Cardiac stress reactions and perseverance: Diminished reactivity is associated with study non-completion

Cardiovascular reactivity to acute psychological stress is associated with generalized self-efficacy and self-efficacy outcomes during adventure challenges

Outdoor adventure challenges are commonly used to enhance self-efficacy, but the physiological mechanisms involved remain unexplored. Additionally, while studies have documented the influence of self-efficacy on stress management, general self-efficacy has yet to be fully understood in the context of cardiovascular stress reactivity (CVR). This study investigated the influence of self-efficacy beliefs on CVR during acute psychological stress tasks. Additionally, it explored whether CVR serves as a novel mechanism underlying the outcomes of outdoor adventure challenges. As part of a wider randomized controlled trial, participants (n = 55) were invited to complete a laboratory session to assess CVR to an active (paced auditory serial addition test (PASAT)) and a passive (cold pressor test (CPT)) stress task. Randomized participants (n = 33) to the experimental condition also engaged in a high ropes challenge course after the laboratory session. It was found that greater self-reported self-efficacy was associated with larger CVR during the CPT and positively associated with perceived engagement and performance during the PASAT. Secondly, participants reporting positive change in self-efficacy post-intervention were associated with greater CVR and greater CVR was associated with higher ratings of intervention engagement and perceived challenge. This study provides preliminary evidence suggesting that greater efficacy beliefs may heighten CVR to passive acute psychological stressors. Habitual stress reactivity may represent a novel mechanism involved in outdoor and adventure-based interventions. Future research should continue to explore the impact of psychological variables on stress physiology and examine CVR as a potential mechanism in adventure experiences.

Blunted cardiovascular reactivity to psychological stress and prospective health: a systematic review

Novel research demonstrates that lower or 'blunted' cardiovascular reactions to stress are associated with a range of adverse outcomes. The aim of the current review was (1) to examine the prospective outcomes predicted by blunted cardiovascular reactivity and (2) to identify a range of blunted cardiovascular reaction levels that predict these outcomes. Electronic databases were systematically searched (Medline, PsycArticles, PsycInfo, CINAHL, PubMed, Web of Science). Studies were included if they examined the prospective influence of blunted cardiovascular reactivity to psychological stress (SBP, DBP or HR) on a negative health, behavioural or psychological outcome. A total of 23 studies were included in the review. Blunted reactivity predicted (1) adverse cardiovascular health, primarily in cardiac samples (e.g., myocardial infarction, carotid atherosclerosis) and (2) outcomes associated with motivational and behavioural dysregulation in healthy samples (e.g., obesity, smoking addiction, depression). The cardiovascular reactivity threshold levels that were predictive of adverse health outcomes ranged between -3.00-12.59 bpm (14.41% to 136.59% lower than the sample mean) and -2.4-5.00 mmhg (65.99% to 133.80% lower than sample mean), for HR and DBP respectively. We posit that blunted reactions lower than, or equal to, the ranges reported here may be utilised by clinicians and researchers to identify individuals who are at increased risk of adverse cardiovascular health outcomes, as well as outcomes associated with motivational and behavioural dysregulation.

Cardiovascular reactions to acute psychological stress and academic achievement

Cardiovascular reactions to acute psychological stress have been associated with cognitive function. However, previous work has assessed cardiovascular reactions and cognitive function in the laboratory at the same time. The present study examined the association between cardiovascular reactions to acute psychological stress in the laboratory and academic performance in final year high school students. Heart rate, blood pressure, stroke volume, and cardiac output reactions to an acute psychological stress task were measured in 131 participants during their final year of high school. Performance on high school A‐levels were obtained the following year. Higher heart rate and cardiac output reactivity were associated with better A‐level performance. These associations were still statistically significant after adjusting for a wide range of potentially confounding variables. The present results are consistent with a body of literature suggesting that higher heart rate reactions to acute psychological stress are associated with better cognitive performance across a variety of domains.

The present study is the first to examine the associations between cardiovascular reactions to stress in the laboratory and academic achievement. Additionally, it is the first to examine a more comprehensive hemodynamic profile of cardiovascular reactivity (e.g., cardiac output) with cognitive function. The present results are consistent with a body of literature suggesting that higher heart rate reactions to acute psychological stress are associated with better cognitive performance across a variety of domains.

