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Pain in a Social Context

Symposium at 2018 IASP World Congress on Pain in Boston highlighted how social interactions affect pain perception in rodents and people

by Dara Bree


28 February 2019


PRF News

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Symposium at 2018 IASP World Congress on Pain in Boston highlighted how social interactions affect pain perception in rodents and people

Pain researchers are increasingly turning their attention to the social component of the biopsychosocial model of pain. At the 2018 IASP World Congress on Pain in Boston, in a symposium titled “Pain in a Social Context,” several speakers focused on the role of social factors in the experience of pain in humans and animals.

 

Hugo Leite-Almeida, University of Minho, Braga, Portugal, began by discussing his lab’s work on how chronic pain affects multiple behavioral dimensions in rodents, particularly social interactions.

 

A growing body of evidence suggests that chronic pain can profoundly influence social behavior in rodents (Martin et al. 2014). Leite-Almeida presented ongoing studies investigating the social interactions of rats that had undergone spared nerve injury (SNI), a model of neuropathic pain. Male rats not only displayed sensitivity to mechanical stimulation, a typical behavior following SNI, but also exhibited a substantial decrease in the amount of social interactions with both familiar and unfamiliar males, which persisted for up to two months. These pain-induced deficits in social interaction appeared to be independent of sex, as female SNI rats also displayed them.

 

Leite-Almeida went on to demonstrate that gabapentin, a commonly used analgesic for neuropathic pain, diminished the social deficits resulting from pain, in both males and females. The same was true for oxytocin, a hormone involved in social interaction in mammals. While oxytocin only transiently decreased mechanical hypersensitivity in SNI rats, it robustly restored social behaviors in both males and females to a level similar to that of sham animals.

 

Together, the findings suggest that chronic pain negatively influences social behavior in rats and that investigating social interactions can provide complementary information to the commonly employed sensory readouts. Treating the pain in these animals also appears to improve impairments in social behavior. But, as the oxytocin findings demonstrate, substantial pain relief may not be necessary to alleviate those deficits in the SNI model.

 

Jeffrey Mogil, McGill University, Montreal, Canada, continued on the theme of social behavior in rodents by reminding the audience that “mice do indeed have a social life, although it’s not as good as yours I understand.”

 

Discussing previously published work from his lab, Mogil described experiments where two mice observed one another after receiving a painful injection of acetic acid (Langford et al., 2006). Acetic acid causes writhing in mice, but Mogil and colleagues observed that the animals displayed even more writhing behavior when observing another mouse in pain, compared to when they were on their own. However, this was only true for mice that observed their cage mates in pain and not strangers. The study provided the first evidence of emotional contagion, in this case empathy, in rodents.

 

Why don’t mice show empathy to strangers? Mogil believes it is because strangers are fundamentally stressful and highlighted previously published data to that effect, showing increased levels of the stress hormone corticosterone in mice that were confined with strangers (Martin et al., 2015). Blocking the synthesis of corticosterone produced empathic behaviors in mice that were strangers to one another, suggesting that the stress response can block empathy in mice. With an eye to translational aspects of this work, Mogil finished by mentioning ongoing experiments his lab is conducting in humans to investigate emotional contagion and empathy during pain.

 

Moving to human social interactions in the context of pain, Tine Vervoort, Ghent University, Belgium, presented findings on perceived injustice on the part of parents about their child’s pain, and how these perceptions shape how parents will care for their child in pain.

 

For parents, seeing their child in pain is often viewed as an imminent threat that something may be seriously wrong. This natural response by parents is described as a catastrophic appraisal of their child’s pain and is commonly reported among parents of children with chronic pain.

 

Vervoort argued that this inherent catastrophic appraisal by parents is not the only way that they appraise their child’s pain. Children who suffer from chronic pain often experience severe disruptions to their normal activities such as attending school, playing with friends, and interacting with family members. Moreover, the treatment that children receive for pain is often suboptimal. All of this can produce feelings of injustice in parents, manifested by sentiments like, “It is not fair that my child is enduring this.” Furthermore, parenting a child suffering from chronic pain can bring substantial challenges, losses, and interference with goals for parents themselves, engendering sentiments like, “It’s not fair that I as a parent am enduring this.” Such appraisals highlight how parents believe that their child with chronic pain is being deprived of a normal life, and also how their normal roles as parents are disrupted.

