Influence of HIV infection on cognition and overall intelligence in HIV-infected individuals: advances and perspectives

It is now well understood that HIV-positive individuals, even those under effective ART, tend to develop a spectrum of cognitive, motor, and/or mood conditions which are contemporarily referred to as HIV-associated neurocognitive disorder (HAND), and which is directly related to HIV-1 infection and HIV-1 replication in the central nervous system (CNS). As HAND is known to induce difficulties associated with attention, concentration, and memory, it is thus legitimate and pertinent to speculate upon the possibility that HIV infection may well influence human cognition and intelligence. We therefore propose herein to review the concept of intelligence, the concept of cells of intelligence, the influence of HIV on these particular cells, and the evidence pointing to differences in observed intelligence quotient (IQ) scores between HIV-positive and HIV-negative individuals. Additionally, cumulative research evidence continues to draw attention to the influence of the gut on human intelligence. Up to now, although it is known that HIV infection profoundly alters both the composition and diversity of the gut microbiota and the structural integrity of the gut, the influence of the gut on intelligence in the context of HIV infection remains poorly described. As such, we also provide herein a review of the different ways in which HIV may influence human intelligence via the gut-brain axis. Finally, we provide a discourse on perspectives related to HIV and human intelligence which may assist in generating more robust evidence with respect to this issue in future studies. Our aim is to provide insightful knowledge for the identification of novel areas of investigation, in order to reveal and explain some of the enigmas related to HIV infection.

Intelligence Correlates with the Temporal Variability of Brain Networks

Intelligence is the ability to recognize and understand objective things, and use knowledge and experience to solve problems. Highly intelligent people show the ability to switch between different thought patterns and shift their mental focus. This suggests a link between intelligence and the dynamic interaction of brain networks. Thus, we investigated the relationships between resting-state dynamic brain network remodeling (temporal variability) and scores on the Wechsler Adult Intelligent Scale using a large dataset comprising 606 individuals. We found that performance intelligence was associated with greater temporal variability in the functional connectivity patterns of the dorsal attention network. High variability in these areas indicates flexible connectivity patterns, which may contribute to cognitive processes such as attention selection. In addition, performance intelligence was related to greater temporal variability in the functional connectivity patterns of the salience network. Thus, this study revealed a close relationship between performance intelligence and high variability in brain networks involved in attentional choice, spatial orientation, and cognitive control.

Predictors of Cognitive Function in Community-Dwelling Older Adults by Age Group: Based on the 2017 National Survey of Older Korean Adults

Owing to a growing older adult population, dementia is emerging as an important health issue. Given that maintaining cognitive functions is crucial for the prevention of dementia, this study aimed to identify the predictors of cognitive function in community-dwelling older adults, through a secondary data analysis of the 2017 National Survey of Older Koreans. A total of 9836 participants were classified into three age groups—young-old (65–74 years), old-old (75–84 years), and oldest-old (≥85 years)—and were separately analyzed using multiple linear regression models. The final model explained 28.0%, 35.0%, and 37.0% of variance in cognitive function in the three age groups, respectively. The most potent predictors of cognitive function in the young-old were electronic device-based activities, instrumental activities of daily living (IADL), and nutrition management; the predictors for the old-old group were electronic device-based activities, IADL, and dementia screening, and those for the oldest-old group were frequency of contact with acquaintances, traveling, and religion. Thus, age group-specific interventions are needed to effectively promote cognitive function among older adults. Digital literacy education, use of community-based elderly welfare programs, opportunities for social interactions, and physical activities can help older adults in maintaining a functional status and muscle strengthening.

Socioeconomic Position and Late-Onset Dementia: A Nationwide Register-Based Study

OBJECTIVES

Previous research on the association between socioeconomic position (SEP) and dementia has not sufficiently accounted for the complex relationship between education and occupation. We investigated the independent and joint effects of educational attainment and occupation-based SEP on dementia.

