Heterogeneity of depression across the socioeconomic spectrum.

Why is lower socioeconomic status associated with higher rates of depression? And, is the surplus of depression at lower SES just more of the same type as depression found at higher levels, or is it distinctive? We addressed these questions by examining the relations among SES, amygdala volume, and symptoms of depression in healthy young adults. Amygdala volume, a risk factor for depression, does not synergize with SES in a diathesis-stress relation, nor does it mediate the relation of SES to depression. Rather, SES and amygdala volume are independent, additive risk factors. They are also associated with different depression symptoms and, whereas perceived stress fully mediates the relation of SES to depression, it has no relation to amygdala volume. These findings suggest heterogeneity of depression across the socioeconomic spectrum, with implications for treatment selection as well as for future genetic and brain studies.

Reflections on the past two decades of neuroscience.

The first issue of Nature Reviews Neuroscience was published 20 years ago, in 2000. To mark this anniversary, in this Viewpoint article we asked a selection of researchers from across the field who have authored pieces published in the journal in recent years for their thoughts on notable and interesting developments in neuroscience, and particularly in their areas of the field, over the past two decades. They also provide some thoughts on current lines of research and questions that excite them.

Socioeconomic status and the brain: prospects for neuroscience-informed policy.

Socioeconomic status (SES) is associated with health (physical and mental) and cognitive ability. Understanding and ameliorating the problems of low SES have long been goals of economics and sociology; in recent years, these have also become goals of neuroscience. However, opinion varies widely on the relevance of neuroscience to SES-related policy. The present article addresses the question of whether and how neuroscience can contribute to the development of social policy concerning poverty and the social and ethical risks inherent in trying. I argue that the neuroscience approach to SES-related policy has been both prematurely celebrated and peremptorily dismissed and that some of its possible social impacts have been viewed with excessive alarm. Neuroscience has already made modest contributions to SES-related policy, and its potential to have a more effective and beneficial influence can be expected to grow over the coming years.

Introduction to the Special Focus: The Affective Neuroscience of Poverty.

Growing up in poverty is associated with a heightened risk for mental and physical health problems across the life span, and there is a growing recognition of the role that social determinants of health play in driving these outcomes and inequities. How do the social conditions of poverty get under the skin to influence biology, and through what mechanisms do the stressors of poverty generate risk for a broad range of health problems? The growing field examining the neuroscience of socioeconomic status (SES) proposes that the brain is an entry point or pathway through which poverty and adversity become embedded in biology to generate these disparities. To date, however, the majority of research on the neuroscience of SES has focused on cognitive or executive control processes. However, the relationship between SES and brain systems involved in affective or emotional processes may be especially important for understanding social determinants of health. Accordingly, this Special Focus on The Affective Neuroscience of Poverty invited contributions from authors examining the relationship between SES and brain systems involved in generating and regulating emotions. In this editorial introduction, we (a) provide an overview of the neuroscience of SES; (b) introduce each of the articles in this Special Focus; and (c) discuss the scientific, treatment, and policy implications of studying the affective neuroscience of poverty.

Anger, Fear, and Sadness: Relations to Socioeconomic Status and the Amygdala.

Here, we test three often proposed hypotheses about socioeconomic status (SES), affect, and the brain, for which evidence is mixed or lacking. The first hypothesis, that negative affect is more common at lower levels of SES, has ample evidence from studies of psychiatric symptoms but is tested for the first time here across multiple measures of negative emotions in healthy young adults. The second hypothesis is actually a set of hypotheses, that SES is associated with three structural and functional properties of the amygdala. Third, and most important for the affective neuroscience of SES, is the hypothesis that SES differences in the amygdala are responsible for the affective differences. Despite the intuitive appeal of this hypothesis, it has rarely been tested and has never been confirmed. Here, we review the literature for evidence on each of these hypotheses and find in a number of cases that the evidence is weak or nonexistant. We then subject each hypothesis to a new empirical test with a large sample of healthy young adults. We confirm that negative affect is more common at lower levels of SES and we find a positive relation between SES and amygdala volume. However, evidence is weak on the relation of SES to functional properties of amygdala. Finally, the tendency toward negative affect in lower SES individuals cannot be accounted for by the structural or functional characteristics of the amygdala measured here.

Randomized Manipulation of Early Cognitive Experience Impacts Adult Brain Structure.