 

A recent study has shown that high perceived injustice by parents with regard to their child’s pain contributes to more negative outcomes for the child, including greater pain intensity and functional disability (Miller et al., 2018). Vervoort and colleagues, however, were also interested in addressing parental self-appraisal of injustice, defined as how unfair their child’s pain was for them as a parent. During her talk, Vervoort described a recently completed, unpublished study investigating self- and child-oriented injustice appraisals in parents of healthy children and parents of children with chronic pain. For parents of healthy children, the worse the fathers' (but not the mothers') self-oriented injustice appraisals about their child’s pain, the worse the social functioning of the child. Conversely, for parents of children with chronic pain, child-oriented and not self-oriented injustice appraisals correlated negatively with numerous aspects of child functioning, including not only social functioning, but also physical and emotional functioning.

 

Vervoort also commented on the assessment of parental injustice appraisals, which is based upon the parental version of the Injustice Experience Questionnaire (IEQ) and may not capture the full story. So, alongside international collaborators, Vervoort set up focus groups of mothers of children with chronic pain. Asking them questions concerning the extent to which they felt life was unfair for them or their child, Vervoort and colleagues characterized three primary elements not necessarily captured by the parental version of the IEQ. These included a social comparison where parents felt they received unequal judgment/treatment compared to parents whose children don’t have chronic pain or who have other conditions, such as cancer, that are perceived as more serious and which often include a greater level of understanding and sympathy by others. Parents also reported a perceived invalidation of the child’s condition by others and reported feeling blamed for causing or imagining their child’s pain. Lastly, a battle for their child’s quality of life was also highlighted by parents, including fighting with health care providers over diagnosis or treatment, and with schools for more understanding and additional resources to help the child’s education.

 

In sum, Vervoort highlighted the need to further study the nature of parental injustice appraisals and the mechanisms of action explaining their impact on child pain-related outcomes.

 

Rounding out the session was Irit Weissman-Fogel, University of Haifa, Israel, who returned to the theme of empathy, this time in humans, and discussed the analgesic effects of affective/social touch, in this case hand-holding. For Weissman-Fogel, what raised the question of whether and how touch can reduce pain was when a colleague reached out to hold the hand of his wife during the birth of their child. He noticed that his wife felt much less pain when he held her hand. Social touch in general has been demonstrated to improve overall emotional well-being in people, but the term can encompass a variety of physical contact and is often dependent on the identity of the toucher and his or her ability to be empathic.

 

In the context of pain, empathy has been defined as the sense of knowing the experience of another person suffering from pain and has cognitive, affective, and behavioral components. Brain regions such as the anterior cingulate and insular cortices are involved in coding empathy for pain.

 

“It has been suggested that our empathic ability will not only shape the way we perceive the pain of others but will also influence the way we react to it,” Weissman-Fogel told the audience.

 

In previously published work, Weissman-Fogel and colleagues recruited couples to participate in a study where the female was subjected to a painful stimulus in the absence of her partner, in the presence of her partner but with no touch, in the presence of her partner with hand-holding, or in the presence of a stranger with hand-holding (Goldstein et al., 2016). Partner hand-holding caused a reduction in pain scores, more so than in the presence of the partner with no social touch, in the absence of the partner, and in the presence of a stranger with social touch. Higher empathy levels in partner hand-holding males were related to a greater level of pain reduction reported by females compared to partners present with no social touch. A later study showed that, during hand-holding, higher empathy levels of the male partner were accompanied by greater cardio-respiratory synchronization along with greater pain reduction experienced by the female (Goldstein et al., 2017).

 

In unpublished work, Weissman-Fogel’s group placed either the toucher or the person in pain (the target) in an fMRI scanner on separate occasions. There was a correlation between activity in the insular cortex of the target and activity in the anterior cingulate cortex ACC of the toucher. Specifically, higher activity in the toucher’s ACC was related to reduced activity in the target’s insular cortex, which occurred alongside pain reduction during social touch, providing a possible neural signature underlying social analgesic touch. Simple tactile stimulation from an object didn’t appear to explain the phenomenon of analgesic touch, explained Weissman-Fogel, as subjects were also asked to rate their pain while holding a baseball and did not report any reduction in pain levels.

 

In summary, the social component of the pain experience is highly relevant to both animals and humans, and adaptive social behaviors in the face of pain can have profound effects on coping with and modulating pain. It’s time to increase recognition and understanding of the “social” in the biopsychosocial model of pain.

 

Dara Bree is a postdoctoral fellow at Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, US.

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