Unitary or non-unitary nature of working memory? Evidence from its relation to general fluid and crystallized intelligence

Low level lead exposure in early childhood and parental education on adolescent IQ and working memory: a cohort study

BACKGROUND

The independent effect of lead exposure and parental education on children's neurocognition is well-documented. However, few studies have examined the combined effect of childhood lead exposure and parental education on adolescent neurocognition, especially in China.

OBJECTIVE

Examine both the combined and interactive effect of childhood blood lead levels (BLLs) and parental education on early adolescent neurocognition.

METHODS

417 children from a longitudinal cohort study in Jintan, China had BLLs measured at 3-5 years and 12 years, parental education levels assessed at 3-5 years, and neurocognitive outcomes tested at 12 years.

RESULTS

BLLs at 3-5 years were inversely associated with adolescent IQ (β -0.55 95% CI: -0.97, -0.13) but not working memory (β -0.06 95% CI: -0.23, 0.11) and parental education was positively associated with adolescent IQ (β 0.68 95% CI: 0.19, 1.17) and working memory (β 0.24 95% CI: 0.04, 0.44). BLLs and parental education evidenced combined effects on neurocognition, where children with higher BLLs and lower fathers' education had mean IQ scores 7.84 (95% CI: -13.15, -2.53) points lower than children with lower BLLs and higher fathers' education. There were significant associations between parental education and working memory, however, not with BLLs. The interaction between mother and father high school education and BLLs was insignificant for effects on IQ and working memory.

SIGNIFICANCE

Childhood lead exposure and parental education levels have a combined and long-term impact on IQ, evidence that may partially explain disparities in lead exposure associated outcomes and highlight those children at greatest risk for neurocognitive deficits.

IMPACT STATEMENT

Children continue to be exposed to low-levels of environmental lead in China and globally, warranting examination of the impact of such exposures. This paper demonstrates that even relatively low-level lead exposure in early childhood significantly influences adolescent neurocognitive functioning. Furthermore, co-existing social determinant of health-related variables, measured here as parental education, have a combined impact on neurocognition. These results highlight children at greater risk for neurocognitive deficits and demonstrate the need to examine the influence of lead exposure within the broader socio- ecological environment, as these factors work in tandem to influence longer-term neurocognitive outcomes.

Childhood lead exposure and sex-based neurobehavioral functioning in adolescence

It is well documented that childhood lead exposure is associated with long-term decreases in intelligence quotients (IQ). Lesser known is the relationship with neurobehavioral domains, especially in adolescence. This study sought to identify cross-sectional and longitudinal associations between lead exposure and adolescent executive and visual-motor functioning and examine sex-based differences. Participants were 681 children from Jintan, China who had their blood lead levels (BLLs) assessed at age 3-5 years and 12 years old and neurobehavioral functioning assessed through the University of Pennsylvania Computerized Neurocognitive Battery (PennCNB) platform http://www.med.upenn.edu/bbl at 12 years old. Mean BLLs were 6.41 mcg/dl at age 3-5 years and 3.10 mcg/dl at 12. BLLs at 3-5 years and 12 years were used as predictors for the individual neurobehavioral domains in general linear models while controlling for father and mother occupation and education, residence location, age, and adolescent IQ. Models were run separately for males and females. In adjusted models, males BLLs at 3-5 years were associated with increased time to correctly complete tasks in multiple domains including abstraction/flexibility (β = 19.90, 95% CI( 4.26, 35.54) and spatial processing (β = 96.00, 95% CI 6.18, 185.82) at 12 years. For females in adjusted models, BLLs at 3-5 years were associated with increasing time to correctly complete tasks on the episodic memory domain task (β = 34.59, 95% CI 5.33, 63.84) at 12 years. Two adolescent cross-sectional relationships remained in the adjusted models for males only, suggesting a positive association between BLLs and increasing time for correct responses on the attentional domain task (β = 15.08, 95% CI 0.65, 29.51) and decreasing time for correct responses on the episodic memory task (β = -73.49, 95% CI -138.91, -8.06) in males at 12 years. These associations remained with and without controlling for IQ. These results suggest that lead exposure is associated with overall deficits in male and female neurobehavioral functioning, though in different domains and different timing of exposure.