METHODS

We used register-based information about educational attainment, occupation-based SEP, and dementia from 1,210,720 individuals. Information about cognitive ability at conscription was available for a subsample of men.

RESULTS

When mutually adjusted, lower educational attainment and occupation-based SEP were associated with higher dementia risk in a dose-response manner. Higher occupation-based SEP partly mitigated the higher dementia risk associated with lower educational attainment. After adjusting for cognitive ability in a subgroup of men, only unskilled work was associated with higher dementia risk.

DISCUSSION

Occupation-based SEP is independently associated with dementia and may mitigate the higher dementia risk associated with short education. Future research should elucidate the mechanisms underlying social inequality in dementia.

Influence of childhood socioeconomic position and ability on mid-life cognitive function: evidence from three British birth cohorts

BACKGROUND

Childhood socioeconomic position (SEP) is robustly associated with cognitive function later in life. However, it is unclear whether this reflects a direct relationship, or an indirect association via modifiable factors such as educational attainment and occupation. We sought to clarify these associations using retrospectively harmonised data from three ongoing British birth cohorts.

METHODS

We analysed data from the 1946 National Survey of Health and Development (n=2283), the 1958 National Child Development Study (n=9385) and the 1970 British Cohort Study (n=7631). Retrospective harmonisation was used to derive equivalent indicators of cognition, SEP, education and occupation across the three cohorts. Structural equation modelling was used to examine the association between childhood SEP and mid-life cognitive function, via childhood cognitive ability, educational attainment and mid-life occupation.

RESULTS

Across all three cohorts, no direct pathways were observed between childhood SEP and mid-life cognitive function. Rather, this association was indirect via the three temporally ordered mediators. In addition, the direct pathway between childhood cognition and adult cognitive function was weaker in the two younger studies.

CONCLUSIONS

Across three British birth cohorts, we found that the association between early life SEP and mid-life cognitive function was fully mediated by childhood cognitive ability, educational attainment and occupational status. Furthermore, the association between early cognitive ability and mid-life cognitive function has decreased in younger generations. Therefore, cognitive function in adulthood may be influenced by modifiable factors and societal change.

Partnership and Cognitive Aging in Europe: Mediating Factors and Social Stratification

Objectives

Living in a partnership has been shown to benefit later life health in general and decrease the risk of cognitive impairment. Few studies have, however, examined whether different types of partnership transitions also differ with respect to their impact on cognitive trajectories, and whether financial resources, healthy behaviors, cognitive stimulation, and social integration can explain these differences.

Methods

Data came from six waves of the Survey of Health, Ageing and Retirement in Europe, which is a representative panel for the population aged 50 years or older, and were collected between 2004 and 2017 in 20 European countries. Our sample includes 215,989 valid person-year observations from 78,984 persons. The mean age at baseline is 64 years, and individuals were observed on average 2.7 times. Cognitive functioning was assessed with measures of immediate and delayed recall on a memory test and verbal fluency. Fixed effects regression models were employed to exploit individual-level variation in partnership and simultaneous cognitive changes.

Results

Partnership status was stable in most respondents (around 90%). Compared to remaining partnered and after controlling for sociodemographic factors, transition to divorce was associated with a steeper decline in immediate and delayed recall. Exploring possible mechanisms, both financial resources and social integration, explained these differences. Additional analyses suggested that effects were mostly driven by individuals with lower education.

Discussion

Partnership transitions remain infrequent events in later life, but our findings indicate that they can induce less favorable cognitive trajectories compared to partnered individuals, particularly for those with lower cognitive reserve.

Lifecourse socioeconomic changes and late-life cognition in a cohort of U.S.-born and U.S. immigrants: findings from the KHANDLE study

BACKGROUND

Low socioeconomic status (SES) in early and late life has been associated with lower late-life cognition. Less is known about how changes in SES from childhood to late life are associated with late-life cognition, especially among diverse populations of older adults.

