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Describes growing human health issues linked to exposure to a multiplicity of chemicals and mixtures. Impacts on the human brain, intelligence and mental disorders, autism, ADHD, depression, child and adult cancers, developmental diseases of children, sexual, gender and reproductive disorders, obesity and diabetes, ‘mystery’ disorders, re-emergence of ‘old’ conditions. The epigenetic curse. The case for precaution.
The previous themes reach into modern debates about freedom and necessity, which are still central in education and psychology today. Contributing to the rise of formal disciplines of developmental and child psychology, educational psychology, clinical psychology and cognitive psychology, as well as psychiatry, empirical approaches based on sense perception began in the mid-eighteenth century; but they are equally the outcome of broader religious and cultural influences. The book therefore concludes with an overview of the direct traces on the modern disciplines of the religious ideas discussed in earlier chapters: in Britain through David Hartley, Joseph Priestley and Francis Galton, and the nature-versus-nurture formula; and in France Hippolyte Taine, Alfred Binet (creator of the ‘mental age’ score, subsequently IQ measurement) and Jean Piaget himself.
The work of Ed Zigler spans decades of research all singularly dedicated to using science to improve the lives of children facing different challenges. The focus of this article is on one of Zigler's numerous lines of work: advocating for the practice of mental age (MA) matching in empirical research, wherein groups of individuals are matched on the basis of developmental level, rather than chronological age. While MA matching practices represented a paradigm shift that provided the seeds from which the developmental approach to developmental disability sprouted, it is not without its own limits. Here, we examine and test the underlying assumption of linearity inherent in MA matching using three commonly used IQ measures. Results provide practical constraints of using MA matching, a solution which we hope refines future clinical and empirical practices, furthering Zigler's legacy of continued commitment to compassionate, meaningful, and rigorous science in the service of children.
The etiology of schizophrenia (SZ) is proposed to include an interplay between a genetic risk for disease development and the biological environment of pregnancy and birth, where early adversities may contribute to the poorer developmental outcome. We investigated whether a history of birth asphyxia (ASP) moderates the relationship between intracranial volume (ICV) and intelligence in SZ, bipolar disorder (BD) and healthy controls (HC).
Two hundred seventy-nine adult patients (18–42 years) on the SZ and BD spectrums and 216 HC were evaluated for ASP based on information from the Medical Birth Registry of Norway. Participants underwent structural magnetic resonance imaging (MRI) to estimate ICV and intelligence quotient (IQ) assessment using the Wechsler Abbreviated Scale of Intelligence (WASI). Multiple linear regressions were used for analyses.
We found a significant three-way interaction (ICV × ASP × diagnosis) on the outcome variable, IQ, indicating that the correlation between ICV and IQ was stronger in patients with SZ who experienced ASP compared to SZ patients without ASP. This moderation by ASP was not found in BD or HC groups. In patients with SZ, the interaction between ICV and a history of the ASP was specifically related to the verbal subcomponent of IQ as measured by WASI.
The significant positive association between ICV and IQ in patients with SZ who had experienced ASP might indicate abnormal neurodevelopment. Our findings give support for ICV together with verbal intellectual abilities as clinically relevant markers that can be added to prediction tools to enhance evaluations of SZ risk.
Previous systematic reviews and meta-analyses of cross-sectional data assessing the effect of cannabis on cognitive functioning and intelligence show inconsistent results. We hypothesized that frequent and dependent cannabis use in youth would be associated with Intelligence Quotient (IQ) decline. This study is a systematic review and meta-analysis. We searched Embase, PubMed and PsychInfo from inception to 24 January 2020. We included studies with non-treatment seeking samples and pre- and post-exposure measures of IQ. We requested data from authors if summary data was not available from published work. We preregistered our review with PROSPERO (ID no. CRD42019125624). We found seven cohort studies including 808 cases and 5308 controls. We found a significant effect for the association between frequent or dependent cannabis use in youth and IQ change, Cohen's d = −0.132 (95% CI −0.198 to −0.066) p < 0.001. Statistical heterogeneity between studies was also low at I2 = 0.2%. Study quality was moderate to high. This translates to an average decline of approximately 2 IQ points following exposure to cannabis in youth. Future studies should have longer periods of follow up to assess the magnitude of developmental impact.
