To be Black in America is to literally feel greater pain than non-Hispanic white people and Latinxs do — at least if the pain is being inflicted by a white man wearing a white coat, if it’s happening in a lab, if it follows years of racial discrimination, and if the findings of a sobering study reported on Monday are correct.
Despite the persistence of the slavery-era myth that African Americans are less sensitive to pain than people of other backgrounds (as a large fraction of white laypeople, medical students, and hospital residents in a 2016 study believed), the science is unambiguous. African Americans, and in some studies Latinxs, report more pain from the identical stimulus (being touched with something very hot, for instance) than non-Hispanic white people. Yet somewhat surprisingly, when it seems that every mental and emotional experience has been analyzed with brain imaging, the neurobiological mechanisms for that heightened pain sensitivity have been unclear.
Hoping to remedy that, neuroscientist Elizabeth Losin of the University of Miami set out to examine brain activity when people of different ethnic backgrounds experienced the identical pain-inducing stimulus. She persisted for eight years, through funding denials (grant reviewers at the National Institutes of Health said she’d never be able to find enough Black participants around Denver), journal rejections, and a 2,000-mile move (she started the research at the University of Colorado).
“It’s been an extremely long labor of love,” she said. “But I think it’s important that the findings get out there.”
Losin and co-author Tor Wager of Dartmouth College believe their results, if replicated by others, have implications for clinical care. Doctors have historically undertreated pain in their Black patients, and often dismiss the pain of sickle cell disease patients as exaggerated or even faked. “That’s a striking contrast to what our studies show,” Wager said: “that African Americans are more sensitive to pain, and that it correlates with experiences of discrimination.”
Their findings, published in Nature Human Behaviour, start with how the participants Losin recruited — 28 African Americans, 30 Latinxs, and 30 non-Hispanic white people, all from around Denver — responded to having four spots on their left forearm touched with a device, called a thermode, heated to about 118 degrees F. (Dice-sized thermodes, heated to a precise temperature, are labs’ go-to pain sources.)
Using fMRI to scan the volunteers’ brains, the researchers saw that a circuit called the neurologic pain signature — which neuroscientist Wager found reflects the most basic aspects of pain perception — responded the same way in everyone.
Despite that, African Americans rated their pain roughly 5 points more intense, and 9 points more “unpleasant,” on a scale of 1 to 100. The more discrimination the African Americans reported having experienced in their lives, the more intensely they felt pain from the same amount of heat.
Also more intense, fMRI showed, was activity in a brain circuit that interprets non-physical aspects of pain and thereby influences pain perception.
Centered in the prefrontal cortex (site of higher-order thinking such as judgment and comprehension) and the striatum (whose many roles include assigning value to experiences), this circuit seems to be responsible for expecting pain to end (or not), feeling anxious about it, and feeling pain can or can’t be controlled. Previous research has found that activity in this circuit rises and falls not with objective attributes of pain but with these subjective ones, such as when people with chronic pain despair that their suffering will never end. And that intensifies pain.
In the African Americans in the new study, but not in other participants, this prefrontal-striatum circuit became increasingly active as the thermode’s temperature rose. Activity was also higher the more discrimination participants reported experiencing in their lives, and the less they said they trusted the experimenter, a white 30-something male.
Brain imaging studies have become notorious for results that can’t be reproduced by other labs, so these findings must be considered preliminary. Speaking about fMRI studies in general and not the pain research, neuroscientist Ahmad Hariri of Duke University cautioned that studies with only a few dozen people tend not to hold up; in a study accepted for publication, he and colleagues found that only about 20% do.
Wager said the greater pain that African Americans feel from the identical physical experience, whether painful heat or a broken bone, stems from brain circuits that interpret pain, what he called “a new [pain-related] hot spot” that assesses whether the pain will last, whether anything can be done, and whether anyone cares.
That same circuit can soothe pain, other research has found, such as when the mere belief that it is being treated can have that effect absent any actual treatment — the placebo effect.
But other beliefs and expectations, the new study shows, can do the opposite, making the same heat feel more painful, just as they make chronic pain feel worse. Negative experiences with people in white lab coats, doctors and nurses, and white men in general might trigger the same sort of anxiety as chronic pain, intensifying activity in the pain-interpreting circuits. (Multiple studies have documented high levels of cortisol and other stress hormones in people who are targets of discrimination.)
Such findings fuel the debate about whether patients are treated more compassionately and more competently by doctors of their own ethnicity. Some studies find that African American patients report less pain, both chronic and acute, when treated by African American doctors. In a soon-to-be-published study, when Losin ran the same experiment with an African American man applying the thermode, African American participants rated their pain as no greater than white people and Latinxs did.