Now or Later? Stress-Induced Increase and Decrease in Choice Impulsivity Are Both Associated with Elevated Affective and Endocrine Responses

The impact of methylphenidate on choice impulsivity is inversely associated with corpus callosum fiber integrity across sexes

BACKGROUND

Choice impulsivity represents preference towards smaller immediate rewards over larger delayed rewards. Extensive literature demonstrates that choice impulsivity can be manipulated using dopaminergic agonists such as methylphenidate (MPH), and that females exhibit elevated choice impulsivity compared to males. Sex differences are also frequently reported with respect to brain white matter (WM) fiber integrity. It has yet to be determined whether sex differences also exist in the impact of MPH on choice impulsivity, and whether these putative differences are accounted for by the integrity of differential WM fibers.

METHODS

Forty-eight healthy young adults completed the delay discounting (DD) task twice during MRI-DTI scans after receiving either MPH or placebo in a double-blind, placebo-controlled, within-subject design. WM fiber integrity was assessed using automated fiber quantification (AFQ) and tract-based spatial statistics (TBSS).

RESULTS

Compared to placebo, MPH yielded significantly reduced choice impulsivity in males but not in females. DTI data revealed reduced integrity in multiple WM fibers in females compared to males. Interestingly, the impact of MPH on choice impulsivity was negatively associated with fiber integrity in the forceps major of the corpus callosum for males only and positively associated with fiber integrity in the forceps minor of the corpus callosum for females only.

CONCLUSIONS

Taken together, results uncover sex-specific effects of MPH on choice impulsivity, accounted for by inverse associations between choice impulsivity under MPH and the structural integrity of distinct segments of the corpus callosum. These findings highlight the need to consider sex differences in the neurobiological mechanisms of impulsivity.

Stress and episodic future thinking: Effects on temporal window and alcohol demand

BACKGROUND

Stress maintains problematic alcohol use, so it is particularly important to identify interventions that effectively reduce the desire for alcohol even in the context of high stress. Reinforcer Pathology Theory suggests that stress increases alcohol demand by inducing short-term thinking. One intervention that targets this mechanism is episodic future thinking (EFT), which involves vividly imagining personal future events and has been shown to reduce short-term thinking and accompanying preferences for immediate rewards like alcohol. These shared mechanisms suggest that EFT may be particularly effective at reducing alcohol demand in the context of higher stress. This study first assessed the relationship of stress with preference for immediate rewards and alcohol demand, and the impact of EFT on preference for immediate rewards and alcohol demand. This study then tested whether EFT may be particularly effective in the context of higher stress.

METHODS

One hundred thirty-nine adults with problematic alcohol use completed an online survey through Amazon Mechanical Turk (MTurk), including self-report measures of past month stress and baseline momentary stress, an EFT or episodic recent thinking (ERT) procedure, a delay-discounting task, and an alcohol purchase task. Univariate correlations assessed the relationship of stress with delay discounting and alcohol demand intensity. Path analyses assessed hypothesized models relating EFT/ERT, stress, delay discounting, and demand intensity.

RESULTS

Consistent with Reinforcer Pathology Theory, higher baseline momentary stress was correlated with increased preference for immediate rewards. EFT intervention increased preference for delayed rewards, which contributed to decreased alcohol demand. However, the effect of EFT on delay discounting was not moderated by stress.

CONCLUSIONS

EFT does not appear uniquely effective at reducing desire for alcohol in the context of higher stress, but equally, EFT's efficacy was not significantly affected by stress level. Findings emphasize the opposing roles of state stress and EFT in the behavioral economics underlying problematic alcohol use.

Dynamics in physiological acute stress response trajectories: uncovering latent variability

BACKGROUND

Acute stressors trigger an immediate physiological response, involving multiple intricating pathways. These adaptive physiological responses include, among other processes, an increase in heart rate (HR) and a decrease in heart rate variability (HRV). Despite substantial efforts, linking individual variability in physiological acute stress response patterns with related psychological constructs such as anxiety and depression remains challenging. Notably, the majority of studies to date treated physiological stress responses as static entities, overlooking putative inter-individual variability in the dynamics at which physiological acute stress response trajectories unfold over-time.

METHODS

To address this gap, physiological responses (HR and HRV) were continuously recorded from 78 healthy adult female participants during an established 10-min-long laboratory acute stress induction manipulation. These physiological responses were separately quantified for three consecutive 3.3-min-long segments that together encompass the entire acute stress procedure, as well as for the 3.3-min-long segments immediately before and after stress.

RESULTS

At the whole group level stress was found to immediately increase HR, while HRV showed a delayed decrease with a post-stress overshoot effect. Latent class modeling revealed subgroups with unique physiological response trajectories, including a subset of participants that exhibited an atypical increase in HRV during stress. These individuals also exhibited elevated anxiety levels.

