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Higher Pain Ratings in African Americans Rooted in Discrimination

Brain imaging suggests differences in pain stem from life experience, not nociceptive circuitry

by Stephani Sutherland

31 March 2020

PRF News

brain scan abstract illustration. Magnetic resonance imaging of the brain

Brain imaging suggests differences in pain stem from life experience, not nociceptive circuitry

Despite a still-common belief that African Americans feel less pain than Whites, the evidence shows that the former report more pain than the latter, both in clinical and laboratory settings. Consistent with that evidence, a new study now shows that African Americans reported greater pain than White Americans or Hispanic Americans in response to a painful heat probe. Further, the differences were traced to specific sociocultural factors rooted in discrimination, which was reflected in brain-processing differences in extra-nociceptive circuitry but not in nociceptive circuitry.


Tor Wager and first author Elizabeth Reynolds Losin carried out the research while at the University of Colorado, Boulder, US. Wager is now at Dartmouth College, Hanover, US, and Losin is at the University of Miami, Coral Gables, US.


“It’s an excellent paper, and a unique contribution, particularly in terms of its ability to incorporate the biological, the psychological, and the social perspective. Their thinking is broadband,” said Kenneth Craig, a pain researcher at the University of British Columbia, Vancouver, Canada, who was not involved in the study.


The work appeared online February 3 in Nature Human Behavior.


Demographic disparities in pain

Describing the impetus for the work, Losin said, “there’s a large literature on demographic disparities in pain. Women and minorities report more pain, but there’s not a lot of understanding about where those differences are coming from.”


While many factors could account for the disparities, Losin continued, “we thought that by digging in with brain imaging, we could shed some light on those factors.”


The study included 88 men and women; 28 were African Americans (AA), 30 were non-Hispanic White Americans (WA) and 30 were Hispanic Americans (HA). Subjects were scanned with functional magnetic resonance imaging (fMRI) while they continuously rated their pain in response to a thermal probe to the arm. The researchers quantified the “area under the curve” as a composite summary of pain ratings over the course of each heat trial.


As suggested by earlier studies, AA subjects rated their pain as more intense and more unpleasant than did WA or HA subjects. They also displayed a steeper dose-response curve for pain ratings, meaning that “for every degree increase in thermal stimulation on their arm, they had a bigger jump in how much more painful they said it was than the other two groups,” Losin explained. There were no differences in pain ratings between WA and HA subjects.


“It’s important to think of the painful experience as a very complex process,” Craig said. One limitation of the study, he noted, was that the pain responses focused primarily on sensory aspects of the experience. “I’d rather that the pain reports had differentiated sensory, affective, and possibly cognitive aspects.” Post-trial ratings included sensory and affective qualities, he added, so “the paper begins to approach the necessity of differentiating qualities,” according to Craig.


Pain ratings reflect a lasting legacy of discrimination

The findings that African Americans are more sensitive to pain than Whites stands in contrast to prevailing biases among healthcare professionals and others that the former are less sensitive to pain. For instance, a 2016 study showed that lay individuals as well as medical students and residents rated African Americans’ pain as lower than that of Whites (Hoffman et al., 2016). The bias stemmed from false beliefs about biological differences based on race, such as “black people’s skin is thicker than white people’s skin.” Half the medical trainees held such false beliefs.


“What’s particularly striking about the ethnicity and race stereotypes is that the whole literature – both experimental and clinical – on pain disparities shows exactly the opposite pattern,” Losin said. “The actual research shows that African Americans tend to report more pain, more pain unpleasantness, more pain intensity, and more pain-related disability than Whites. So there’s a sort of double disparity in that you not only have a group reporting more pain, but you have beliefs on the part of clinicians and the general public going in the opposite direction.” 


To find the root of the discrepancy, Losin identified 19 sociocultural factors that could contribute to disparities in pain ratings, including pain catastrophizing, socioeconomic status, and stressful life events. Only three of the factors were significantly different among the groups, suggesting they influenced the pain ratings. Those three factors were higher incidences of discrimination, more frequent responses to discrimination (such as reporting a complaint), and distrust of the white male experimenter in the study, who was in his 30s and wore a medical lab coat. Distrust of the experimenter, Losin said, “I suspect may be related to previous medical experiences.” Further analysis showed that subjects’ history of responding to discrimination explained the higher pain ratings.


The extra-nociceptive system

The researchers then examined fMRI images, captured while participants responded to the heat probe, to see whether brain activity patterns differed among the groups. In particular, the investigators focused on the neurologic pain signature (NPS), a brain-wide pattern of activity that Wager and colleagues previously identified as tracking nociceptive pain (Wager et al., 2013PRF related news).


“The NPS is both highly sensitive and highly specific,” Losin said. “It predicts very well what people are going to say in terms of pain rating – it follows stimulus intensity very well – but it doesn’t respond to things that share some qualities of pain but are not pain, like social rejection.”


But, in the current study, Wager said, “There were no appreciable differences between the different ethnic groups” with regard to the NPS.


However, in frontostriatal brain regions in AA participants, the researchers did find greater pain-related activity, which accounted for their higher pain ratings, than in the other groups. These regions, including the ventromedial and medial prefrontal cortex and nucleus accumbens, are associated with pain valuation and chronification – but not nociception.


“The brain systems that seem to mediate pain in African Americans especially are the ones that are increasingly showing up as important in chronic pain,” Wager told PRF. “These are systems that are really important for appraisal and meaning. And there is growing evidence for increased connectivity between these non-nociceptive regions and other nociception- and pain-related areas like the insula in people with chronic pain” (see, e.g., López-Solà et al., 2017). 


“I think it’s exceedingly important to think about these extra-nociceptive systems as features of the experience of pain,” said Craig. 


“We think that this system is related to the need to avoid and withdraw from pain – part of the suffering aspect of pain,” Wager wrote in an email to PRF. 


Experience, not biology, underlies differences in pain

The results suggest that life experience, rather than inherent biological differences, underlie the ethnic groups’ different experiences of pain, Losin said.


“There’s a common misconception that if you’re seeing differences between people that are reflected in brain activity, then those differences must be rooted in immutable aspects of our biology,” she said. “Though we see differences in the brain, those differences are correlated with measures of people’s life experiences of discrimination,” she said. “So they look like they’re probably coming from African Americans’ history of negative social experiences, and not from basic differences in pain physiology.”


“The common factor in chronic pain patients and perhaps in African Americans, at least in our sample, is these chronic experiences of stress, and the fact that they may be sensitizing certain parts of the brain to pain that are not necessarily normally tracking pain intensity,” Losin continued.


Craig agreed, adding that “pain is an incredibly powerful event that influences the brain, but certain life circumstances can be exceedingly important as well. So it’s reasonable to posit that the trauma and violence sustained by people in marginalized populations, who suffer abuse and discrimination all the time, also have an impact on brain systems. So there may be predispositions to react differently to pain in people whose brains have been shaped by those kinds of circumstances.”


Healthcare providers’ biased assessment of people’s pain leads to real-world disparities in diagnosis and treatment of pain, which have also been well documented. Losin hopes that by shedding light on the true source of differences in pain – namely discrimination – it could help correct biases and reduce disparities in care. 


Stephani Sutherland, PhD, is a neuroscientist and freelance journalist in Southern California. Follow her on Twitter @SutherlandPhD


Image credit: arkela/123RF Stock Photo.

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