38.1 years; 54% male). Group comparisons were carried out by multiple regression and logistic regression, adjusted for childhood socioeconomic factors.ResultsThe previously malnourished group showed substantial deficits on all outcomes relative to healthy controls (P < 0.0001). IQ scores in the intellectual disability range (< 70) were nine times more prevalent in the previously malnourished group (odds ratio = 9.18; 95% confidence interval = 3.50–24.13). Group differences in IQ of approximately one standard deviation were stable from adolescence through mid-life.DiscussionModerate-to-severe malnutrition during infancy is associated with a significantly elevated incidence of impaired IQ in adulthood, even when physical growth is completely rehabilitated. An episode of malnutrition during the first year of life carries risk for significant lifelong functional morbidity.

Early Childhood Stimulation Benefits Adult Competence and Reduces Violent Behavior

An estimated 178 million children younger than 5 years in developing countries experience linear growth retardation and are unlikely to attain their developmental potential. We aimed to evaluate adult benefits from early childhood stimulation and/or nutritional supplementation in growth-retarded children. In Kingston, Jamaica, 129 growth-retarded children aged 9 to 24 months took part in a 2-year trial of nutritional supplementation (1 kg milk-based formula per week) and/or psychosocial stimulation (weekly play sessions to improve mother-child interaction). We assessed IQ, educational attainment, and behavior at 22 years old in 105 participants. We used multivariate regressions, weighted to adjust for loss to follow-up, to determine treatment benefits. We found no significant benefits from supplementation. Participants who received stimulation reported less involvement in fights (odds ratio: 0.36 [95% confidence interval (CI) 0.12-1.06]) and in serious violent behavior (odds ratio: 0.33 [95% CI: 0.11-0.93]) than did participants with no stimulation. They also had higher adult IQ (coefficient: 6.3 [95% CI: 2.2-10.4]), higher educational attainment (achievement, grade level attained, and secondary examinations), better general knowledge, and fewer symptoms of depression and social inhibition. Early psychosocial intervention had wide-ranging benefits in adulthood that are likely to facilitate functioning in everyday life. The reductions in violent behavior are extremely important given the high levels of violence in many developing countries. The study provides critical evidence that early intervention can lead to gains in adult functioning.

196 Widespread White Matter Damage is Seen on DTI in Young Adults Born Preterm with Very Low Birth Weight (VLBW)

Background and aims: Perinatal brain injury in very low birth weight (VLBW) preterms is associated with permanent changes in white matter integrity and connectivity, and to neurodevelopmental problems including cognitive deficits. The aim of study was to investigate whether being born with VLBW leads to white matter damage that persist into adulthood, and to examine the relationship between white matter integrity and perinatal data and IQ in the VLBW group. Methods: Forty-nine VLBW young adults and 59 term controls were scanned at 1.5 T at ages 18-22 with DTI. Voxelwise maps of fractional anisotropy (FA) were calculated and Tract-Based Spatial Statistics was carried out to test for voxelwise differences between groups. Cognitive function was assessed with WAIS-III. The relationships between FA and total IQ and perinatal variables were explored. Results: In VLBW adults all major central and posterior white matter tracts had reduced FA, mainly caused by an increase in the two lowest eigenvalues. FA correlated positively with birth weight and negatively with number of days on mechanical ventilator and in NICU. More than half of the VLBW subjects obtained a subnormal IQ score. The FA-IQ correlation analyses demonstrated positive correlations between FA and IQ in regions including corpus callosum and long and short association tracts. Conclusions: Preterm birth with VLBW results in long-term irreversible changes in white matter microstructure that relate to inferior IQ in VLBW young adults. Lower birth weight and perinatal problems seem to have permanent negative effects on white matter integrity.

IQ in Early Adulthood and Mortality By Middle Age

High premorbid IQ test scores are related to a reduced rate of later total mortality, although little is known about the shape of this association (ie, dose-response versus threshold), or the role of mediating and confounding factors in explaining it. Additionally, the link between IQ and cause-specific mortality has been little explored.A cohort of over 1 million Swedish men who underwent IQ testing at military service conscription at about 18 years of age was followed for mortality experience until middle age.An average of 20 years of follow-up gave rise to 14,498 deaths in an analytical sample of 994,262. In basic analyses adjusting for age, year of birth, and conscription testing center, lower IQ scores were associated with an elevated risk of all-cause mortality (HRper 1-SD decrease in IQ; 1.32; 95% confidence interval = 1.30-1.34). This relation was incremental across the full IQ range, and was robust to adjustment for indicators of childhood social circumstances. The association did not appear to be mediated by factors measured concurrent with IQ (blood pressure, body mass index, or cigarette smoking), nor was it attributable to reverse causality. However, controlling for education (a close correlate of IQ) led to marked attenuation. IQ was also associated with mortality from accidents, coronary heart disease, and suicides, but not cancer.In this large cohort we found a robust stepwise relation between early adult IQ and risk of total and accident mortality in men.