There is a common misconception that our genomes - all unique, except for those in identical twins - have the upper hand in controlling our destiny. The latest genetic discoveries, however, do not support that view. Although genetic variation does influence differences in various human behaviours to a greater or lesser degree, most of the time this does not undermine our genuine free will. Genetic determinism comes into play only in various medical conditions, notably some psychiatric syndromes. Denis Alexander here demonstrates that we are not slaves to our genes. He shows how a predisposition to behave in certain ways is influenced at a molecular level by particular genes. Yet a far greater influence on our behaviours is our world-views that lie beyond science - and that have an impact on how we think the latest genetic discoveries should, or should not, be applied. Written in an engaging style, Alexander's book offers tools for understanding and assessing the latest genetic discoveries critically.
The ‘jumping to conclusions’ (JTC) bias is associated with both psychosis and general cognition but their relationship is unclear. In this study, we set out to clarify the relationship between the JTC bias, IQ, psychosis and polygenic liability to schizophrenia and IQ.
A total of 817 first episode psychosis patients and 1294 population-based controls completed assessments of general intelligence (IQ), and JTC, and provided blood or saliva samples from which we extracted DNA and computed polygenic risk scores for IQ and schizophrenia.
The estimated proportion of the total effect of case/control differences on JTC mediated by IQ was 79%. Schizophrenia polygenic risk score was non-significantly associated with a higher number of beads drawn (B = 0.47, 95% CI −0.21 to 1.16, p = 0.17); whereas IQ PRS (B = 0.51, 95% CI 0.25–0.76, p < 0.001) significantly predicted the number of beads drawn, and was thus associated with reduced JTC bias. The JTC was more strongly associated with the higher level of psychotic-like experiences (PLEs) in controls, including after controlling for IQ (B = −1.7, 95% CI −2.8 to −0.5, p = 0.006), but did not relate to delusions in patients.
Our findings suggest that the JTC reasoning bias in psychosis might not be a specific cognitive deficit but rather a manifestation or consequence, of general cognitive impairment. Whereas, in the general population, the JTC bias is related to PLEs, independent of IQ. The work has the potential to inform interventions targeting cognitive biases in early psychosis.
Associations have been described between lower IQ and serious mental illness. Associations between common mental disorders (CMDs) and IQ have received little research. The objective of this study was to investigate the association between verbal IQ and CMD symptoms and diagnoses, and to investigate the role of potential mediating and confounding factors.
Data were analysed from a British national survey with an analysed sample of 8054 people aged 16–74 years. Associations between verbal IQ (NART) and mental symptoms/disorders (CIS-R) were analysed with covariates including education, social class, income, debt, problem drinking, life events, physical health and relationship quality.
CMD was associated with lower IQ. This association was stronger for depressive disorder/symptoms than for generalised anxiety disorder/symptoms. The most important covariates were education, social class, income and relationship quality.
The association between lower IQ and CMD is partly accounted for by adverse social/socioeconomic conditions. Stronger associations for depression than anxiety may indicate an effect of IQ on the way mental distress is communicated.
Schizophrenia patients are typically found to have low IQ both pre- and post-onset, in comparison to the general population. However, a subgroup of patients displays above average IQ pre-onset. The nature of these patients’ illness and its relationship to typical schizophrenia is not well understood. The current study sought to investigate the symptom profile of high-IQ schizophrenia patients.
We identified 29 schizophrenia patients of exceptionally high pre-morbid intelligence (mean estimated pre-morbid intelligence quotient (IQ) of 120), of whom around half also showed minimal decline (less than 10 IQ points) from their estimated pre-morbid IQ. We compared their symptom scores (SAPS, SANS, OPCRIT, MADRS, GAF, SAI-E) with a comparison group of schizophrenia patients of typical IQ using multinomial logistic regression.
The patients with very high pre-morbid IQ had significantly lower scores on negative and disorganised symptoms than typical patients (RRR = 0.019; 95% CI = 0.001, 0.675, P = 0.030), and showed better global functioning and insight (RRR = 1.082; 95% CI = 1.020, 1.148; P = 0.009). Those with a minimal post-onset IQ decline also showed higher levels of manic symptoms (RRR = 8.213; 95% CI = 1.042, 64.750, P = 0.046).
These findings provide evidence for the existence of a high-IQ variant of schizophrenia that is associated with markedly fewer negative symptoms than typical schizophrenia, and lends support to the idea of a psychosis spectrum or continuum over boundaried diagnostic categories.