METHODS

In a multi-ethnic sample (n = 1353) of older adults, we used linear regression to test associations of change in comprehensive measures of SES (financial, cultural, and social domains) from childhood to late life with semantic memory, episodic memory, and executive function. We tested whether the association between SES trajectory and late-life cognition differed by populations who resided in the U.S. during childhood or immigrated to the U.S. as adults.

RESULTS

Participants with low childhood/high late-life financial capital had better semantic memory (β = 0.18; 95% CI: 0.04, 0.32) versus those with low financial capital in both childhood and late life, regardless of childhood residence. We observed a significant interaction in the association of verbal episodic memory and cultural capital by childhood residence (p = 0.08). Participants with a foreign childhood residence had higher verbal episodic memory if they had low childhood/high late-life cultural capital (β = 0.32; 95% CI: 0.01, 0.63), but lower verbal episodic memory if they had high childhood/low late-life cultural capital (β = - 0.40; 95% CI: - 0.94, 0.13). Having high lifecourse social capital was associated with better verbal episodic memory scores among those with a U.S. childhood (β = 0.34; 95% CI: 0.14, 0.55), but lower verbal episodic memory among those with a foreign childhood (β = - 0.10; 95% CI: - 0.51, 0.31).

CONCLUSIONS

High financial and cultural capital in late life is associated with better cognition, regardless of early childhood SES or childhood residence.

Association between socioeconomic status and cognitive functioning among older adults in Ghana

OBJECTIVES

Extensive analysis of the associations between socioeconomic status and cognition has been conducted among older adults. However, it is not clear whether associations in high-income countries are similar in low-and middle-income countries. This research aims to investigate the association between the socioeconomic status of older adults in Ghana and their cognitive function by using a sample of older adults that is nationally representative.

METHODS

Data were obtained from a sample of older Ghanaian adults (50+) from the Study of Global AGEing and Adult Health Wave 1 (n = 3710) of the World Health Organization. Objectively, cognition was measured by verbal recall, verbal fluency, forward digit span, and backward digit span, while variations in cognition overall were evaluated against socioeconomic factors using linear regression.

RESULTS

Older age, older women, rural life, increasing memory difficulty, and being diagnosed with stroke were the most significant determinants of impaired cognitive function. Higher education and higher income were significantly associated with a better cognitive function than those with no formal education and low income.

CONCLUSIONS

These results provide new evidence for public health programs in Ghana and other low-and middle-income countries to tackle cognitive impairments in growing populations.

Communications in the time of a pandemic: the readability of documents for public consumption

OBJECTIVE

Government communications in a crisis can influence public health outcomes. This research aimed to investigate if written communications of the most commonly sought sources of COVID-19 information available on the internet have readability levels commensurate with those of the general public.

METHODS

Online documents from the World Health Organization (WHO), and the governments of Australia, the UK and the US were assessed for readability using an online instrument that calculated scores for the Flesch Reading Ease Score, the SMOG Index and the Readability Consensus Grade Level.

RESULTS

Similar to the previous research, most documents assessed had a readability standard that was at or above the recommended grade level, and as such inaccessible to substantial portions of the general public. A one-way ANOVA with post hoc tests revealed significant differences among the data, with Australian documents significantly more difficult to read than those from the UK and US.

CONCLUSIONS

Government departments need to consider their audience and monitor readability of the documents they produce to ensure that readers can understand them. Implications for public health: Health communications need to be written at a level appropriate for the targeted population in order to be fit for purpose.

Childhood Socioeconomic Status and Cognitive Function Later in Life: Evidence From a National Survey in Indonesia

INTRODUCTION

Social and economic conditions in childhood have been found to predict cognitive ability in midlife and old age in high-income countries. This study examines the long-term effect of childhood conditions on cognition among a nationally representative sample of older adults in a low- and middle-income country.

