Chronic non-medical prescription opioid use and empathy for pain: Does pain make the difference?

Empathic pain: Exploring the multidimensional impacts of biological and social aspects in pain

Empathic pain refers to an individual's perception, judgment, and emotional response to others' pain. This complex social cognitive ability is crucial for healthy interactions in human society. In recent years, with the development of multidisciplinary research in neuroscience, psychology and sociology, empathic pain has become a focal point of widespread attention in these fields. However, the neural mechanism underlying empathic pain remain a controversial and unresolved area. This review aims to comprehensively summarize the history, influencing factors, neural mechanisms and pharmacological interventions of empathic pain. We hope to provide a comprehensive scientific perspective on how humans perceive and respond to others' pain experiences and to provide guidance for future research directions and clinical applications. This article is part of the Special Issue on "Empathic Pain".

Endogenous opioid receptor system mediates costly altruism in the human brain

Functional neuroimaging studies suggest that a large-scale brain network transforms others' pain into its vicarious representation in the observer, potentially modulating helping behavior. However, the neuromolecular basis of individual differences in vicarious pain and helping is poorly understood. We investigated the role of the endogenous μ-opioid receptor (MOR) system in altruistic costly helping. MOR density was measured using [11C]carfentanil. In a separate fMRI experiment, participants could donate money to reduce a confederate's pain from electric shocks. Participants were generally willing to help, and brain activity was observed in amygdala, anterior insula, anterior cingulate cortex (ACC), striatum, primary motor cortex, primary somatosensory cortex and thalamus when witnessing others' pain. Haemodynamic responses were negatively associated with MOR availability in emotion circuits. However, MOR availability positively associated with the ACC and hippocampus during helping. These findings suggest that the endogenous MOR system modulates altruism in the human brain.

Substance Use-Related Alterations of Social Decision Making in a Longitudinal Cohort of Young Adults

BACKGROUND

Substance use disorders are associated with severe negative social and health-related outcomes. Evidence has accumulated that long-term substance use is associated with alterations in social interaction behavior, which likely contributes to the vicious cycle of substance use disorder. However, little is known about whether these social problems originate from contextual factors only or also from the substance use itself-in other words, if they are predisposed or substance induced.

METHODS

We studied the causation behind behavioral alterations of substance users over a 9-year period (ages 11-20 years) in an urban age cohort (N = 1002) with a high prevalence of substance use at age 20. We identified common substance use patterns using toxicological hair analysis, examined behavioral alterations with incentivized games, and used teacher assessments across different ages to determine the causes and effects that underlie substance use-related impairments in social interaction.

RESULTS

We found that opioid and stimulant users showed reduced prosocial behavior compared with nonusers, particularly in interpersonal trust and perspective taking (e.g., they were approximately 50% less likely to trust others). Our longitudinal analyses suggest a causal relationship between the nonmedical use of prescription opioids and impaired social behavior, whereas impairments among stimulant users seem to be partially predisposed. Moreover, women tended to be more severely affected by opioid use than men. However, no behavioral alterations were found among young adult cannabis or ecstasy users.

CONCLUSIONS

Highly addictive substances such as opioids can impair users' social behavior by undermining fundamental human interaction, thereby fueling a vicious cycle of substance use and social isolation.

Endocannabinoids and related lipids linked to social exclusion in individuals with chronic non-medical prescription opioid use

