Brain mechanisms mediating effects of stress on reward sensitivity

How developmental neuroscience can help address the problem of child poverty

Nearly 1 in 5 children in the United States lives in a household whose income is below the official federal poverty line, and more than 40% of children live in poor or near-poor households. Research on the effects of poverty on children's development has been a focus of study for many decades and is now increasing as we accumulate more evidence about the implications of poverty. The American Academy of Pediatrics recently added "Poverty and Child Health" to its Agenda for Children to recognize what has now been established as broad and enduring effects of poverty on child development. A recent addition to the field has been the application of neuroscience-based methods. Various techniques including neuroimaging, neuroendocrinology, cognitive psychophysiology, and epigenetics are beginning to document ways in which early experiences of living in poverty affect infant brain development. We discuss whether there are truly worthwhile reasons for adding neuroscience and related biological methods to study child poverty, and how might these perspectives help guide developmentally based and targeted interventions and policies for these children and their families.

Rethinking Concepts and Categories for Understanding the Neurodevelopmental Effects of Childhood Adversity

Discovering the processes through which early adverse experiences affect children's nervous-system development, health, and behavior is critically important for developing effective interventions. However, advances in our understanding of these processes have been constrained by conceptualizations that rely on categories of adversity that are overlapping, have vague boundaries, and lack consistent biological evidence. Here, we discuss central problems in understanding the link between early-life adversity and children's brain development. We conclude by suggesting alternative formulations that hold promise for advancing knowledge about the neurobiological mechanisms through which adversity affects human development.

Regular exposure to a Citrus-based sensory functional food ingredient alleviates the BOLD brain responses to acute pharmacological stress in a pig model of psychosocial chronic stress

Psychosocial chronic stress is a critical risk factor for the development of mood disorders. However, little is known about the consequences of acute stress in the context of chronic stress, and about the related brain responses. In the present study we examined the physio-behavioural effects of a supplementation with a sensory functional food ingredient (FI) containing Citrus sinensis extract (D11399, Phodé, France) in a pig psychosocial chronic stress model. Female pigs underwent a 5- to 6-week stress protocol while receiving daily the FI (FI, n = 10) or a placebo (Sham, n = 10). We performed pharmacological magnetic resonance imaging (phMRI) to study the brain responses to an acute stress (injection of Synacthen^®, a synthetic ACTH-related agonist) and to the FI odour with or without previous chronic supplementation. The olfactory stimulation with the ingredient elicited higher brain responses in FI animals, demonstrating memory retrieval and habituation to the odour. Pharmacological stress with Synacthen injection resulted in an increased activity in several brain regions associated with arousal, associative learning (hippocampus) and cognition (cingulate cortex) in chronically stressed animals. This highlighted the specific impact of acute stress on the brain. These responses were alleviated in animals previously supplemented by the FI during the entire chronic stress exposure. As chronic stress establishes upon the accumulation of acute stress events, any attenuation of the brain responses to acute stress can be interpreted as a beneficial effect, suggesting that FI could be a viable treatment to help individuals coping with repeated stressful events and eventually to reduce chronic stress. This study provides additional evidence on the potential benefits of this FI, of which the long-term consequences in terms of behaviour and physiology need to be further investigated.

Early childhood stress is associated with blunted development of ventral tegmental area functional connectivity

Early life stress increases risk for later psychopathology, due in part to changes in dopaminergic brain systems that support reward processing and motivation. Work in animals has shown that early life stress has a profound impact on the ventral tegmental area (VTA), which provides dopamine to regions including nucleus accumbens (NAcc), anterior hippocampus, and medial prefrontal cortex (mPFC), with cascading effects over the course of development. However, little is known about how early stress exposure shifts the developmental trajectory of mesocorticolimbic circuitry in humans. In the current study, 88 four- to nine-year-old children participated in resting-state fMRI. Parents completed questionnaires on their children's chronic stress exposure, including socioeconomic status (SES) and adverse childhood experiences (ACEs). We found an age x SES interaction on VTA connectivity, such that children from higher SES backgrounds showed a positive relationship between age and VTA-mPFC connectivity. Similarly, we found an age x ACEs exposure interaction on VTA connectivity, such that children with no ACEs exposure showed a positive relationship between age and VTA-mPFC connectivity. Our findings suggest that early stress exposure relates to the blunted maturation of VTA connectivity in young children, which may lead to disrupted reward processing later in childhood and beyond.