Growth of the Corpus Callosum in Adolescents Born Preterm

To examine the growth of the corpus callosum between adolescence and early adulthood in individuals who were born before 33 weeks' gestation (very preterm [VPT]) and its relation to neuropsychological function. A longitudinal cohort study of VPT individuals born between January 4, 1982, and December 29, 1984, and a term-born comparison group. A long-term follow-up study into perinatal predictors of outcome after preterm birth at University College Hospital, London. A total of 72 VPT and 34 term-born individuals were assessed in adolescence (aged 15 years) and in early adulthood (aged 19 years). Adult assessments took place between June 6, 2002, and October 23, 2004. Birth before 33 weeks' gestation. The cross-sectional area of 4 segments of the corpus callosum, measured on the midsagittal slice of high-resolution structural magnetic resonance images in adolescence and young adulthood. Total corpus callosum size increased in term and VPT groups, but growth was much greater in the VPT group (13.4% in the VPT group vs 3.3% in the term group). There were significant associations between adult performance IQ and growth of anterior (P = .001), midposterior (P = .009), and posterior (P = .009) segments in the VPT group. The corpus callosum grows dramatically in VPT adolescents, and this growth is associated with neuropsychological outcome. This may represent a delay of a normal maturational process in VPT individuals.

The Role of Adolescent IQ and Gender in the Use of Cognitive Support for Remembering in Aging

ABSTRACT The purpose of this study was to examine the role of adolescent IQ (AIQ) and gender in older adults' ability to use cognitive support to enhance memory. Subjects were 269 mid-1940s graduates of the same high school. Adolescent IQ scores were gathered from archives, and subjects' memory for words was tested with tasks that provided increasing cognitive support. Overall, subjects benefited from support; women recalled more words than men; and persons with a high AIQ remembered more words than persons with a lower AIQ. However, while all subjects showed gains from cognitive support, men with a lower AIQ performed worse than men with a high AIQ. Women's performance was not dependent on their AIQ. Analysis of qualitative memory indicators suggested that women and persons with a high AIQ had better encoding and retrieval operations. Men with a lower AIQ appear to be particularly vulnerable to memory deficits in aging. This may be due to low “cognitive reserve” or generally poorer episodic memory function.

Relationships between IQ and Regional Cortical Gray Matter Thickness in Healthy Adults

Prior studies show positive correlations between full-scale intelligence quotient (FSIQ) and cerebral gray matter measures. Few imaging studies have addressed whether general intelligence is related to regional variations in brain tissue and the associated influences of sex. Cortical thickness may more closely reflect cytoarchitectural characteristics than gray matter density or volume estimates. To identify possible localized relationships, we examined FSIQ associations with cortical thickness at high spatial resolution across the cortex in healthy young adult (age 17-44 years) men (n = 30) and women (n = 35). Positive relationships were found between FSIQ and intracranial gray and white matter but not cerebrospinal fluid volumes. Significant associations with cortical thickness were evident bilaterally in prefrontal (Brodmann's areas [BAs] 10/11, 47) and posterior temporal cortices (BA 36/37) and proximal regions. Sex influenced regional relationships; women showed correlations in prefrontal and temporal association cortices, whereas men exhibited correlations primarily in temporal-occipital association cortices. In healthy adults, greater intelligence is associated with larger intracranial gray matter and to a lesser extent with white matter. Variations in prefrontal and posterior temporal cortical thickness are particularly linked with intellectual ability. Sex moderates regional relationships that may index dimorphisms in cognitive abilities, overall processing strategies, or differences in structural organization.

The prediction, from infancy, of adult IQ and achievement

Young adults, originally tested as infants for their ability to process information as measured by selective attention to novelty (an operational definition of visual recognition memory), were revisited. A current estimate of IQ was obtained as well as a measure of academic achievement. Information processing ability at 6–12 months was predictive of adult IQ and of academic achievement with coefficients of .34 and .32, and coefficients corrected for unreliability of .59 and .53, respectively. The present results support and extend earlier studies indicating the continuity of intelligence from infancy to adolescence and illustrate the validity of early measures of recognition memory based on selective attention to novelty for the long‐term prediction of achievement.