Does early exposure to cognitive and linguistic stimulation impact brain structure? Or do genetic predispositions account for the co-occurrence of certain neuroanatomical phenotypes and a tendency to engage children in cognitively stimulating activities? Low socioeconomic status infants were randomized to either 5 years of cognitively and linguistically stimulating center-based care or a comparison condition. The intervention resulted in large and statistically significant changes in brain structure measured in midlife, particularly for male individuals. These findings are the first to extend the large literature on cognitive enrichment effects on animal brains to humans, and to demonstrate the effects of uniquely human features such as linguistic stimulation.

Early childhood poverty and adult executive functioning: Distinct, mediating pathways for different domains of executive functioning.

Executive functioning in adulthood is associated with early-in-life disadvantage. Furthermore, distinct and independent underlying processes account for differences in specific domains of adult executive functioning. The duration of poverty from birth to age 9 is associated with reduced adult inhibitory control assessed by the Flanker task (n = 233, M = 23.52 years). This effect is largely explained by lower levels of maternal responsiveness in adolescence. Early poverty also related to worse working memory in adulthood, and this effect is partially explained by elevated allostatic load during adolescence, an index of chronic physiological stress.

Progress and challenges in probing the human brain.

Perhaps one of the greatest scientific challenges is to understand the human brain. Here we review current methods in human neuroscience, highlighting the ways that they have been used to study the neural bases of the human mind. We begin with a consideration of different levels of description relevant to human neuroscience, from molecules to large-scale networks, and then review the methods that probe these levels and the ability of these methods to test hypotheses about causal mechanisms. Functional MRI is considered in particular detail, as it has been responsible for much of the recent growth of human neuroscience research. We briefly review its inferential strengths and weaknesses and present examples of new analytic approaches that allow inferences beyond simple localization of psychological processes. Finally, we review the prospects for real-world applications and new scientific challenges for human neuroscience.

Functional MRI-based lie detection: scientific and societal challenges.

Functional MRI (fMRI)-based lie detection has been marketed as a tool for enhancing personnel selection, strengthening national security and protecting personal reputations, and at least three US courts have been asked to admit the results of lie detection scans as evidence during trials. How well does fMRI-based lie detection perform, and how should the courts, and society more generally, respond? Here, we address various questions ­ some of which are based on a meta-analysis of published studies ­ concerning the scientific state of the art in fMRI-based lie detection and its legal status, and discuss broader ethical and societal implications. We close with three general policy recommendations.

A meta-analysis of the relationship between socioeconomic status and executive function performance among children.

The relationship between childhood socioeconomic status (SES) and executive function (EF) has recently attracted attention within psychology, following reports of substantial SES disparities in children's EF. Adding to the importance of this relationship, EF has been proposed as a mediator of socioeconomic disparities in lifelong achievement and health. However, evidence about the relationship between childhood SES and EF is mixed, and there has been no systematic attempt to evaluate this relationship across studies. This meta-analysis systematically reviewed the literature for studies in which samples of children varying in SES were evaluated on EF, including studies with and without primary hypotheses about SES. The analysis included 8760 children between the ages of 2 and 18 gathered from 25 independent samples. Analyses showed a small but statistically significant correlation between SES and EF across all studies (rrandom  = .16, 95% CI [.12, .21]) without correcting for attenuation owing to range restriction or measurement unreliability. Substantial heterogeneity was observed among studies, and a number of factors, including the amount of SES variability in the sample and the number of EF measures used, emerged as moderators. Using only the 15 studies with meaningful SES variability in the sample, the average correlation between SES and EF was small-to-medium in size (rrandom  = .22, 95% CI [.17, .27]). Using only the six studies with multiple measures of EF, the relationship was medium in size (rrandom  = .28, 95% CI [.18, .37]). In sum, this meta-analysis supports the presence of SES disparities in EF and suggests that they are between small and medium in size, depending on the methods used to measure them.

Does Transcranial Direct Current Stimulation Improve Healthy Working Memory?: A Meta-analytic Review.

