Hashemi, M. M. | bioRxiv Science

bioRxiv2019

Human defensive freezing is associated with acute threat coping, long term hair cortisol levels and trait anxiety.

The detection and anticipation of threat facilitates innate defensive behaviours including freezing reactions. Freezing in humans is characterized by reductions in body sway and heart rate and limited evidence suggests that individual differences in freezing reactions are associated with hypothalamic-pituitary-adrenal (HPA) axis activity and anxiety. However, previous measurements of human freezing reactions were largely based on passive threat contexts where natural variations in adaptive threat coping could not be assessed. In a well powered sample (N=419), we studied individual differences in anticipatory freezing reactions, by measuring body sway and heart rate, during an active shooting task where shooting decisions had to be taken under threat of shock. We linked freezing measures to subsequent actions and predictors of anxiety-related psychopathology, including accumulated long-term (3 months) hair cortisol concentrations (HCC) and trait anxiety. The anticipation of threat of shock elicited significant body sway- and heart rate reductions consistent with freezing. Whereas both freezing-related reductions in body sway and heart rate were associated with faster correct shooting decisions, body sway reductions were additionally related to more impulsive shooting (false alarms). Individual differences in threat-related reductions in body sway but not heart rate were further associated to lower HCC and higher trait anxiety. The observed links between freezing and subsequent defensive actions as well as predictors of stress-related psychopathology suggest the potential value of defensive freezing reactions as somatic marker for stress-vulnerability and resilience.

physiology↗

bioRxiv2017

Dopaminergic drug effects on probability weighting during risky decision-making

Dopamine has been associated with risky decision-making, as well as with pathological gambling, a behavioural addiction characterized by excessive risk-taking behaviour. However, the specific mechanisms through which dopamine might act to foster risk-taking and pathological gambling remain elusive. Here we test the hypothesis that this might be achieved, in part, via modulation of subjective probability weighing during decision-making. Healthy controls (n = 21) and pathological gamblers (n = 16) played a decision-making task involving choices between sure monetary options and risky gambles both in the gain and loss domains. Each participant played the task twice, either under placebo or the dopamine D2/D3 receptor antagonist sulpiride, in a double-blind, counter-balanced, design. A prospect theory modelling approach was used to estimate subjective probability weighting and sensitivity to monetary outcomes. Consistent with prospect theory, we found that participants presented a distortion in the subjective weighting of probabilities, i.e. they overweighted low probabilities and underweighted moderate to high probabilities, both in the gain and loss domains. Compared with placebo, sulpiride attenuated this distortion in the gain domain. Across drugs, the groups did not differ in their probability weighting, although in the placebo condition, gamblers consistently underweighted losing probabilities. Overall, our results reveal that dopamine D2/D3 receptor antagonism modulates the subjective weighting of probabilities in the gain domain, in the direction of more objective, economically rational decision-making.\n\nSignificance statementDopamine has been implicated in risky decision-making and gambling addiction, but the exact mechanisms underlying this influence remain partly elusive. Here we tested the hypothesis that dopamine modulates subjective probability weighting, by examining the effect of a dopaminergic drug on risk-taking behaviour, both in healthy individuals and pathological gamblers. We found that selectively blocking dopamine D2/D3 receptors diminished the typically observed distortion of winning probabilities, characterized by an overweighting of low probabilities and underweighting of high probabilities. This made participants more linear in their subjective estimation of probabilities, and thus more rational in their decision-making behaviour. Healthy participants and pathological gamblers did not differ in their risk-taking behaviour, except in the placebo condition in which gamblers consistently underweighted losing probabilities.

neuroscience↗