MATERIALS AND METHODS

Data were obtained from the 2014 to 2015 Indonesia Family Life Survey Wave 5 (6676 respondents, aged 50 years and older). Cognitive function was assessed based on total score on a series of tests adapted from the Telephone Interview for Cognitive Status. Retrospective information was collected on childhood poverty, with questions including whether respondents ever experienced hunger before age 15, whether basic facilities were available, and the number of books in the childhood home. We used linear regression to examine the association between childhood conditions and cognitive function in later life.

RESULTS

The findings show that the numbers of facilities and books available in childhood homes are substantially associated with cognition in later life after taking adulthood characteristics into account. Childhood hunger has no significant association with cognitive ability in later life. Belonging to an older birth cohort and living in a rural area were shown to have negative associations with cognitive ability in Indonesia.

CONCLUSIONS

Our findings suggest that childhood poverty, birth cohort, and living in a rural area may contribute to cognitive aging in Indonesia. Policies and interventions that target childhood poverty in developing countries may also recognize the rural-urban divide in access to educational and other socioeconomic resources.

College Selectivity and Later-Life Memory Function: Evidence From the Wisconsin Longitudinal Study

Research has shown a consistent association between college completion and laterlife cognition. We extend this work by examining whether college selectivity—the achievement level required to gain admission to a college—is associated with memory functioning more than 50 years later. We analyze data from 10,317 participants in the 1957–2011 Wisconsin Longitudinal Study to examine the relationship between college selectivity and later-life memory. Models control for childhood, midlife socioeconomic status, and later-life health and adjust for selection bias. Selective college attendance was associated with small benefits in memory at age of 72 even after accounting for socioeconomic status in both childhood and midlife and later-life health. The results of this study suggest that college selectivity may be an important component of the education–cognitive functioning relationship that has modest implications for intracohort differences in later-life cognition.

Early-life socioeconomic status, adolescent cognitive ability, and cognition in late midlife: Evidence from the Wisconsin Longitudinal Study

Although the association between childhood socioeconomic status (SES) and late-life cognition is well-established, the mechanisms underlying this association are less clear. One important potential mediator seldom examined is adolescent cognitive ability. To address this gap, we examined 5,880 respondents from the Wisconsin Longitudinal Study, which follows a random sample of high school students who graduated from Wisconsin high schools in 1957. Structural equation models were used to examine the direct and indirect effects of childhood SES on cognition in late midlife through adolescent cognitive ability, educational attainment, midlife economic condition, and midlife health. Cognitive function was measured as a latent variable composed of scores from 6 cognitive assessments including immediate and delayed recall, digit ordering, letter and category fluency, and a subset of the Wechsler Adult Intelligence Scale similarities test. We found that childhood SES predicts cognition in late midlife, and this association is largely mediated by adolescent cognitive ability and educational attainment and to a lesser extent by midlife economic condition and health. The findings underscore the long-arm of childhood SES in cognitive function in later life and highlight the complex life-course pathways underlying the association between childhood SES and cognition.

Association between childhood socioeconomic status and subjective memory complaints among older adults: results from the Japan Gerontological Evaluation Study 2010

BACKGROUND

Subjective memory complaints (SMC) have been suggested as an early marker of mild cognitive impairment and dementia. However, there is a paucity of evidence on the effects of early life conditions on the development of SMC in old age. This study is aimed at investigating the association between childhood socioeconomic status (SES) and SMC in community-dwelling older adults.

METHODS

We used the data of the Japan Gerontological Evaluation Study, a population-based cohort study of people aged 65 years or older enrolled from 28 municipalities across Japan. Childhood SES and SMC in everyday life were assessed from the self-report questionnaire administered in 2010 (n = 16,184). Poisson regression was performed to determine their association, adjusted for potential confounders and life-course mediators and examined cohort effects.