Assessment of cross-cultural measurement invariance of the NIH toolbox fluid cognition measures between Jamaicans and African-Americans

The NIH Toolbox Cognitive Battery (NIHTB-CB) was developed as a common-metric, computerized cognitive screener for research. Although extensively normed and validated in Americans of different ethnicities, there is little data on how generalizable such results would be when used outside of the United States. The objective of this study was to assess measurement invariance (MI) of the NIHTB-CB across Jamaican and African-American samples and determine appropriateness of comparisons across groups. Multi-group confirmatory factor analyses using a single-factor model were conducted using five tests of fluid cognitive abilities from the NIHTB-CB, which assess working memory, episodic memory, processing speed, and executive function. MI was tested sequentially for configural, metric and scalar invariance. 125 Jamaican and 154 American adults of African descent were included. The Jamaican mean age was 31.6 ± 8.6 years (57% males) compared to 43.5 ± 15.5 years (25% males) for the African-American group. The Jamaicans had on average 11.3 ± 2.7 years of education compared to 13.9 ± 2.6 years for the African-Americans. We found metric and configural invariance across both samples but not scalar invariance. These findings suggest that the single factor emerging from the NIHTB-CB measures the same construct, i.e. fluid cognitive ability, in both groups and hence the battery is appropriate for assessments within cultures. However, lack of scalar invariance indicates that direct cross-cultural comparisons of performance levels should be interpreted with caution, also suggesting that U.S. normative standards are not generalizable to the Jamaican population.

The domain-specificity of serial order working memory

Making a turn while driving is simple: turn on the indicator, check for cars, then turn. Two types of information are required to perform this sequence of events: information about the items (e.g., the correct indicator), and the serial order of those items (e.g., checking before turning rather than vice-versa). Previous research has found distinct working memory capacities (WMCs) for item and serial order information in both verbal and nonverbal domains. The current study investigates whether the serial order WMC is shared for sequences from different content domains. One hundred and fifty-three participants performed sequence matching tasks with verbal (letters and words) and nonverbal (locations and arrows) stimuli. The accuracy of detecting mismatched item-identity and serial order information in sequences was used to operationalize item and order WMC. Using structural equation modeling analyses, we directly compared models that included either domain-specific or domain-general serial order WMC latent variables, finding that models with domain-specific serial order WMC latent variables for verbal and nonverbal materials fit the data better than models with domain-general latent variables. The findings support the hypothesis that there are separate capacities for serial order working memory depending on the type of material being ordered.

Changing relations among cognitive abilities across development: implications for measurement and research

OBJECTIVE

The constructs of intelligence and executive function (EF) are commonly used in neuropsychological, cognitive, and developmental research, and in the context of clinical assessment. Yet, we have a limited understanding of the changing age-related associations among these cognitive constructs and the implications for measurement and research. The objectives of this study were to compare hypothetical models using intellectual abilities (non-age corrected scores of intelligence or IQ) and experimental measures of EF and to better understand the role of age in determining the associations between these cognitive abilities at two different periods of development. We also incorporated prediction of ADHD-related difficulties.

METHOD

We examined intellectual abilities and EF in a typically developing child sample (N = 250) and young-adult sample (N = 329). We used confirmatory factor analysis to estimate models for each developmental period: a one-factor model of general cognitive ability and a two-factor model of intelligence and EF. ADHD-related difficulties were regressed on the factors from each model.

RESULTS

Age was more strongly related to all cognitive abilities in the child sample than in the young-adult sample. In the factor analytic models, higher amounts of cognitive test score variance were explained by both models in the child sample than in the young-adult sample. Further, in the child sample, the general cognitive ability factor (combining intellectual abilities and EF) was a significant predictor of ADHD-related difficulties, but the separate intellectual ability and EF factors were not.

CONCLUSIONS

Variables highly associated with age (such as intellectual ability and EF) should not be statistically controlled when assessing cognitive constructs especially in child samples when there is rapid change in cognitive abilities.

Association between Serum Copper Status and Working Memory in Schoolchildren

Trace elements such as copper are essential micronutrients. Traditionally, copper has been studied in the context of micronutrient deficiencies. Recent studies in both animals and humans, however, have revealed that elevated blood copper can also have adverse effects on cognitive function since free copper can cross the blood-brain barrier and subsequently impose oxidative stress to neuronal cells. However, most of these human studies were conducted in adult populations with and without cognitive decline, and there are few studies on the effect of excess copper on cognitive function in children. This project seeks to look at the effects of elevated copper levels on cognitive development in a population of school age children (ages 10–14 years with mean age of 12.03 years and standard deviation (SD) of 0.44) from Jintan, China. Briefly, serum copper levels and working memory test scores were collected from a sample of 826 children with a mean serum copper level of 98.10 (SD 0.75). Copper level was considered as a categorical variable (taking the first group as those with as ≤84.3 μg/dL, the second group as >84.3 and ≤110.4 μg/dL, and the third group as >110.4 μg/dL with the cut-off values defined by the first and third quartiles of the sample). Results showed a significant association between high copper levels (>110.4 μg/dL) and poorer working memory in boys but this association was not seen in lower copper levels in either sex. These results suggests that in school age children, like in adults, elevated copper levels have the potential to adversely affect cognition.