Changes in vitality in response to acute stress: an investigation of the role of anxiety and physiological reactivity

Background: Feeling alive and invigorated, or vitality, is examined within the framework of a stress paradigm. The current study investigated whether endocrine and cardiovascular responses to acute psychological stress predict declines in vitality.Methods: A sample of 90 undergraduate students completed an in-lab stressor. We measured anxiety, state vitality, cortisol levels, heart rate, and blood pressure before the task, and measured changes in state vitality, cortisol, heart rate, and blood pressure in response to the stressor. We investigated whether pre-task anxiety predicted changes in state vitality, and whether such changes were explained by physiological responses.Results: Results indicate that cognitive and somatic anxiety preceding a stressor predict changes in vitality, which is mediated by the magnitude of diastolic (95% CI [0.017, 0.517]; [0.006, 0.454]) and systolic (95% CI [0.038, 0.705]) blood pressure responses to the task. Cortisol reactivity was associated with somatic anxiety (F(6, 83) = 3.34, p < .01, β = 0.401) but was not related to changes in vitality.Conclusions: Together, these results contribute to the understanding of how physiological reactivity to a stressor can deplete vitality.

Adverse childhood experiences (ACEs) relate to blunted cardiovascular and cortisol reactivity to acute laboratory stress: A systematic review and meta-analysis

Adverse childhood experiences (ACEs) are associated with poor future mental and physical health. Altered biological reactivity to mental stress may be a possible mechanism linking ACEs to poor health. However, it is not clear if ACEs relate to blunted or exaggerated stress reactivity. This meta-analysis aimed to determine whether exposure to ACEs is associated with cardiovascular and cortisol stress reactivity. A systematic review yielded 37 sources. Random-effects modelling tested the aggregate effects of 83 studies of the association between ACEs and stress reactivity. Exposure to ACEs was associated with relatively blunted cardiovascular and cortisol stress reactivity. Effect sizes did not vary as a function of sample sex or reactivity measure (e.g., heart rate, blood pressure, or cortisol). Meta-regression revealed preliminary evidence of greater blunting in samples of a younger age and samples reporting greater ACE exposure. Subgroup analyses for stress task, ACE measurement instrument, and sample race were not conducted because of a lack of between-study variability. Exposure to ACEs is associated with dysregulation of multiple components of the human stress response system.

Blunted cardiovascular reactivity may serve as an index of psychological task disengagement in the motivated performance situations

Challenge and threat models predict that once individuals become engaged with performance, their evaluations and cardiovascular response determine further outcomes. Although the role of challenge and threat in predicting performance has been extensively tested, few studies have focused on task engagement. We aimed to investigate task engagement in performance at the psychological and physiological levels. We accounted for physiological task engagement by examining blunted cardiovascular reactivity, the third possible cardiovascular response to performance, in addition to the challenge/threat responses. We expected that low psychological task engagement would be related to blunted cardiovascular reactivity during the performance. Gamers (N = 241) completed five matches of the soccer video game FIFA 19. We recorded psychological task engagement, heart rate reactivity, and the difference between goals scored and conceded. Lower psychological task engagement was related to blunted heart rate reactivity during the performance. Furthermore, poorer performance in the previous game was related to increased task engagement in the subsequent match. The findings extend existing literature by providing initial evidence that blunted cardiovascular reactivity may serve as the index of low task engagement.

Heart Rate Reactivity to Acute Psychological Stress Predicts Higher Levels of Posttraumatic Stress Disorder Symptoms During the COVID-19 Pandemic

OBJECTIVE

Increased autonomic arousal is a proposed risk factor for posttraumatic stress disorder (PTSD). Few studies have prospectively examined the association between physiological responses to acute psychological stress before a traumatic event and later PTSD symptoms. The present prospective study examined whether cardiovascular responses to an acute psychological stress task before the COVID-19 global pandemic predicted PTSD symptoms related to the ongoing pandemic.

METHODS

Participants (n = 120) were a subsample of an ongoing research study. Phase 1 consisted of a 10-minute baseline and 4-minute acute psychological stress task with blood pressure and heart rate recorded throughout. Phase 2 was initiated 2 weeks after the COVID-19 pandemic declaration. Participants completed the Impact of Event Scale-Revised (IES-R) with respect to the ongoing pandemic. Hierarchical linear regression analyses were used to examine whether cardiovascular stress reactivity predicted COVID-19 PTSD symptoms.