CONCLUSIONS

Results underscore the complexity of physiological responses to acute stress and suggest that a dynamic approach could contribute to our understanding of the interplay between physiological stress responses and related psychological constructs. Further research is needed to replicate these findings and explore putative implications for stress-related mental health conditions.

Hunger Games: A Modern Battle Between Stress and Appetite

Stress, an evolutionarily adaptive mechanism, has become a pervasive challenge in modern life, significantly impacting feeding-relevant circuits that play a role in the development and pathogenesis of eating disorders (EDs). Stress activates the hypothalamic-pituitary-adrenal (HPA) axis, disrupts specific neural circuits, and dysregulates key brain regions, including the hypothalamus, hippocampus, and lateral septum. These particular structures are interconnected and key in integrating stress and feeding signals, modulating hunger, satiety, cognition, and emotional coping behaviors. Here we discuss the interplay between genetic predispositions and environmental factors that may exacerbate ED vulnerability. We also highlight the most commonly used animal models to study the mechanisms driving EDs and recent rodent studies that emphasize the discovery of novel cellular and molecular mechanisms integrating stress and feeding signals within the hippocampus-lateral septum-hypothalamus axis. In this review, we discuss the role of gut microbiome, an emerging area of research in the field of EDs and unanswered questions that persist and hinder the scientific progress, such as why some individuals remain resilient to stress while others become at high risk for the development of EDs. We finally discuss the need for future research delineating the impact of specific stressors on neural circuits, clarifying the relevance and functionality of hippocampal-septal-hypothalamic connectivity, and investigating the role of key neuropeptides such as CRH, oxytocin, and GLP-1 in human ED pathogenesis. Emerging tools like single-cell sequencing and advanced human imaging could uncover cellular and circuit-level changes in brain areas relevant for feeding in ED patients. Ultimately, by integrating basic and clinical research, science offers promising avenues for developing personalized, mechanism-based treatments targeting maladaptive eating behavior for patients suffering from EDs.

Behavioural profiling following acute stress uncovers associations with future stress sensitivity and past childhood abuse

Background: Individuals greatly differ in their responses to acute stress, ranging from resilience to vulnerability that may yield stress-related psychopathology. Stress-related psychopathologies involve, by definition, substantial modifications across multiple behavioural domains, including impaired cognitive, affective and social functioning. Nevertheless, and despite extensive investigation of individual variability in stress responsivity, no study to date simultaneously assessed the impact of acute stress across multiple behavioural domains within a given individual.Objective: To address this critical gap, 84 healthy female participants (mean age 24.45 ± 3.02, range 19-35) underwent an established acute stress induction procedure and completed three behavioural tasks, probing the functional domains of positive, cognitive and social processing, both before and after the acute stress procedure.Method: A novel behavioural profiling algorithm was implemented to identify individuals whose performance was substantially impacted by stress across all three functional domains.Results: Approximately 30% of participants exhibited substantial deviation in their performance from before to after stress in all three tasks, hereon defined as stress-affected. Stress-affected participants did not differ in their psychological and physiological responses to the acute stress procedure from the other stress-unaffected 70% of the sample. However, follow-up assessments in 66 of these participants revealed higher levels of stress six months following the procedure among the stress-affected compared to the stress-unaffected group. Stress-affected individuals also reported more aversive childhood experiences, such that the odds of participants who were sexually abused at an early age to be affected behaviourally by acute stress later in life increased by more than five-fold.Conclusions: Taken together, these findings suggest that being affected by acute stress across multiple functional domains is associated with future stress sensitivity and past childhood sexual abuse. Probing individual differences in the impact of acute stress across domains of functionality may better align with the multi-dimensional nature of stress responsivity, uncovering latent vulnerability.

A multinational analysis of how emotions relate to economic decisions regarding time or risk

Emotions have been theorized to be important drivers of economic choices, such as intertemporal or risky decisions. Our systematic review and meta-analysis of the previous literature (378 results and 50,972 participants) indicates that the empirical basis for these claims is mixed and the cross-cultural generalizability of these claims has yet to be systematically tested. We analysed a dataset with representative samples from 74 countries (n = 77,242), providing a multinational test of theoretical claims that individuals' ongoing emotional states predict their economic preferences regarding time or risk. Overall, more positive self-reported emotions generally predicted a willingness to wait for delayed rewards or to take favourable risks, in line with some existing theories. Contrary to the assumption of a universal relationship between emotions and decision-making, we show that these relationships vary substantially and systematically across countries. Emotions were stronger predictors of economic decisions in more economically developed and individualistic countries.