RESULTS

We identified SMC in 47.4% of the participants. After adjusting for sex, age, and number of siblings, low and middle childhood SES were associated with 29% (prevalence ratio [PR]: 1.29, 95% confidence interval [CI]: 1.22, 1.36) and 10% higher prevalence of SMC (PR: 1.10, 95%CI: 1.04, 1.17), respectively, compared with high childhood SES (p for trend <.001). The interaction terms between childhood SES and age groups were not statistically significant.

CONCLUSION

Childhood SES is significantly associated with SMC among community-dwelling older adults. Efforts to minimize childhood poverty may diminish or delay the onset of SMC and dementia in later life.

Lifecourse epidemiology matures: Commentary on Zhang et al. "Early-life socioeconomic status, adolescent cognitive ability, and cognition in late midlife"

The effect of education on late life cognition has attracted substantial attention in lifecourse epidemiology, in part because of its relevance for understanding the effect of education on dementia. Although numerous studies document an association between education and later life cognition, these studies are potentially confounded by early life socioeconomic position and cognition. Good measures of these early life constructs are rarely available in data sets assessing cognition in late life. A further body of evidence has taken advantage of compulsory schooling law (CSL) instrumental variables (IV), although these estimates have been criticized based on questions about the validity of CSL IVs. In this issue of the Journal, Zhang et al. took advantage of the Wisconsin Longitudinal Study to control for both prospectively measured adolescent IQ and early life socioeconomic status in an analysis evaluating the effect of education on cognitive scores in late middle age (Zhang et al., 2019; IN THIS ISSUE). Their results indicate a moderate effect of each additional year of education on later life cognition, of approximately 0.1-0.15 standard deviations per year of schooling. These estimates are remarkably aligned with findings from prior observational designs and from the CSL IV studies. Although criticisms of any individual study are plausible, this new study complements the body of prior evidence to provide compelling evidence for the benefits of education on late life cognition.

Navigating the landscape of non-health administrative data in Scotland: A researcher's narrative

Background: There is growing interest in using routinely collected administrative data for research purposes. Following the success of research using routinely collected healthcare data, attention has turned to leveraging routinely-collected non-health data derived from systems providing other services to the population (e.g., education, social security) to conduct research on important social problems. In Scotland, specialised organisations have been set up to support researchers in their pursuit of using and linking administrative data. The landscape of administrative data in Scotland, however, is complex and changeable, and is often difficult for researchers to navigate.

Purpose: This paper provides a researcher’s narrative of the steps required to gain the various approvals necessary to access and link non-health administrative data for research in social and cognitive epidemiology.

Findings: This paper highlights the problems, particularly regarding the length and complexity of the process, which researchers typically face, and which result in a challenging research environment. The causes of these problems are discussed, as are potential solutions.

Conclusions: Whereas the potential of non-health administrative data is great, more work and investment are needed on the part of all those concerned – from researchers to data controllers – in order to realise this potential.

Genes, Cells and Brain Areas of Intelligence

What is the neurobiological basis of human intelligence? The brains of some people seem to be more efficient than those of others. Understanding the biological foundations of these differences is of great interest to basic and applied neuroscience. Somehow, the secret must lie in the cells in our brain with which we think. However, at present, research into the neurobiology of intelligence is divided between two main strategies: brain imaging studies investigate macroscopic brain structure and function to identify brain areas involved in intelligence, while genetic associations studies aim to pinpoint genes and genetic loci associated with intelligence. Nothing is known about how properties of brain cells relate to intelligence. The emergence of transcriptomics and cellular neuroscience of intelligence might, however, provide a third strategy and bridge the gap between identified genes for intelligence and brain function and structure. Here, we discuss the latest developments in the search for the biological basis of intelligence. In particular, the recent availability of very large cohorts with hundreds of thousands of individuals have propelled exciting developments in the genetics of intelligence. Furthermore, we discuss the first studies that show that specific populations of brain cells associate with intelligence. Finally, we highlight how specific genes that have been identified generate cellular properties associated with intelligence and may ultimately explain structure and function of the brain areas involved. Thereby, the road is paved for a cellular understanding of intelligence, which will provide a conceptual scaffold for understanding how the constellation of identified genes benefit cellular functions that support intelligence.

