Here, we present a mechanistically grounded theory detailing a novel function of the behavioral immune system (BIS), the psychological system that prompts pathogen avoidance behaviors. We propose that BIS activity allows the body to downregulate basal inflammation, preventing resultant oxidative damage to DNA and promoting longevity. Study 1 investigated the relationship between a trait measure of pathogen avoidance motivation and in vitro and in vivo proinflammatory cytokine production. Study 2 examined the relationship between this same predictor and DNA damage often associated with prolonged inflammation. Results revealed that greater trait pathogen avoidance motivation predicts a) lower levels of spontaneous (but not stimulated) proinflammatory cytokine release by peripheral blood mononuclear cells (PBMCs), b) lower plasma levels of the proinflammatory cytokine interleukin-6 (IL-6), and c) lower levels of oxidative DNA damage. Thus, the BIS may promote health by protecting the body from the deleterious effects of inflammation and oxidative stress.

It is currently unclear whether early life stress (ELS) affects males and females differently. However, a growing body of work has shown that sex moderates responses to stress and injury, with important insights into sex-specific mechanisms provided by work in rodents. Unfortunately, most of the ELS studies in rodents were conducted only in males, a bias that is particularly notable in translational work that has used human imaging. Here we examine the effects of unpredictable postnatal stress (UPS), a mouse model of complex ELS, using high resolution diffusion magnetic resonance imaging. We show that UPS induces several neuroanatomical alterations that were seen in both sexes and resemble those reported in humans. In contrast, exposure to UPS induced fronto-limbic hyper-connectivity in males, but either no change or hypoconnectivity in females. Moderated-mediation analysis found that these sex-specific changes are likely to alter contextual freezing behavior in males but not in females.

Risk perception and consequently engagement in behaviors to avoid illness often do not match actual risk of infection, morbidity, and mortality. Unrealistic optimism occurs when individuals falsely believe that their personal outcomes will be more favorable than others' in the same risk category. Natural selection could favor overconfidence if its benefits, such as psychological resilience, outweigh its costs. However, just because optimism biases may have offered fitness advantages in our evolutionary past does not mean that they are always optimal. The current project examined relationships among personal risk for severe COVID-19, risk perceptions, and preventative behaviors. We predicted that those with higher risk of severe COVID-19 would exhibit unrealistic optimism and behave in ways inconsistent with their elevated risk of morbidity and mortality. Clinical risk scores for severe COVID-19 were calculated and compared with COVID-19 threat appraisal, compliance with shelter-in-place orders (March 13–May 22, 2020) and travel restrictions, compliance with public health recommendations, and potential covariates like self-rated knowledge about COVID-19 in a robust dataset including 492 participants from McLennan County, TX, USA. While those with high clinical risk acknowledged their greater likelihood of experiencing severe illness if infected, they actually reported lower perceived likelihood of becoming infected in the first place. While it is possible that those with higher clinical risk scores truly are less likely to become infected, the pattern and significance of these results held after controlling for possible occupational exposure, household size, and other factors related to infection probability. Higher clinical risk also predicted more recent travel within Texas and lower distress during the pandemic (i.e., feeling less stressed, depressed, and helpless). Additional behavioral data suggested that those with higher clinical risk scores did not generally behave differently than those with lower scores during the shelter-in-place order. While unrealistic optimism may provide some short-term psychological benefits, it could be dangerous due to improper assessment of hazardous situations; inferring that optimism bias has evolutionary origins does not mean that unrealistic optimism is “optimal” in every situation. This may be especially true when individuals face novel sources (or scales) of risk, such as a global pandemic.

Here, we propose a novel theoretical model linking present-focused decision-making to the activities of the immune system. We tested our model by examining the relationship between inflammatory activity – in vivo and in vitro – and decision-making characterized by impulsivity, present focus, and an inability to delay gratification. Results support our model, revealing that inflammation predicts these outcomes even after controlling for factors that may contribute to a spurious linkage between them. Moreover, subsequent analyses revealed that our model was a better fit for the data than alternative models using present-focused decision-making and its health-harming behavioural sequelae (e.g., smoking, risky sexual behaviour) to predict inflammation, lending support for the proposed directionality of this relationship. Together, these results suggest that inflammation may contribute to decision-making patterns that can result in undesirable personal and societal outcomes.

Although frequently characterized as undesirable, risk-taking is an integral part of human social life. Research into the factors that influence risk-taking therefore represents an important area of study in the evolutionary sciences. The current research draws from research on humans' pathogen avoidance psychology, life history theory, and sickness behavior to examine the role that pathogen threat plays in modulating risk tolerance. Across 4 studies, we measured or manipulated pathogen threat cues and examined their effect on risk tolerance. Results revealed a consistent pattern whereby people preferred less risk when the threat of illness was high. This pattern was observed using both self-report measures and behavioral assays but was eliminated when the threat was experimentally minimized. The current research provides evidence of a conceptual link between pathogen threats and global tolerance for risk, demonstrating a tendency to play it safe when the threat of illness is high. Public Significance StatementThe current research examined how pathogen threats influence the psychology governing risk-taking. Four experimental studies found that when pathogen threats are made salient, people exhibit decreased willingness to take risks across domains (e.g., financial, social, health) and take fewer risks during a behavioral task. Results provide preliminary evidence that humans' pathogen management psychology may play an important role in modulating risk preferences in a variety of domains.

A growing body of research finds that the activities of the immune system—in addition to protecting the body from infection and injury—also influence how we think, feel, and behave. Although research on the relationship between the immune system and psychological and behavioral outcomes has most commonly focused on the experiences of those who are ill or experiencing an acute immune response, we propose that the immune system may also play a key role in influencing such outcomes in those who are healthy. Here, we review theory and research suggesting that inflammation—a key component of the immune response to pathogens and stressors—may play an important modulatory role in shaping emotions, motivation, cognition, and behavior, even among those without symptoms of illness. Moreover, because inflammation occurs in response to a number of everyday social experiences (e.g., loneliness and stress), we propose that it may be an important mediator of many psychological and behavioral outcomes that are of interest to social and personality psychologists. We close by discussing potential opportunities for researchers looking to incorporate psychoneuroimmunology (PNI) into their area of inquiry.

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This a preprint and has not been peer reviewed. Data may be preliminary.