To investigate demographic, clinical and neuropsychological aspects of self-harm in schizophrenia and identify which are independently predictive of and therefore the most relevant to clinical intervention.
Subjects and methods:
Eighty-seven patients with schizophrenia were interviewed regarding substance misuse, depression, hopelessness, negative/positive symptoms and illness insight. Neuropsychological assessment included premorbid IQ, continuous performance test, cognitive-motor and trait impulsivity. A prospective three-month review of medical records was also undertaken.
Fifty-nine patients (68%) reported past self-harm (including attempted suicide). Those with past self-harm, compared to those without, were significantly more likely to report depression, hopelessness, impulsivity, a family history of self-harm, polysubstance abuse and had higher premorbid IQ. Logistic regression revealed that depression, higher premorbid IQ and polysubstance abuse were independently linked to self-harm. Five participants attempted self-harm during the 3-month prospective follow-up period. These all had a history of past self-harm and were significantly more likely to have been depressed at the initial interview than those who did not go on to self-harm.
Discussion and conclusions:
Independent predictors of self-harm in schizophrenia are premorbid IQ and polysubstance abuse. In addition, depression was both independently associated with past self-harm and predictive of self-harm in the follow-up period.
How are intelligence and creativity related? Given the dynamic and complex nature of both constructs, this question is a nuanced one. This chapter first discusses how creativity is represented in intelligence theories (such as Guilford’s Structure of Intellect, CHC, and successful intelligence, and how intelligence is represented in creativity theories (such as systems and componential theories, domain-based theories, and cognitive theories). Next, empirical studies are reviewed. The threshold theory, which proposes that intelligence and creativity are related but only up to about an IQ of 120, has received mixed support. More recent studies using sophisticated statistical analyses have found more evidence. A reliance on measures of divergent thinking and g as the sole tests of creativity and intelligence may also limit much existing research.
The purpose of this chapter is to explore the extent that the claim of racial differences in intelligence represents a Black and White (i.e., absolute) issue, in a post-truth era characterized by discourses that are no longer moored in T/truth. Specifically, we summarize the debate over racial differences in intelligence. In so doing, we deconstruct the concepts of race and intelligence. Next, using Onwuegbuzie, Daniel, and Collins’s (2009) meta-validation model, we assess the fidelity of IQ tests. Then, we provide arguments that challenge hereditarian assumptions about the largely genetic nature of intelligence, including delineating evidence of the relationship between IQ and socioeconomic status (and its many correlates). We call for continued rigorously peer-reviewed research on race and intelligence, particularly with regard to the etiology of differences in IQ scores, wherein the investigators are comprehensive, transparent, and cautious, given the potential for divisiveness and far-reaching sociopolitical implications in a post-truth era.
IQ as a measure of intelligence is at the same time a success and a failure: a success because of the predictive value of IQ, and a failure because we do not know precisely what it is measuring. Intelligence has been defined in many ways. To discuss the definitional issue, we rely on Aristotle and his four ways to define something: explaining what it looks like, what it consists of, where it comes from, and what it is for. In this chapter we present an alternative view on how the measurement of intelligence has evolved and how it relates to different views on what intelligence is. The first initiatives to measure intelligence were inspired by physics and a strictly quantitative approach. These initiatives were based on the notion of general intelligence as mental energy, and led to tests to measure intelligence such as reaction times and perceptual discrimination (i.e., what intelligence looks like). IQ as a quantification of intelligence is from a later date and is based on a quite different type of test, inspired by an interest in what intelligence is for, as expressed in the work of some of the most famous intelligence test developers (e.g., Binet, Terman, Wechsler). The type of content of these tests is preserved in most intelligence tests today, mainly because of the predictive success of IQ tests. There now is also agreement that intelligence is not unitary but multidimensional. Robert Sternberg’s major endeavor to unravel processes has shown that there is no clear-cut answer to the question of what intelligence consists of in terms of cognitive processes or how processes can be measured. Other endeavors have resulted in measurement of genetic and environmental influences, in a revival of reaction time and discrimination measures, and in hypotheses about biological mechanics, such as mitochondrial efficiency. We conclude that intelligence is still a vague concept without much hope that it will be clarified soon, even though its measurement through a variety of cognitive tasks seems to work well from a predictive point of view.