Large and fast human pyramidal neurons associate with intelligence

It is generally assumed that human intelligence relies on efficient processing by neurons in our brain. Although grey matter thickness and activity of temporal and frontal cortical areas correlate with IQ scores, no direct evidence exists that links structural and physiological properties of neurons to human intelligence. Here, we find that high IQ scores and large temporal cortical thickness associate with larger, more complex dendrites of human pyramidal neurons. We show in silico that larger dendritic trees enable pyramidal neurons to track activity of synaptic inputs with higher temporal precision, due to fast action potential kinetics. Indeed, we find that human pyramidal neurons of individuals with higher IQ scores sustain fast action potential kinetics during repeated firing. These findings provide the first evidence that human intelligence is associated with neuronal complexity, action potential kinetics and efficient information transfer from inputs to output within cortical neurons.

Our brains are made up of almost 100 billion brain cells. Each of them acts like a small chip: they collect, process and pass on information in the form of electrical signals. In brain areas that integrate different types of information, such as frontal and temporal lobes, brain cells have larger dendrites – long projections specialized to collect signals. Theoretical studies predict that larger dendrites help cells to initiate electrical signals faster.

Because of difficulty in accessing human neurons, it has been unknown whether any of these features also relate to human intelligence. Previous studies have revealed that people with a higher IQ have a thicker outer layer (the cortex) in areas such as the frontal and temporal lobes. But does a thicker cortex also contain cells with larger dendrites and is their role different?

To test whether smarter brains are equipped with faster and larger cells, Goriounova et al. studied 46 people who needed surgery for brain tumors or epilepsy. Each took an IQ test before the operation. To access the diseased tissue deep in the brain, the surgeon also removed small, undamaged samples of temporal lobe. These samples still contained living cells and their electrical signals were measured in the lab. The experiments showed that cells from people with a higher IQ had larger dendrites that transported information more quickly, especially when they are very active. Computer models were then used to understand how these findings can lead to more efficient information transfer in human neurons.

Traditionally, research on human intelligence has focused on three main strategies: to study brain structure and function, to find genes associated with intelligence and to study the connection between our mind and behavior. Goriounova et al. are the first to take the single-cell perspective and link cell properties to human intelligence. The findings could help connect these separate approaches, and explain how genes for intelligence lead to thicker cortices and faster reaction times in people with higher IQ.

Education and Cognitive Aging: Accounting for Selection and Confounding in Linkage of Data From the Danish Registry and Survey of Health, Ageing and Retirement in Europe

Earlier studies report inconsistent associations between education and cognitive aging. We assessed the association, accounting for selective dropout due to death or dementia, and, in a subsample, accounting for confounding by early-life intelligence. Data from the Danish component of the Survey of Health, Ageing and Retirement in Europe (n = 3,400) were linked to registry data (education records, dementia diagnoses, and mortality) and the Danish Conscription Database (youth intelligence measurements for 854 men). Word recall and verbal fluency were assessed up to 4 times over 10 years (2004-2013) and combined by averaging the z scores. We fitted a joint model linking a time-to-event model for dementia or death to a linear mixed-effects model for cognitive change. Rate of cognitive decline was slower among people with high education compared with low education (β = 0.112, 95% confidence interval (CI): 0.056, 0.170). Adjusting for youth intelligence did not attenuate the association between education and cognitive decline (crude β = 0.136, 95% CI: 0.028, 0.244 vs. adjusted β = 0.145, 95% CI: 0.022, 0.269). The results suggest that higher education may slow cognitive decline in later life. In this sample, results changed little when accounting for selective attrition and confounding by intelligence.