The effects of threat on complex decision-making: evidence from a virtual environment

Individuals living and working in dangerous settings (e.g., first responders and military personnel) make complex decisions amidst serious threats. However, controlled studies on decision-making under threat are limited given obvious ethical concerns. Here, we embed a complex decision-making task within a threatening, immersive virtual environment. Based on the Iowa Gambling Task (IGT), a paradigm widely used to study complex decision-making, the task requires participants to make a series of choices to escape a collapsing building. In Study 1 we demonstrate that, as with the traditional IGT, participants learn to make advantageous decisions over time and that their behavioural data can be described by reinforcement-learning based computational models. In Study 2 we created threatening and neutral versions of the environment. In the threat condition, participants performed worse, taking longer to improve from baseline and scoring lower through the final trials. Computational modelling further revealed that participants in the threat condition were more responsive to short term rewards and less likely to perseverate on a given choice. These findings suggest that when threat is integral to decision-making, individuals make more erratic choices and focus on short term gains. They furthermore demonstrate the utility of virtual environments for making threat integral to cognitive tasks.

No effects of acute stress on monetary delay discounting: A systematic literature review and meta-analysis

Many everyday decisions, including those concerning our health, finances and the environment, involve choosing between a smaller but imminent reward (e.g., €20 now) and a later but larger reward (e.g., €40 in a month). The extent to which an individual prefers smaller imminent rewards over larger delayed rewards can be measured using delay discounting tasks. Acute stress induces a cascade of biological and psychological responses with potential consequences for how individuals think about the future, process rewards, and make decisions, all of which can impact delay discounting. Several studies have shown that individuals focus more on imminent rewards under stress. These findings have been used to explain why individuals make detrimental choices under acute stress. Yet, the evidence linking acute stress to delay discounting is equivocal. To address this uncertainty, we conducted a meta-analysis of 11 studies (14 effects) to systematically quantify the effects of acute stress on monetary delay discounting. Overall, we find no effect of acute stress on delay discounting, compared to control conditions (SMD = -0.18, 95% CI [-0.57, 0.20], p = 0.32). We also find that neither the gender/sex of the participants, the type of stressor (e.g., physical vs. psychosocial) nor whether monetary decisions were hypothetical or incentivized (i.e. monetary decisions were actually paid out) moderated the impact of acute stress on monetary delay discounting. We argue that establishing the effects of acute stress on the separate processes involved in delay discounting, such as reward valuation and prospection, will help to resolve the inconsistencies in the field.

Choice impulsivity after repeated social stress is associated with increased perineuronal nets in the medial prefrontal cortex

Repeated stress can predispose to substance abuse. However, behavioral and neurobiological adaptations that link stress to substance abuse remain unclear. This study investigates whether intermittent social defeat (ISD), a stress protocol that promotes drug-seeking behavior, alters intertemporal decision-making and cortical inhibitory function in the medial prefrontal cortex (mPFC). Male long evans rats were trained in a delay discounting task (DDT) where rats make a choice between a fast (1 s) small reward (1 sugar pellet) and a large reward (3 sugar pellets) that comes with a time delay (10 s or 20 s). A decreased preference for delayed rewards was used as an index of choice impulsivity. Rats were exposed to ISD and tested in the DDT 24 h after each stress episode, and one- and two-weeks after the last stress episode. Immunohistochemistry was performed in rat's brains to evaluate perineuronal nets (PNNs) and parvalbumin GABA interneurons (PV) labeling as markers of inhibitory function in mPFC. ISD significantly decreased the preference for delayed large rewards in low impulsive, but not high impulsive, animals. ISD also increased the density of PNNs in the mPFC. These results suggest that increased choice impulsivity and cortical inhibition predispose animals to seek out rewards after stress.

Effects of stress on endophenotypes of suicide across species: A role for ketamine in risk mitigation

Suicide is a leading cause of death and morbidity worldwide, yet few interventions are available to mitigate its risk. Barriers to effective treatments involve a limited understanding of factors that predict the onset of suicidal thoughts and behaviors. In the context of suicide risk, stress is a precipitating factor that is largely overlooked in the literature. Indeed, the pathophysiology of stress and suicide are heavily interconnected, underscoring the need to target the stress system in suicide prevention. In this review, we integrate findings from the preclinical and clinical literature that links stress and suicide. We focus specifically on the effects of stress on underlying biological functions and processes associated with suicide, allowing for the review of research using animal models. Owing to the rapid anti-suicidal effects of (R,S)-ketamine, we discuss its ability to modulate various stress-related endophenotypes of suicide, as well as its potential role in preventing suicide in those with a history of chronic life stress (e.g., early life adversity). We highlight future research directions that could advance our understanding of stress-related effects on suicide risk, advocating a dimensional, endophenotype approach to suicide research.

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Suicide and chronic stress pathophysiology are interconnected.

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Chronic stress has profound impacts on several endophenotypes of suicide.

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Animal and human research points to stress as a precipitating factor in suicide.

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Ketamine modulates specific biological processes associated with stress and suicide.

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Suicide research into endophenotypes can help inform risk-mitigation strategies.

Cognitive and Behavioral Patterns across Psychiatric Conditions

Psychiatric conditions represent a highly heterogeneous group of disorders associated with chronic distress and a sharp decline in quality of life [...].