The prevalence and impact of motor coordination difficulties in children with copy number variants associated with neurodevelopmental disorders (ND-CNVs) remains unknown. This study aims to advance understanding of motor coordination difficulties in children with ND-CNVs and establish relationships between intelligence quotient (IQ) and psychopathology.
169 children with an ND-CNV (67% male, median age = 8.88 years, range 6.02–14.81) and 72 closest-in-age unaffected siblings (controls; 55% male, median age = 10.41 years, s.d. = 3.04, range 5.89–14.75) were assessed with the Developmental Coordination Disorder Questionnaire, alongside psychiatric interviews and standardised assessments of IQ.
The children with ND-CNVs had poorer coordination ability (b = 28.98, p < 0.001) and 91% of children with an ND-CNV screened positive for suspected developmental coordination disorder, compared to 19% of controls (OR = 42.53, p < 0.001). There was no difference in coordination ability between ND-CNV genotypes (F = 1.47, p = 0.184). Poorer coordination in children with ND-CNV was associated with more attention deficit hyperactivity disorder (ADHD) (β = −0.18, p = 0.021) and autism spectrum disorder trait (β = −0.46, p < 0.001) symptoms, along with lower full-scale (ß = 0.21, p = 0.011), performance (β = −0.20, p = 0.015) and verbal IQ (β = 0.17, p = 0.036). Mediation analysis indicated that coordination ability was a full mediator of anxiety symptoms (69% mediated, p = 0.012), and a partial mediator of ADHD (51%, p = 0.001) and autism spectrum disorder trait symptoms (66%, p < 0.001) as well as full scale IQ (40%, p = 0.002), performance IQ (40%, p = 0.005) and verbal IQ (38%, p = 0.006) scores.
The findings indicate that poor motor coordination is highly prevalent and closely linked to risk of mental health disorder and lower intellectual function in children with ND-CNVs. Future research should explore whether early interventions for poor coordination ability could ameliorate neurodevelopmental risk.
Lifespan outcomes of simultaneous versus sequential myelomeningocele repair and shunt placement or effects of repeated shunt revisions on specific domains of IQ or fine motor dexterity are largely unknown. The current study addressed these gaps in a large cohort of children and adults with spina bifida myelomeningocele (SBM).
Participants between 7 and 44 years of age with SBM and shunted hydrocephalus were recruited from international clinics at two time points. Each participant completed a standardized neuropsychological evaluation that included estimates of IQ and fine motor dexterity. Simultaneous versus sequential surgical repair and number of shunt revisions were examined in relation to long-term IQ and fine motor scores.
Simultaneous myelomeningocele repair and shunting were associated with more frequent shunt revisions, as well as to lower Full Scale and verbal IQ scores, controlling for number of shunt revisions. More shunt revisions across study time points were associated with higher nonverbal IQ (NVIQ) scores. No effects were observed on fine motor dexterity.
Findings indicate generally greater influence of surgery type over shunt revision history on outcomes in well-managed hydrocephalus. Findings supported apparent, domain-specific benefits of sequential compared to simultaneous surgery across the lifespan in SBM. Higher NVIQ scores with greater number of additional shunt revisions across surgery type supported positive outcomes with effective surgical management for hydrocephalus.
Attention-deficit hyperactivity disorder (ADHD) is associated with poorer cognitive functioning. We used a developmental, genetically-sensitive approach to examine intelligence quotient (IQ) from early childhood to young adulthood among those with different ADHD courses to investigate whether changes in ADHD were reflected in differences in IQ. We also examined executive functioning in childhood and young adulthood among different ADHD courses.
Study participants were part of the Environmental Risk (E-Risk) Longitudinal Twin Study, a population-based birth cohort of 2232 twins. We assessed ADHD in childhood (ages 5, 7, 10 and 12) and young adulthood (age 18). We examined ADHD course as reflected by remission, persistence and late-onset. IQ was evaluated at ages 5, 12 and 18, and executive functioning at ages 5 and 18.
ADHD groups showed deficits in IQ across development compared to controls; those with persistent ADHD showed the greatest deficit, followed by remitted and late-onset. ADHD groups did not differ from controls in developmental trajectory of IQ, suggesting changes in ADHD were not reflected in IQ. All ADHD groups performed more poorly on executive functioning tasks at ages 5 and 18; persisters and remitters differed only on an inhibitory control task at age 18.