Opioid-related overdose deaths are still on the rise in North America, emphasizing the need to better understand the underlying neurobiological mechanisms regarding the development of opioid use disorder (OUD). Recent evidence from preclinical and clinical studies indicate that the endocannabinoid system (ECS) may play a crucial role in stress and reward, both involved in the development and maintenance of substance use disorders. Animal models demonstrate a specific crosstalk between the ECS and the endogenous opioid system. However, translational studies in humans are scarce. Here, we investigated basal plasma levels of the endocannabinoids anandamide (AEA) and 2-arachidonoyglycerol (2-AG), and eight endocannabinoid-related lipids, including oleoylethanolamide (OEA) and palmitoylethanolamide (PEA), as well as whole blood fatty acid amide hydrolase (FAAH) activity in chronic non-medical prescription opioid users (NMPOU; n = 21) compared to opioid-naïve healthy controls (n = 29) considering age, sex, and cannabis use as potential confounders. Additionally, the association of endocannabinoids and related lipids with the participants' response to experimentally induced social exclusion was examined. We found significantly elevated basal AEA, OEA, and PEA levels in NMPOU compared to controls, but no differences in FAAH activity, 2-AG, or other endocannabinoid-related lipids. Within NMPOU, higher AEA levels were associated with lower perception of social exclusion. Robust positive correlations within N-acylethanolamines (i.e., AEA, OEA, and PEA) indicate strong metabolic associations. Together with our recent findings of elevated basal 2-AG levels in dependent cocaine users, present results indicate substance-specific alterations of the ECS that may have implications in the search for novel therapeutic interventions for these populations.

Dissecting shared pain representations to understand their behavioral and clinical relevance

Accounts of shared representations posit that the experience of pain and pain empathy rely on similar neural mechanisms. Experimental research employing novel analytical and methodological approaches has made significant advances in both the identification and targeted manipulation of such shared experiences and their neural underpinnings. This revealed that painful experiences can be shared on different representational levels, from pain-specific to domain-general features, such as negative affect and its regulation. In view of direct links between such representations and social behaviors such as prosocial behavior, conditions characterized by aberrant pain processing may come along with heavy impairments in the social domain, depending on the affected representational level. This has wide potential implications in light of the high prevalence of pain-related clinical conditions, their management, and the overuse of pain medication. In this review and opinion paper, we aim to chart the path toward a better understanding of the link between shared affect and prosocial behavior.

A pill as a quick solution: association between painkiller intake, empathy, and prosocial behavior

Previous research has demonstrated a link between the administration of analgesic drugs and the reduction of empathy levels in humans. This apparent blunting effect of pain medication has been explained through shared neural mechanisms for the first-hand and the empathic experience of pain (simulation theory). Considering that analgesics are among the most consumed drugs in the world and the ability to empathize with others is fundamental to human social interactions, the aim of the present study was to investigate whether the typical day-to-day analgesic consumption rate in Austria and Germany is associated with a reduction in empathy and prosocial behavior. We therefore collected self-reports of analgesic consumption behavior as well as empathy for pain and prosocial behavior measures in an online survey (n = 940). Analyses revealed no significant association between the analgesic intake frequency and measures of empathy or prosocial behavior. However, liberal intake of analgesics (i.e. mind-set of "a pill is a quick solution") was linked to lower empathic concern and helping behavior, which may hint towards a negative effect in people who take pain medication for non-pain related issues or episodes of low pain. Nevertheless, further research is needed to investigate the effects of analgesic drugs in high frequency users.

Association between opioid use disorder and blunted heart rate variability among opioid-treated chronic pain patients

Given the severity of the ongoing opioid epidemic, it is essential to understand the mechanisms of risk for development and maintenance of opioid use disorder (OUD). The aim of the current large-scale psychophysiological investigation was to test whether patients with OUD had lower resting-state high-frequency heart rate variability (HF-HRV) than those without OUD, controlling for sociodemographic and clinical confounds. Additionally, we tested whether HF-HRV was associated with opioid craving in this population. Participants in this cross-sectional study were 490 chronic pain patients (50.4% female) treated with long-term opioid therapy. OUD diagnosis was determined by psychiatric interview. HF-HRV was measured at resting baseline. We computed the association between OUD and resting-state HF-HRV, controlling for age, gender, race, pain severity, emotional distress and opioid dose. Opioid craving was measured with visual analogue scales to assess whether HF-HRV was associated with craving. Results showed that resting HF-HRV was significantly lower for patients with OUD than for those without OUD (p < 0.001, d = 0.36), indicating deficits in autonomic flexibility. OUD diagnosis (p = 0.002) and OUD severity (p = 0.03) were associated with lower HF-HRV in regression models accounting for a range of confounders. Additionally, lower HF-HRV was significantly (but weakly) correlated with heightened opioid craving (r = -0.166, p < 0.001). Overall, findings suggest that resting-state HF-HRV may serve as a valid biomarker of addiction among people on long-term opioid therapy.