Transcranial direct current stimulation (tDCS) has been reported to improve working memory (WM) performance in healthy individuals, suggesting its value as a means of cognitive enhancement. However, recent meta-analyses concluded that tDCS has little or no effect on WM in healthy participants. In this article, we review reasons why these meta-analyses may have underestimated the effect of tDCS on WM and report a more comprehensive and arguably more sensitive meta-analysis. Consistent with our interest in enhancement, we focused on anodal stimulation. Thirty-one articles matched inclusion criteria and were included in four primary meta-analyses assessing the WM effects of anodal stimulation over the left and right dorsolateral pFC (DLPFC) and right parietal lobe as well as left DLPFC stimulation coupled with WM training. These analyses revealed a small but significant effect of left DLPFC stimulation coupled with WM training. Left DLPFC stimulation alone also enhanced WM performance, but the effect was reduced to nonsignificance after correction for publication bias. No other effects were significant, including a variety of tested moderators. Additional meta-analyses were undertaken with study selection criteria based on previous meta-analyses, to reassess the findings from these studies using the analytic methods of this study. These analyses revealed a mix of significant and nonsignificant small effects. We conclude that the primary WM enhancement potential of tDCS probably lies in its use during training.

Effect of socioeconomic status (SES) disparity on neural development in female African-American infants at age 1 month.

There is increasing interest in both the cumulative and long-term impact of early life adversity on brain structure and function, especially as the brain is both highly vulnerable and highly adaptive during childhood. Relationships between SES and neural development have been shown in children older than age 2 years. Less is known regarding the impact of SES on neural development in children before age 2. This paper examines the effect of SES, indexed by income-to-needs (ITN) and maternal education, on cortical gray, deep gray, and white matter volumes in term, healthy, appropriate for gestational age, African-American, female infants. At 5 weeks postnatal age, unsedated infants underwent MRI (3.0T Siemens Verio scanner, 32-channel head coil). Images were segmented based on a locally constructed template. Utilizing hierarchical linear regression, SES effects on MRI volumes were examined. In this cohort of healthy African-American female infants of varying SES, lower SES was associated with smaller cortical gray and deep gray matter volumes. These SES effects on neural outcome at such a young age build on similar studies of older children, suggesting that the biological embedding of adversity may occur very early in development.

Prescription Stimulants' Effects on Healthy Inhibitory Control, Working Memory, and Episodic Memory: A Meta-analysis.

The use of prescription stimulants to enhance healthy cognition has significant social, ethical, and public health implications. The large number of enhancement users across various ages and occupations emphasizes the importance of examining these drugs' efficacy in a nonclinical sample. The present meta-analysis was conducted to estimate the magnitude of the effects of methylphenidate and amphetamine on cognitive functions central to academic and occupational functioning, including inhibitory control, working memory, short-term episodic memory, and delayed episodic memory. In addition, we examined the evidence for publication bias. Forty-eight studies (total of 1,409 participants) were included in the analyses. We found evidence for small but significant stimulant enhancement effects on inhibitory control and short-term episodic memory. Small effects on working memory reached significance, based on one of our two analytical approaches. Effects on delayed episodic memory were medium in size. However, because the effects on long-term and working memory were qualified by evidence for publication bias, we conclude that the effect of amphetamine and methylphenidate on the examined facets of healthy cognition is probably modest overall. In some situations, a small advantage may be valuable, although it is also possible that healthy users resort to stimulants to enhance their energy and motivation more than their cognition.

Socioeconomic status and the brain: mechanistic insights from human and animal research.

Human brain development occurs within a socioeconomic context and childhood socioeconomic status (SES) influences neural development--particularly of the systems that subserve language and executive function. Research in humans and in animal models has implicated prenatal factors, parent-child interactions and cognitive stimulation in the home environment in the effects of SES on neural development. These findings provide a unique opportunity for understanding how environmental factors can lead to individual differences in brain development, and for improving the programmes and policies that are designed to alleviate SES-related disparities in mental health and academic achievement.

Socioeconomic status and executive function: developmental trajectories and mediation.