RESULTS

Heart rate reactivity significantly predicted IES intrusion (β = -0.208, t = -2.28, p = .025, ΔR2 = 0.041, confidence interval = -0.021 to -0.001) and IES hyperarousal (β = -0.224, t = -2.54, p = .012, ΔR2 = 0.047, confidence interval = -0.22 to - 0.003), but not IES avoidance (p = .077). These results remained statistically significant after adjustment for sex, socioeconomic status, baseline cardiovascular activity, neuroticism, race, ethnicity, body mass index, and adverse childhood experiences. There were no statistically significant associations between blood pressure and any of the Impact of Event Scale-Revised subscales (p values > .12).

CONCLUSIONS

Diminished heart rate responses (i.e., lower physiological arousal) to acute psychological stress before the COVID-19 pandemic significantly predicted reported PTSD symptoms during the crisis.

Blunted cardiovascular reactivity to acute psychological stress predicts low behavioral but not self-reported perseverance: A replication study

Emerging evidence suggests that individuals with poor behavioral perseverance show low or blunted physiological responses to acute psychological stress. For example, a recent preliminary laboratory study demonstrated that blunted responders give up sooner and take fewer attempts when endeavoring to complete an impossible puzzle, but do not self-report poor perseverance. This present research is a replication of the previous study with an increased sample size, longer recovery periods between tasks and addition of social evaluation to the cold pressor. Participants (147) completed a self-report perseverance questionnaire (Short Grit Scale) and behavioral perseverance tasks (impossible Euler puzzle and socially evaluated cold-pressor (SECPT)). The number of attempts and time spent trying to complete the unsolvable puzzle, and duration of hand submergent during the SECPT, were recorded as behavioral perseverance measures. Difference in blood pressure (BP) and pulse rate (PR) from baseline to a 10-min paced auditory serial addition task (PASAT) were computed as reactivity. As previously, reactivity did not relate to self-reported perseverance and blunted BP reactivity to the PASAT was associated with less time persevering at the unsolvable puzzle. Additionally, blunted BP and PR reactivity to the PASAT related to poorer perseverance during the SECPT. These findings, replicating the previous study, increase confidence that blunted reactivity is a physiological marker of poor behavioral perseverance. Moreover, given that self-reported perseverance does not relate to reactivity, this suggests that blunted responders are not conscious of this detriment in perseverance, but likely need additional support when persistence is critical (e.g., during behavior change).

Social support, social participation, and cardiovascular reactivity to stress in the Midlife in the United States (MIDUS) study

This study tested two hypotheses of associations between dimensions of social connectedness and cardiovascular reactivity to acute stress: (1) high social support predicts diminished cardiovascular responses to stress (i.e., the stress-buffering model of social support), and (2) diminished cardiovascular responses predict lower social participation, a form of motivated behaviour. Participants (N = 606) in the main Midlife in the United States study completed measures of social support and social participation and underwent psychophysiological stress testing. In unadjusted analyses, social support was positively, rather than inversely, associated with reactivity. Results withstood adjustment for several control variables, but not for depressive symptoms, which was associated with diminished reactivity. Further, diminished reactivity was associated with lower social participation, but not in fully adjusted models. No robust evidence was observed for either the stress-buffering model, or for an association between diminished reactivity and lower social participation. The implications for our understanding of links between social connectedness and cardiovascular reactivity are discussed.

Childhood trauma and type D personality: The endocrine and cardiovascular effects on stress reactivity

Both exaggerated and blunted cardiovascular stress reactions are associated with health problems. Moreover, early life experiences and personality traits affect stress responses. Regarding the childhood traumas and type D personality, this study aimed to compare the endocrine and cardiovascular reactions against acute laboratory stress. Results showed that the simultaneous existence of childhood traumatic experiences and type D personality leads to exaggerated stress reactivity, while each factor results in a blunted cardiovascular response. Although the cardiovascular responses are dampened in type D personality people, their endocrine reactions are exaggerated. The underlying mechanisms of blunted cardiovascular reactivity differ between childhood trauma and type D personality groups.