From the Cradle to the Labor Market? The Effect of Birth Weight on Adult Outcomes

Lower birth weight babies have worse outcomes, both short-run in terms of one-year mortality rates and longer run in terms of educational attainment and earnings. However, recent research has called into question whether birth weight itself is important or whether it simply reflects other hard-to-measure characteristics. By applying within twin techniques using an unusually rich dataset from Norway, we examine the effects of birth weight on both short-run and long-run outcomes for the same cohorts. We find that birth weight does matter; despite short-run twin fixed effects estimates that are much smaller than OLS estimates, the effects on longer-run outcomes such as adult height, IQ, earnings, and education are significant and similar in magnitude to OLS estimates.

The use of word-reading to estimate “premorbid” ability in cognitive domains other than intelligence

Diagnostic neuropsychological assessment requires the clinician to estimate a patient's premorbid abilities. Word reading tests, such as the National Adult Reading Test-Revised (NART-R), provide reasonably accurate estimates of premorbid IQ, but their capacity to benchmark other premorbid cognitive abilities remains unclear. In this extension of an earlier report, we administered the NART-R, an abbreviated Wechsler Adult Intelligence Scale (WAIS-R or WAIS-III), and 26 other cognitive measures to 322 reasonably healthy adults. While NART-R performance correlated robustly (rs > or = .72) with concurrent Verbal and Full Scale IQ, its correlation with all other cognitive measures was significantly lower. Thus, while it is appealing to use word reading as a proxy for premorbid functioning in other cognitive domains, the NART-R has limited utility for this because it does not predict current performance on other cognitive tests as well as it predicts IQ in healthy adults.

Concurrent Validity of Social Subtype and IQ after Early Intensive Behavioral Intervention in Children with Autism: A Preliminary Investigation

Three subtypes of autism based on social style have been proposed by Wing: active-but-odd, passive, or aloof. Previous research has shown evidence of an association between IQ and Wing subtype in untreated children and adults. Because IQ changes can accompany behavioral treatment, but often only for a subset of children, social subtype may be related to treatment responsiveness. We administered a social subtyping measure, the Wing Subgroups Questionnaire (WSQ), at various points in treatment to younger children than previously studied with autism in early, intensive behavioral intervention (EIBI). Thirty-seven children in EIBI (aged 39-71 months, amount of EIBI 0-44 months) were assessed to determine whether Wing's three proposed subtypes were found in this sample and whether subtypes were associated with current IQ and change in IQ after a period of EIBI. Results confirmed that all three subtypes were present and correlated with IQ after a period of intervention, as well as with change in IQ. Participants classified as aloof had significantly lower IQ scores and changes in IQ after EIBI than other children. Future studies should extend these findings by examining whether social subtype at pretreatment predicts EIBI outcome.

The relationship between age and IQ in adults with Williams syndrome.

The relationship between age and IQ was evaluated in a cross-sectional sample of 80 individuals with Williams syndrome (17 to 52 years). The relationship between age and WAIS-R subtest scores was such that increases and decreases in raw scores occurred at a rate sufficient to maintain stability of age-corrected scaled scores, indicating a developmental trajectory similar to that of the WAIS-R normative sample. Despite stability of age- corrected scaled scores with age, increased age was related to higher Performance IQ. This disparity, which occurs during the conversion of sums of scaled scores to IQs, may be unique to the WAIS-R. Although Performance IQ increased with age, results imply that the overall IQ of an adult with Williams syndrome will likely remain stable.