Differences in ADHD course – persistence, remission and late-onset – were not directly reflected in changes in IQ. Instead, having ADHD at any point across development was associated with lower average IQ and poorer executive functioning. Our finding that individuals with persistent ADHD have poorer response inhibition than those who remitted requires replication.
To improve global human capital, an understanding of the interplay of endowment across the full range of socioeconomic status (SES) is needed. Relevant data, however, are absent in the nations with the most abject poverty (Tucker-Drob & Bates, 2016), where the lowest heritability and strong effects of SES are predicted. Here we report the first study of biopsychosocial gene–environment interaction in extreme poverty. In a sub-Saharan sample of early teenage twins (N = 3192), we observed substantial (~30–40%) genetic influence on cognitive abilities. Surprisingly, shared environmental influences were similar to those found in adolescents growing in Western affluent countries (25–28%). G × SES moderation was estimated at aˋ = .06 (p = .355). Family chaos did not moderate genetic effects but did moderate shared environment influence. Heritability of cognitive abilities in extreme poverty appears comparable to Western data. Reduced family chaos may be a modifiable factor promoting cognitive development.
Mood disturbance is frequent after traumatic brain injury (TBI), often assessed using the Hospital Anxiety and Depression Scale (HADS). Research supports a three-factor HADS structure (anxiety, depression, and psychomotor), although this has not been used to investigate demographic variables and mood outcome post-TBI. This study examined severity of TBI, demographic variables [age, gender, estimated premorbid IQ (EIQ), relationship status, employment status, socio-economic status (SES)], and mood outcome, using HADS factor scores from a large adult population sample in Tasmania.
HADS factor scores were calculated for an initial sample of 596 adults. The sample sizes varied according to those attending at 1, 6, 12 and 24 months post-TBI and the available data for each dependent variable.
Significantly higher anxiety, depression, and psychomotor scores were reported at most follow-ups by females, the middle-aged, and those with lower IQs. Longer post-traumatic amnesia (PTA) was associated with significantly greater mood problems. Occasional significant findings at earlier follow-ups for the factors were noted for those unemployed. Other variables were rarely significant. PTA, premorbid IQ, and Age were included in most Multiple Regression equations predicting outcome for the factors, with Gender included for Anxiety and depression at 6 months after injury.
Key demographic variables and PTA severity relate to mood post-TBI, and contribute to predicting mood outcome. Differences in findings for the three factors support their use in clinical practice.
A test of Jensen effects is of nil value as a diagnostic instrument when various good-sized meta-analyses show Jensen effects appear for both genetic effects and environmental effects. Using thought experiments, Flynn (2019) claims that some schooling gains yield Jensen effects, which should not be the case for an environmental effect. However, a meta-analysis (K = 12, total N = 60,993, mean r = 0.13) of schooling gains shows no Jensen effect. Real data trump thought experiments, so it is concluded there is no empirical proof of anomalous Jensen effects for schooling gains.
Spearman’s hypothesis tested at the subtest level of an IQ battery states that differences between races on the subtests of an IQ battery are a function of the g loadings of these subtests, such that there are small differences between races on subtests with low g loadings and large differences between races on subtests with high g loadings. Jensen (1998) stated that Spearman’s hypothesis is a law-like phenomenon. It has also been confirmed many times at the level of items of the Raven’s Progressive Matrices. This study hypothesizes that with concern to Spearman’s hypothesis, subtests and items function in fundamentally the same way, and tested whether Spearman’s hypothesis is confirmed at the item level for White–East Asian comparisons. A group of Korean young adults (N=205) was compared with other groups of young adults from Canada, the US, Russia, Peru and South Africa (total N=4770) who took the Advanced Progressive Matrices. Spearman’s hypothesis was strongly confirmed with a sample-size-weighted r with a value of 0.63. Computing the g loadings of the items of the Raven with either the Raven-g or the Wechsler-g led to the same conclusions. Tests of Spearman’s hypothesis yielded less-strong outcomes when the 36-item Advanced Progressive Matrices were used than when the 60-item Standard Progressive Matrices were used. There is a substantial correlation between sample size and the outcome of Spearman’s hypothesis. So, all four hypotheses were confirmed, showing that a part of the subtest-level nomological net replicates at the item level, strengthening the position that, with concern to Spearman’s hypothesis, subtests and items function fundamentally the same. It is concluded that Spearman’s hypothesis is still a law-like phenomenon. Detailed suggestions for follow-up research are made.