American Indian young adults display diminished cardiovascular and cortisol responses to acute psychological stress

American Indian adults are at an increased risk for cardiovascular disease compared with non-Hispanic white adults. Scant research exists examining the underlying physiological and psychological mechanisms associated with these risks. This study aimed to examine possible psychological and physiological stress-related mechanisms related to cardiovascular disease risk in healthy American Indian and non-Hispanic white adults. Forty American Indian (60% female, Mean age = 19.93, SD = 2.08 years) and 45 non-Hispanic white (70% female, Mean age = 20.18, SD = 2.22 years) participants attended an in-person laboratory session. Salivary cortisol and cardiovascular activity were measured before (baseline), during, and after exposure to a 10-minute mental arithmetic task. Compared to non-Hispanic white participants, American Indian had diminished salivary cortisol (p < .001), blood pressure (p's < .001), and heart rate (p = .041) responses to acute psychological stress. These effects could not be accounted for by differences in task performance or self-reported engagement. Previous research has shown that exaggerated responses to stress are associated with increased risk of cardiovascular disease. However, diminished responses to stress are associated with early childhood stress and future adverse behaviors (e.g., addiction, obesity). Diminished reactivity may influence behaviors that can impact future development of cardiovascular disease in American Indian populations.

Establishing the validity of a novel passive stress task

Laboratory tasks used to elicit a cardiovascular stress response in the laboratory can involve either active or passive coping. However, in previous work, passive stress tasks often incorporate a distinct physical stress element, such as the handgrip or cold pressor task, meaning observed changes in cardiovascular parameters may be the result of the physical element of the stressor rather than truly reflecting psychological stress. The present study aimed to establish the validity of a psychological passive stressor; one more analogous to active tasks than those previously employed in laboratory studies. Twenty-six young, healthy adults completed a speech task in the laboratory following a resting baseline period. Twelve months later, they were invited back to the laboratory and watched the video recording of their speech. Analyses confirmed that while both tasks elicited significant SBP and DBP change (all ps < .001), only the active task was associated with HR and CO reactivity (both ps < .001), while only the passive task was associated with TPR reactivity (p = .028). Furthermore, the passive stressor was associated with a mixed hemodynamic profile, whereas the active stressor was associated with a clear myocardial profile. This study confirms that watching a video recording of oneself complete a speech task is associated with a more vascular response profile, a response associated with passive coping contexts.

Cerebrovascular regulation is not blunted during mental stress

NEW FINDINGS

What is the central question of the study? What are the effects of acute mental stress on the mechanisms regulating cerebral blood flow? What is the main finding and its importance? The major new findings are as follows: (i) high mental stress and hypercapnia had an interactive effect on mean middle cerebral artery blood velocity; (ii) high mental stress altered the regulation of cerebral blood flow; (iii) the increased cerebrovascular hypercapnic reactivity was not driven by changes in mean arterial pressure alone; and (iv) this increased perfusion with mental stress appeared not to be justified functionally by an increase in oxygen demand (as determined by near-infrared spectroscopy-derived measures).

ABSTRACT

In this study, we examined the effects of acute mental stress on cerebrovascular function. Sixteen participants (aged 23 ± 4 years; five female) were exposed to low and high mental stress using simple arithmetic (counting backwards from 1000) and more complex arithmetic (serial subtraction of 13 from a rapidly changing four-digit number), respectively. During consecutive conditions of baseline, low stress and high stress, end-tidal partial pressure of CO₂ ( P ET , C O 2 ) was recorded at normocapnia (37 ± 3 mmHg) and clamped at two elevated levels (P < 0.01): 41 ± 1 and 46 ± 1 mmHg. Mean right middle cerebral artery blood velocity (MCAv_mean ; transcranial Doppler ultrasound), right prefrontal cortex haemodynamics (near-infrared spectroscopy) and mean arterial blood pressure (MAP; finger photoplethysmography) were measured continuously. Cerebrovascular hypercapnic reactivity (ΔMCAv_mean /Δ P ET , C O 2 ), cerebrovascular conductance (CVC; MCAv_mean /MAP), CVC CO₂ reactivity (ΔCVC/Δ P ET , C O 2 ) and total peripheral resistance (MAP/cardiac output) were calculated. Acute high mental stress increased MCAv_mean by 7 ± 7%, and more so at higher P ET , C O 2 (32 ± 10%; interaction, P = 0.03), illustrating increased sensitivity to CO₂ (i.e. its major regulator). High mental stress also increased MAP (17 ± 9%; P ≤ 0.01), coinciding with increased near-infrared spectroscopy-derived prefrontal haemoglobin volume and saturation measures. High mental stress elevated both cerebrovascular hypercapnic and conductance reactivities (main effect of stress, P ≤ 0.04). These findings indicate that the cerebrovascular response to acute high mental stress results in a coordinated regulation between multiple processes.