Stranger in the Nest

Stranger in the Nest David B. Cohen John Wiley and Sons Ltd John Wiley & Sons Inc, 1999, ISBN: 0471319228 Where do children's (and adults) personality, intelligence and character come from? Many questions of social policy, such as the origins and cures for poverty, depend on this question. Other questions anthropologists care about, such as how much can differences in cultural rearing patterns affect children's behavior (and hence their behavior when they become adults) depend on this. Thus, this is more than a book about parenting. How often do parents, having tried to raise the perfect child, one that reflects their values and goals, find that they have a "Stranger in the Nest", a child that turns out not to be one that reflects their values (including those of their culture) and desires? This happen often, and explain the title of the new book by University of Texas psychologist, David B. Cohen. The basic message of the book is given by the sub-title "Do Parents Really Shape their Child's Personality, Intelligence, or Character", with the answer a resounding No. Instead the book emphasizes the role of genetic and pre-natal events in shaping intelligence and personality. The book puts the emphasis on the good news for parents whose children have turned out other than as they would wish. It points out how many diseases and character faults were once blamed on poor parenting, but are now regarded as due to biological causes that parents can not be blamed for. The evidence for these conclusions comes from family studies, especially those of twins and adopted children. Cohen also points to the common observation that siblings, even same sex siblings, are radically different, both in personality and intelligence (sibling IQ differences average 12 points, which is 70% of the 18 point difference among children randomly selected from the same population). This is hard to explain by traditional social rearing theories, since parents usually raise their children in the same way. Yet it is easily explained by a genetic theory (perhaps supplemented by there being a random component in development, such as Miller 1997 has proposed). Some of best-documented genetic effects are for intelligence. Behavior genetics makes it possible to partition the environmental influence into that due to being reared in the same family (referred to as shared variance) and that due to other causes. One of the most striking findings is that the familial influences are so weak. Identical twins raised apart correlate about .75, while those reared together correlate .85. This suggests the effect of being reared together given identical genes is only .1, really quite small. As small as this is, studies of the IQ resemblance of unrelated children adopted into the same household show that they have essentially zero IQ, resemblance. This suggests that the effect of being reared in the same family is essentially zero. Most of the environmental effects documented (and behavior genetic methods do prove that there are environmental effects) appear to be due to things that siblings within the same family do not share. (Rowe 1994 presents much evidence for this). Supporting evidence for the role of genes is provided by many findings. Brain size correlates with IQ; ability tests done at 6 months (before most environmental influences have had a chance to exercise their effects) correlate with childhood IO; adult IQ correlates with the biological relatives of adoptees, but not with that of the adoptive parents, and IQ correlates with reaction times. For more on these correlations see Miller's (1999) review and summary of Jensen's (1998) recent book in this journal, or the review and summary (Miller 1996) of Brand's book (Brand, 1996) also called The g Factor. Interestingly, the publisher of Cohen's book is the same Wiley that withdrew Brand's book from the book stores, apparently because it discussed scientific facts about racial differences in intelligence they did not want discussed. …

EARLY SPEECH DELAY AND HEPATITIS AS PRESENTING SIGNS OF HOMOCYSTINURIA

89 Homocystinuria Type I (HCU), the most common inborn error of methionine metabolism, is usually diagnosed on the basis of classical phenotypic findings of ectopia lentis, marfanoid features, seizure disorder or mental retardation. The diagnosis of HCU is rarely made in the first five years of life unless by neonatal screening. We report a three-year-old male who was referred to hepatology clinic for elevated liver transaminases and was diagnosed with HCU based on the presentation of hepatitis and mild neurological abnormalities. The patient was generally well. He had achieved normal developmental milestones in the first year of life and his present cognitive social gross motor, fine motor, and receptive language skills were normal for age. He had however been previously diagnosed with expressive language delay and sensory integration dysfunction. The elevation of his liver enzymes had been detected during a routine screen. On physical exam the patient measured in the 95th percentile for height, weight and head circumference. He had an otherwise normal exam, including his neurological exam. Laboratory tests revealed that over a 6-month period, the patient's ALT had ranged between 77 to 173 IU/L, AST ranged between 57-88 IU/L. GGTP, bilirubin and albumin were within normal limits. Screening for hepatitis A, B, C, α-1 antitrypsin deficiency and Wilson's disease were all negative. His anti-nuclear antibody was negative and an anti-smooth muscle antibody was positive at a dilution of 1:160. Liver histology revealed microvesicular steatosis and mild periportal fibrosis. Electron microscopy of his liver tissue revealed hypertrophy of the smooth, endoplasmic reticulum and enlarged mitochondria with irregular contours, hallmarks of HCU. Amino acid studies of blood and urine were diagnostic of HCU. A trial of pyridoxine therapy was unsuccessful, however on a low methionine diet and oral betaine the patient's speech improved slightly. Conclusion: It is important to consider inborn errors of metabolism in the differential diagnosis of a patient with abnormal liver function tests and even a mild, isolated developmental delay or learning disability. In the case of HCU, early diagnosis and treatment is associated with improved clinical outcome, including higher adult IQ.