Childhood socioeconomic status (SES) predicts executive function (EF), but fundamental aspects of this relation remain unknown: the developmental course of the SES disparity, its continued sensitivity to SES changes during that course, and the features of childhood experience responsible for the SES-EF relation. Regarding course, early disparities would be expected to grow during development if caused by accumulating stressors at a given constant level of SES. Alternatively, they would narrow if schooling partly compensates for the effects of earlier deprivation, allowing lower-SES children to 'catch up'. The potential for later childhood SES change to affect EF is also unknown. Regarding mediating factors, previous analyses produced mixed answers, possibly due to correlation amongst candidate mediators. We address these issues with measures of SES, working memory and planning, along with multiple candidate mediators, from the NICHD Study of Early Childcare (n = 1009). Early family income-to-needs and maternal education predicted planning by first grade, and income-to-needs predicted working memory performance at 54 months. Effects of early SES remained consistent through middle childhood, indicating that the relation between early indicators of SES and EF emerges in childhood and persists without narrowing or widening across early and middle childhood. Changes in family income-to-needs were associated with significant changes in planning and trend-level changes in working memory. Mediation analyses supported the role of early childhood home characteristics in explaining the association between SES and EF, while early childhood maternal sensitivity was specifically implicated in the association between maternal education and planning. Early emerging and persistent SES-related differences in EF, partially explained by characteristics of the home and family environment, are thus a potential source of socioeconomic disparities in achievement and health across development.

Mapping the trajectory of socioeconomic disparity in working memory: parental and neighborhood factors.

Working memory (WM) is positively correlated with socioeconomic status (SES). It is not clear, however, if SES predicts the rate of WM development over time or whether SES effects are specific to family rather than neighborhood SES. A community sample of children (n = 316) enrolled between ages 10 and 13 completed four annual assessments of WM. Lower parental education, but not neighborhood disadvantage, was associated with worse WM performance. Neither measure of SES was associated with the rate of developmental change. Consequently, the SES disparity in WM is not a developmental lag that narrows or an accumulating effect that becomes more pronounced. Rather, the relation between family SES and WM originates earlier in childhood and is stable through adolescence.

Brain images, babies, and bathwater: critiquing critiques of functional neuroimaging.

Since the mid-1980s, psychologists and neuroscientists have used brain imaging to test hypotheses about human thought processes and their neural instantiation. In just three decades, functional neuroimaging has been transformed from a crude clinical tool to a widely used research method for understanding the human brain and mind. Such rapidly achieved success is bound to evoke skepticism. A degree of skepticism toward new methods and ideas is both inevitable and useful in any field. It is especially valuable in a science as young as cognitive neuroscience and its even younger siblings, social and affective neuroscience. Healthy skepticism encourages us to check our assumptions, recognize the limitations of our methods, and proceed thoughtfully. Skepticism itself, however, also must be examined. In this article, I review the most commonly voiced criticisms of functional neuroimaging. In the spirit of healthy skepticism, I will critically examine these criticisms themselves. Each contains at least a kernel of truth, although I will argue that in some cases the kernel has been over extended in ways that are inaccurate or misleading.

Ethical, legal, and policy challenges in field-based neuroimaging research using emerging portable MRI technologies: guidance for investigators and for oversight.

Researchers are rapidly developing and deploying highly portable MRI technology to conduct field-based research. The new technology will widen access to include new investigators in remote and unconventional settings and will facilitate greater inclusion of rural, economically disadvantaged, and historically underrepresented populations. To address the ethical, legal, and societal issues raised by highly accessible and portable MRI, an interdisciplinary Working Group (WG) engaged in a multi-year structured process of analysis and consensus building, informed by empirical research on the perspectives of experts and the general public. This article presents the WG's consensus recommendations. These recommendations address technology quality control, design and oversight of research, including safety of research participants and others in the scanning environment, engagement of diverse participants, therapeutic misconception, use of artificial intelligence algorithms to acquire and analyze MRI data, data privacy and security, return of results and managing incidental findings, and research participant data access and control.

Look again: effects of brain images and mind-brain dualism on lay evaluations of research.

Brain scans have frequently been credited with uniquely seductive and persuasive qualities, leading to claims that fMRI research receives a disproportionate share of public attention and funding. It has been suggested that functional brain images are fascinating because they contradict dualist beliefs regarding the relationship between the body and the mind. Although previous research has indicated that brain images can increase judgments of an article's scientific reasoning, the hypotheses that brain scans make research appear more interesting, surprising, or worthy of funding have not been tested. Neither has the relation between the allure of brain imaging and dualism. In the following three studies, laypersons rated both fictional research descriptions and real science news articles accompanied by brain scans, bar charts, or photographs. Across 988 participants, we found little evidence of neuroimaging's seductive allure or of its relation to self-professed dualistic beliefs. These results, taken together with other recent null findings, suggest that brain images are less powerful than has been argued.