Ventromedial prefrontal cortex connectivity during and after psychological stress in women

The ventromedial prefrontal cortex (vmPFC) integrates sensory, affective, memory-related, and social information from diverse brain systems to coordinate behavioral and peripheral physiological responses according to contextual demands that are appraised as stressful. However, the functionality of the vmPFC during stressful experiences is not fully understood. Among 40 female participants, the present study evaluated (a) functional connectivity of the vmPFC during exposure to and recovery following an acute psychological stressor, (b) associations among vmPFC functional connectivity, heart rate, and subjective reports of stress across individuals, and (c) whether patterns of vmPFC functional connectivity were associated with distributed brain networks. Results showed that psychological stress increased vmPFC functional connectivity with individual brain areas implicated in stressor processing (e.g., insula, amygdala, anterior cingulate cortex) and decreased connectivity with the posterior cingulate cortex and thalamus. There were no statistical differences in vmPFC connectivity to individual brain areas during recovery, as compared with baseline. Spatial similarity analyses revealed stressor-evoked increased connectivity of the vmPFC with the so-called dorsal attention, ventral attention, and frontoparietal networks, as well as decreased connectivity with the default mode network. During recovery, vmPFC connectivity increased with the frontoparietal network. Finally, individual differences in heart rate and perceived stress were associated with vmPFC connectivity to the ventral attention, frontoparietal, and default mode networks. Psychological stress appears to alter network-level functional connectivity of the vmPFC in a manner that further relates to individual differences in stressor-evoked cardiovascular and affective reactivity.

Diminished cardiovascular stress reactivity is associated with lower levels of social participation

Diminished cardiac reactions to acute psychological stress are associated with adverse behavioral and health-relevant outcomes. It has been proposed that diminished cardiac reactivity may be a marker for deficits in motivational functioning both at the biological and behavioral levels. Social participation reflects the frequency with which individuals participate in social events and has motivational components. As such, it is a distinct construct from other constructs such as social integration, which measures the number of social roles an individual has. Additionally, lower levels of social participation and diminished reactivity have been associated with similar adverse health outcomes. Therefore, it is possible that diminished cardiac reactivity is associated with lower levels of social participation. We aimed to examine whether diminished cardiovascular reactivity in response to an acute lab stressor was associated with reported social participation. The analyses were conducted using publicly available data from the Pittsburgh Cold Study 3 (PCS3). The PCS3 was a prospective viral-challenge study, which included participants completing an in-lab social evaluative stressor (N = 202, Age = M = 29.71, SD = 10.66) and measuring cardiovascular responses at baseline and in response to the stressor. Separate regression analyses for each cardiovascular variable (SBP, DBP, MAP, and HR) demonstrated that lower cardiovascular reactivity was associated with less social participation. These associations were still evident following adjustment for respective baseline cardiovascular levels, age, sex, race, depressive symptomology, body mass index, socioeconomic status, smoking status, and levels of social integration (R2 changes: ≥ 0.017; ps ≤ 0.02) The findings provide initial evidence that blunted cardiac reactivity may be a precursor to low levels of social participation.

Glutamate Within the Marmoset Anterior Hippocampus Interacts with Area 25 to Regulate the Behavioral and Cardiovascular Correlates of High-Trait Anxiety