Cognitive Development following Prenatal Cocaine-Exposure • 1235

Prospective, blinded studies of children prenatally exposed to cocaine have not demonstrated significant cognitive impairment. However, prior studies have been limited by the early study age or small sample size. The aim of this preliminary report was to provide information on the cognitive outcome of 6-7 year old children prenatally exposed to cocaine. Subjects are singleton infants born to women extensively screened during pregnancy by research staff for alcohol, cigarette, cocaine and other drug use. As indicated, maternal and infant drug testing was ordered. Cocaine exposure was positive if history of lab was positive. Substance abuse was also quantified. Six years later, families were re-contacted. After informed consent, the child, primary caretaker and, when available, the biologic mother were tested. Child cognition was measured by the Weschler Preschool and Primary Scales of Intelligence (WPPSI). To reduce cultural bias, the triangles subscale of the Kaufman Assessment Battery for Children (K-ABC) was also included. This subtest is a good measure of simultaneous processing. Adult IQ was measured by the WAIS. Drug use since the child's birth was assessed by trained researchers using a structured interview. Results: The study sample consisted of 670 singleton children. Four subjects were known to have expired. Of those remaining, 36% could not be located. Only 8% refused participation. Testing was available for 57% of the sample (Cocaine exposed: N=137). Frequency of prenatal cocaine exposure was available for 314 children and highly correlated with postnatal use in the child's home (r=.35). However, urine testing of 150 children failed to identify any child positive for cocaine at follow-up. In the regression model, after controlling for gestational age, prenatal alcohol and cigarette exposure and the IQ of either the mother (86% cases), father(2%) or primary caretaker (12%), there was no significant relationship between either the binary or quantitative cocaine exposure and any of the child's cognitive scores. Conversely, prenatal alcohol exposure was negatively and significantly related to the WPPSI IQ (r=-.12, p=.023) and the K-ABC subscale approached significance (r=-.10, p=.08). An N of 314 provides sufficient power(.8) with α=.05 to detect a correlation of 0.16. Preliminary results of this NIDA-funded study suggest that cognition was negatively impacted by prenatal alcohol but not cocaine.

Genetic mediation of the correlation between peripheral nerve conduction velocity and IQ.

Variation in peripheral nerve conduction velocity (PNCV) and intelligence was studied in 18-year-old Dutch twins. It has been suggested that both brain nerve conduction velocity and PNCV are positively correlated with intelligence (Reed, 1984) and that heritable differences in nerve conduction velocity may explain part of the well-established heritability of intelligence. The relationship among IQ, obtained with the Wechsler Adult Intelligence Scale, and median nerve PNCV was examined in 159 twin pairs. Genetic analyses showed a heritability of 81% for IQ and 66% for onset PNCV. The small but significant phenotypic correlation between IQ and onset PNCV (.15) was entirely mediated by common genetic factors. Analyses of differences scores for PNCV of this study and PNCV from the same subjects collected at age 16 suggest that there might still be development in PNCV in this age interval. This maturation is highly controlled by genetic factors. It is suggested that variation in IQ that is associated with nerve conduction velocity becomes apparent only after the developmental processes in peripheral nerves are completed. This is in line with the suggestion of increasing heritability of IQ in adulthood.

Relationships of age and education to wechsler adult intelligence scale IQ values in Brain-Damaged and Non-Brain-Damaged Groups

Abstract Previous research (Reitan & Wolfson, 1995) has shown that age and education have a definite relationship among controls to scores on the General Neuropsychological Scale (GNDS), but minimal relationships among brain-damaged subjects. The present study investigated age and education relationships to WAIS VIQ, PIQ, and FSIQ values in brain-damaged and control groups, recognizing that these scores might differ from the GNDS in their sensitivity to brain damage as well as in their relationships to attribute variables. The findings yielded a complex set of results, with brain-damaged and non-brain-damaged groups being similar in some respects but different in others. In general, the results caution against the common practice of adjusting WAIS scores of brain-damaged subjects for age and education when the bases of the adjustments have been derived from non-brain-damaged controls.

Does education level determine the course of cognitive decline?

Many studies have implicated low education as a risk factor for cognitive impairment in elderly people. Findings are, however, inconsistent and the mechanism by which education level may intervene in senescent cognitive change is uncertain. The present study examines cognitive change over a 1-year period in 283 elderly persons manifesting recent subclinical deterioration in at least one area of cognitive functioning. The results suggest that the impact of both education level and young adult IQ on the degree of cognitive change over the year is greater in the older age groups. Secondary memory and language functions were found to be more resistant to decline in the high-education group, while attention, implicit memory and visuospatial skills are found to decline irrespective of education level.