Stress and the dopaminergic reward system

Dopamine regulates reward-related behavior through the mesolimbic dopaminergic pathway. Stress affects dopamine levels and dopaminergic neuronal activity in the mesolimbic dopamine system. Changes in mesolimbic dopaminergic neurotransmission are important for coping with stress, as they allow adaption to behavioral responses to various environmental stimuli. Upon stress exposure, modulation of the dopaminergic reward system is necessary for monitoring and selecting the optimal process for coping with stressful situations. Aversive stressful events may negatively regulate the dopaminergic reward system, perturbing reward sensitivity, which is closely associated with chronic stress-induced depression. The mesolimbic dopamine system is excited not only by reward but also by aversive stressful stimuli, which adds further intriguing complexity to the relationship between stress and the reward system. This review focuses on lines of evidence related to how stress, especially chronic stress, affects the mesolimbic dopamine system, and discusses the role of the dopaminergic reward system in chronic stress-induced depression.

Plasticity of the Reward Circuitry After Early-Life Adversity: Mechanisms and Significance

Disrupted operation of the reward circuitry underlies many aspects of affective disorders. Such disruption may manifest as aberrant behavior including risk taking, depression, anhedonia, and addiction. Early-life adversity is a common antecedent of adolescent and adult affective disorders involving the reward circuitry. However, whether early-life adversity influences the maturation and operations of the reward circuitry, and the potential underlying mechanisms, remain unclear. Here, we present novel information using cutting-edge technologies in animal models to dissect out the mechanisms by which early-life adversity provokes dysregulation of the complex interactions of stress and reward circuitries. We propose that certain molecularly defined pathways within the reward circuitry are particularly susceptible to early-life adversity. We examine regions and pathways expressing the stress-sensitive peptide corticotropin-releasing factor (CRF), which has been identified in critical components of the reward circuitry and interacting stress circuits. Notably, CRF is strongly modulated by early-life adversity in several of these brain regions. Focusing on amygdala nuclei and their projections, we provide evidence suggesting that aberrant CRF expression and function may underlie augmented connectivity of the nucleus accumbens with fear/anxiety regions, disrupting the function of this critical locus of pleasure and reward.

Longitudinal Trajectories of Post-Election Distress Track Changes in Neural and Psychological Functioning

The shift in political climate after the 2016 U.S. presidential election had a distressing effect on many individuals. To date, no research has identified how changes in societal-level distressing experiences affected ongoing neurobiological and psychological functioning. Fifty-five participants (M_age = 21.746, 37 women) were tested at two time points. fMRI and psychological measures were used to test the hypotheses that increases in distress over 1 year would relate to worsening mental health symptomology and blunted neurobiological response to reward during the same period. Because individual experiences of distress occurred within a larger macroclimate of societal attitudes, measures were standardized to reflect relative change within the sample. Distress changes over 1 year were positively associated with problematic mental health symptomology and nucleus accumbens (NAcc) response to reward, with dissociable effects for anticipation and outcome. Worsening distress was associated with increased NAcc response to reward anticipation but decreased NAcc response to reward outcome. Individuals who exhibited increased sensitivity to anticipatory reward were those who exhibited more avoidance distress symptoms, whereas intrusion and hyperarousal were associated with decreased sensitivity to reward outcome. This study highlights the importance of considering individual variation in profiles of change in response to ongoing distress, suggests that individual response styles yield differences in reward sensitivity, and extends neurobiological understanding of exposure to stressful life experiences to political events.

Acute stress alters neural patterns of value representation for others

Acute stress is often evoked during social interactions, by feelings of threat or negative evaluation by other people. We also constantly interact with others while under stress - in the workplace or in private alike. However, it is not clear how stress affects social interactions. For one, individuals could become more selfish and focused on their own goals. On the other hand, individuals might also become more focused on affiliating with potential social partners, in order to secure their support. There is, indeed, accumulating behavioral evidence that prosocial behaviors increase rather than decrease under stress. Here, we tested the underlying brain processes of such findings, by assessing the effects of stress on the neural representations of (monetary) value for self and other. Participants (N ​= ​30; male, 18-40 years) played a gambling task for themselves and for another participant while undergoing functional magnetic resonance imaging (fMRI). Each participant played the gambling task twice: once immediately following acute stress induction, and once in a control session. We compared neural patterns of value representation in the dorsomedial prefrontal cortex (dmPFC), ventromedial prefrontal cortex (vmPFC) and striatum using representational similarity analysis (RSA). We found that under stress, dmPFC and striatum showed higher dissimilarity between neural patterns underlying high and low value for the other. Dissimilarity of neural patterns underlying high and low value for the self was unaffected by stress. These findings suggest that participants track the magnitude of possible rewards for others more under stress, suggesting increased prosocial orientation.