High-trait anxiety is a risk factor for the development of affective disorders and has been associated with decreased cardiovascular and behavioral responsivity to acute stressors in humans that may increase the risk of developing cardiovascular disease. Although human neuroimaging studies of high-trait anxiety reveals dysregulation in primate cingulate areas 25 and 32 and the anterior hippocampus (aHipp) and rodent studies reveal the importance of aHipp glutamatergic hypofunction, the causal involvement of aHipp glutamate and its interaction with these areas in the primate brain is unknown. Accordingly, we correlated marmoset trait anxiety scores to their postmortem aHipp glutamate levels and showed that low glutamate in the right aHipp is associated with high-trait anxiety in marmosets. Moreover, pharmacologically increasing aHipp glutamate reduced anxiety levels in highly anxious marmosets in two uncertainty-based tests of anxiety: exposure to a human intruder with uncertain intent and unpredictable loud noise. In the human intruder test, increasing aHipp glutamate decreased anxiety by increasing approach to the intruder. In the unpredictable threat test, animals showed blunted behavioral and cardiovascular responsivity after control infusions, which was normalized by increasing aHipp glutamate. However, this aHipp-mediated anxiolytic effect was blocked by simultaneous pharmacological inactivation of area 25, but not area 32, areas which when inactivated independently reduced and had no effect on anxiety, respectively. These findings provide causal evidence in male and female primates that aHipp glutamatergic hypofunction and its regulation by area 25 contribute to the behavioral and cardiovascular symptoms of endogenous high-trait anxiety.SIGNIFICANCE STATEMENT High-trait anxiety predisposes sufferers to the development of anxiety and depression. Although neuroimaging of these disorders and rodent modeling implicate dysregulation in hippocampal glutamate and the subgenual/perigenual cingulate cortices (areas 25/32), the causal involvement of these structures in endogenous high-trait anxiety and their interaction are unknown. Here, we demonstrate that increased trait anxiety in marmoset monkeys correlates with reduced hippocampal glutamate and that increasing hippocampal glutamate release in high-trait-anxious monkeys normalizes the aberrant behavioral and cardiovascular responsivity to potential threats. This normalization was blocked by simultaneous inactivation of area 25, but not area 32. These findings provide casual evidence in primates that hippocampal glutamatergic hypofunction regulates endogenous high-trait anxiety and the hippocampal-area 25 circuit is a potential therapeutic target.

Increased stressor-evoked cardiovascular reactivity is associated with reduced amygdala and hippocampus volume

Exaggerated cardiovascular reactivity to acute psychological stress is associated with an increased risk of developing cardiovascular disease. The amygdala and hippocampus have been implicated in centrally mediating stressor-evoked cardiovascular reactivity. However, little is known about the associations of amygdala and hippocampus morphology with stressor-evoked cardiovascular reactivity. Forty (M_age = 19.05, SD = 0.22 years) healthy young women completed two separate testing sessions. Session 1 assessed multiple parameters of cardiovascular physiology at rest and during a validated psychological stress task (Paced Auditory Serial Addition Test), using electrocardiography, Doppler echocardiography, and blood pressure monitoring. In Session 2, 1 year later, structural MRI was conducted. Brain structural volumes were computed using automated segmentation methods. Regression analyses, following Benjamini-Hochberg correction, showed that greater heart rate and cardiac output reactivity were associated with reduced amygdala and hippocampus gray matter volume. Systolic blood pressure reactivity was associated with reduced hippocampus volume. In contrast, no associations between diastolic blood pressure, mean arterial blood pressure, stroke volume, or total peripheral resistance reactivity with amygdala or hippocampus volumes were apparent. Comparison analyses examining insula volume found no significant associations. Some indicators of greater stressor-evoked cardiovascular reactivity associate with reduced amygdala and hippocampus gray matter volume, but the mechanisms of this association warrant further study.

The behavioural, cognitive, and neural corollaries of blunted cardiovascular and cortisol reactions to acute psychological stress

Recent research shows that blunted cardiovascular and cortisol reactions to acute psychological stress are associated with adverse behavioural and health outcomes: depression, obesity, bulimia, and addictions. These outcomes may reflect suboptimal functioning of the brain's fronto-limbic systems that are needed to regulate motivated behaviour in the face of challenge. In support of this, brain imaging data demonstrate fronto-limbic hypoactivation during acute stress exposure. Those demonstrating blunted reactions also show impairments of motivation, including lower cognitive ability, more rapid cognitive decline, and poorer performance on motivation-dependent tests of lung function. Persons exhibiting blunted stress reactivity display well established temperament characteristics, including neuroticism and impulsivity, characteristic of various behavioural disorders. Notably, the outcomes related to blunted stress reactivity are similar to those that define Reward Deficiency Syndrome. Accordingly, some individuals may be characterised by a broad failure in cardiovascular and cortisol responding to both stress and reward, reflecting fronto-limbic dysregulation. Finally, we proffer a model of blunted stress reactivity, its antecedents and sequelae, and identify future research priorities.