Effects of the mu-opioid receptor agonist morphine on facial mimicry and emotion recognition

Facial mimicry and emotion recognition are two socio-cognitive abilities involved in adaptive socio-emotional behavior, promoting affiliation and the establishment of social bonds. The mu-opioid receptor (MOR) system plays a key role in affiliation and social bonding. However, it remains unclear whether MORs are involved in the categorization and spontaneous mimicry of emotional facial expressions. Using a randomized, placebo-controlled, double-blind, between-subjects design, we investigated in 82 healthy female volunteers the effects of the specific MOR agonist morphine on the recognition accuracy of emotional faces (happiness, anger, fear), and on their facial mimicry (measured with electromyography). Frequentist statistics did not reveal any significant effects of drug administration on facial mimicry or emotion recognition abilities. However, post hoc Bayesian analyses provided support for an effect of morphine on facial mimicry of fearful facial expressions. Specifically, compared to placebo, morphine reduced mimicry of fear, as shown by lower activity of the frontalis muscle. Bayesian analyses also provided support for the absence of a drug effect on mimicry of happy and angry facial expressions, which were assessed with the zygomaticus major and corrugator supercilii muscles, as well as on emotion recognition accuracy. These findings suggest that MOR activity is involved in automatic facial responses to fearful stimuli, but not in their identification. Overall, the current results, together with the previously reported small effects of opioid compounds, suggest a relatively marginal role of the MOR system in emotion simulation and perception.

Resting Heart Rate Variability, Perceived Emotion Regulation, and Low-Risk Drug Use in College-Aged Adults: Gender as a Moderator

Identification of individual differences in drug use is warranted, as a history of use is associated with future drug problems. Such drug use is thought to disrupt inhibitory and motivation networks involved in emotion regulation (ER). Higher resting heart rate variability (HRV), a biomarker of effective inhibitory abilities, is associated with less substance (e.g., alcohol, opioid) use. Higher HRV is associated with lower perceived ER difficulties, and this link is stronger in women relative to men. Evidence suggests women might engage in drug use primarily to reduce stress, and men primarily to induce feelings of elation. Research has yet to examine associations among individuals' difficulties in ER, resting HRV, and a recent history of drug use; the current study explored this, in addition to how these associations might differ as a function of gender. Young and healthy college students (N = 190; 88 women) completed a 5-min baseline to assess resting HRV, followed by the 36-item difficulties in ER Scale and 10-item Drug Abuse Screening Test. Higher difficulties in ER, but not resting HRV, were associated with a greater history of "low-risk" drug use in the full sample and moderation tests confirm this link was stronger in women. Moderated-mediation results confirmed an indirect association between resting HRV and drug use, mediated by self-reported difficulties among women only. A significant association between resting HRV and Difficulties in Emotion Regulation Scale (DERS) emerged only among women without a history of drug use. These results indicate that difficulties in ER are both associated with a low-risk history of drug use and underlie an indirect link between resting HRV and drug use history in women only. Among these women with a history of drug use relative to women without, there was no link between resting HRV and self-reported difficulties in ER, suggesting a disrupted inhibitory-motivational pathway. Additional work is needed to understand the psychophysiological correlates of a history of low-risk drug use in young men. These data are in line with research suggesting gender differences in the motivation to engage in recreational drug use and ER interventions might be important in women who engage in low-risk recreational drug use.