Biological bases of suicidal behaviours: A narrative review

Suicidal behaviour is a multifaceted phenomenon that concerns all human populations. It has been suggested that a complex interaction between the individual genetic profile and environmental factors throughout life underlies the pathophysiology of suicidal behaviour. Although epidemiological and genetic studies suggest the existence of a genetic component, exposure to biological and psychosocial adversities, especially during critical developmental periods, also contributes to altering the biological responses to threat and pleasure. This results in amplified maladaptive cognitive and behavioural traits and states associated with suicidal behaviours. Alterations in the cognitive inhibition and decision-making capacity have been implicated in suicidal behaviours. Structural and functional changes in key brain regions and networks, such as prefrontal cortex, insula and default mode network, may underlie this relationship. Furthermore, the shift from health to suicidal behaviour incorporates complex and dynamic changes in the immune and stress responses, monoaminergic system, gonadal system and neuroplasticity. In this review, we describe the major findings of epidemiological, genetic, neuroanatomical, neuropsychological, immunological and neuroendocrinological studies on suicide behaviours to provide a solid background for future research in this field. This broad overview of the biological bases of suicide should promote neuroscience research on suicidal behaviours. This might lead to improved biological models and to the identification of evidence-based biomarkers, treatment options and preventive strategies.

Suicide Has Many Faces, So Does Ketamine: a Narrative Review on Ketamine's Antisuicidal Actions

PURPOSE OF REVIEW

Suicidal behaviours are a challenge for a medical system and public health, partly due to the current lack of evidence-based, effective, rapid tools for suicidal crisis management. Ketamine and its enantiomer esketamine have raised hopes regarding this issue in the recent years. However, their efficacy in suicidal behaviours and mechanisms for it remain a topic of debate.

RECENT FINDINGS

Subanesthetic ketamine doses rapidly, albeit transiently decrease suicidal ideation, with effects emerging within an hour and persisting up to a week. Current evidence points to various and not necessarily exclusive mechanisms for ketamine's antisuicidal action, including effects on neuroplasticity, inflammation, reward system and pain processing. Ketamine rapidly decreases suicidal ideation, but whether it leads to meaningful clinical outcomes past 1 week is unclear. Multiple putative mechanisms drive ketamine's antisuicidal action. Future studies will have to show long-term ketamine treatment outcomes and further elucidate its mechanisms of action.

Bidirectional Associations Between Stress and Reward Processing in Children and Adolescents: A Longitudinal Neuroimaging Study

BACKGROUND

Aberrations in both neural reward processing and stress reactivity are associated with increased risk for mental illness; yet, how these two factors relate to each other remains unclear. Several studies suggest that stress exposure impacts reward function, thus increasing risk for psychopathology. However, the alternative hypothesis, in which reward dysfunction impacts stress reactivity, has been rarely examined. The current study aimed to test both hypotheses using a longitudinal design.

METHODS

Participants were 38 children (23 girls; 61%) from a prospective cohort study. A standard stress-exposure measure was collected at 7 years of age. Children performed a well-validated imaging reward paradigm at age 10, and a standardized acute psychological stress laboratory protocol was administered both at age 10 and at age 13. Structural equation modeling was used to examine bidirectional associations between stress and neural response to reward anticipation.

RESULTS

Higher exposure to stressful life events at age 7 predicted lower neural response to reward anticipation in regions of the basal ganglia at age 10, which included ventral caudate, nucleus accumbens, putamen, and globus pallidus. Lower response to reward anticipation in medial prefrontal and anterior cingulate cortex predicted higher stress reactivity at age 13.

CONCLUSIONS

Our findings provide support for bidirectional associations between stress and reward processing, in that stress may impact reward anticipation, but also in that reduced reward anticipation may increase susceptibility to stress.

Interaction of neurotransmitters and neurochemicals with lymphocytes

Neurotransmitters and neurochemicals can act on lymphocytes by binding to receptors expressed by lymphocytes. This review describes lymphocyte expression of receptors for a selection of neurotransmitters and neurochemicals, the anatomical locations where lymphocytes can interact with neurotransmitters, and the effects of the neurotransmitters on lymphocyte function. Implications for health and disease are also discussed.

From Stress to Anhedonia: Molecular Processes through Functional Circuits

Converging evidence across species highlights the contribution of environmental stress to anhedonia (loss of pleasure and/or motivation). However, despite a clear link between stress and the emergence of anhedonic-like behavior in both human and animal models, the underlying biological pathways remain elusive. Here, we synthesize recent findings across multiple levels, from molecular signaling pathways through whole-brain networks, to discuss mechanisms through which stress may influence anhedonia. Recent work suggests the involvement of diverse systems that converge on the mesolimbic reward pathway, including medial-prefrontal cortical circuitry, neuroendocrine stress responses, homeostatic energy regulation systems, and inflammation. We conclude by emphasizing the need to disentangle the influences of key dimensions of stress on specific aspects of reward processing, taking into account individual differences that could moderate this relationship.