The Science of What Makes Pain So Personal
The measurement of pain has long plagued doctors. It seems like an intractable problem: Pain is subjective, felt only by the sufferer, making it immensely difficult to communicate to those on the outside. For decades, scientists hypothesized the physical sensation was closely tied to gender, personal willpower, and ethnic or racial background. But for neurologist Asenath Petrie, those explanations left something to be desired.
In her 1967 book Individuality in Pain and Suffering, Petrie declared, “Our research suggests...that these differences may, in part, be due to ways of experiencing the environment that vary according to the perceptual modulation of the individual” (98, emphasis in original). In other words, Petrie surmised, something more innate than culture and willpower determines how a person feels pain. Perhaps it has something to do with unique, individual bodies.
Trained as a psychologist, and the daughter of a British rabbi, Petrie taught biology at a Jewish school during the interwar period, then worked in the Neurosis Center for Allied Forces in London during World War II. After the war, she visited the Bergen-Belsen concentration camp, and helped create a program to help those survivors, while also studying to complete her doctorate in neuropathology. Those experiences formed the basis of her career in medicine, and attuned her to the kinds of emotional pain that came from being a Jewish woman in a patriarchal, anti-Semitic world.
“In other words, Petrie surmised, something more innate than culture and willpower determines how a person feels pain. Perhaps it has something to do with unique, individual bodies.”
Despite those obstacles, Petrie thrived. In 1951, she traveled to the United States with a Fulbright Grant. She continued her research with funding from the Rockefeller Foundation, the National Institutes of Health, and the Lasker Fund. Her work on neurology and psychology gained enough popular recognition that she received an invitation to the White House, appeared on the Today show, and joined the staff at Harvard in 1957.
In her investigation of pain, Petrie focused first on how patients perceived their environment, rather than simply analyzing their suffering. Participants were blindfolded, then given an object to measure with their hands. Afterwards, their fingers were stimulated continuously for a set amount of time, then they were asked to replicate the measurement they’d previously felt. The people Petrie studied were assigned to three main categories: the reducers, the moderates, and the augmenters. Those classified as reducers consistently indicated a smaller sized object than they were presented with after the period of stimulation. As their names suggests, moderates gave approximately correct measurements, while augmenters increased the size of the object.
These categories developed by Petrie also consistently corresponded with how the individuals experienced pain. Reducers felt less of it, augmenters felt much more. In fact, augmenters seemed so sensitive to pain and other sensations that they felt discomfort from bright lights and loud noises that didn’t bother members of the other groups.
This approach was staggeringly different than the studies conducted by other doctors and psychologists of the era. Usually, measuring pain required inflicting it. The earliest dolorimeter, developed in 1940, used light and heat to gauge the pain a subject experienced when being burned. Researchers also applied pressure until it reached a painful level, or used a copper wire fixed around a tooth to deliver electric shocks.
Other types of testing manipulated subjects’ biases. In one 1950s experiment, doctors at McGill University told Jewish women that, compared to non-Jews, they had an inferior pain tolerance. After receiving that information, the women displayed much higher pain tolerances than had previously been recorded. The same results were produced when Christians were told they tolerated less pain than Jews. In both cases, pain tolerance meant status.
Petrie’s work, on the other hand, eschewed inflicting pain and mostly ignored categories like gender, race, religion, and ethnicity. She hypothesized that the experience of pain came down to something more intrinsic than any of those categories. It came from the individual’s nervous system, something beyond their control—and therefore beyond judgment.
Despite Petrie’s previous scientific and popular acclaim, other scientists opined that Petrie’s hypothesis of augmenters and reducers was insufficiently supported by evidence. “This book fails to redeem its promise,” wrote the prominent Harvard psychologist Philip Holzman in a devastating review in the prestigious journal Science. In his review for the American Journal of Psychology, the researcher B. Berthold Wolff also challenged Petrie’s work: “As yet the author’s hypothesis is based on previously published preliminary and largely uncontrolled experimental evidence, usually involving … anecdotal information.”
Although Petrie received some positive reviews, the book was her last large-scale scientific work, and other researchers struggled to replicate the results she’d found. Whether that was a result of the work itself, or the fact that she was a woman in a field dominated by men—a field that often dismissed women’s complaints of pain altogether—is hard to say.
But 30 years after Individuality in Pain and Suffering, the ideas behind Petrie’s work found their way into neurological science again. The process of amplifying experiences had a new name: sensory-processing sensitivity. Augmenters found a new identity as “highly sensitive people,” or HSPs.
The new trait was proposed by clinical psychologist Elaine Aron, who stumbled upon it while attempting to quantify what researchers meant when they indicated that patients displayed “sensitivity.” The term seemed so amorphous, applied in so many scenarios, and so fraught with judgment, that it was hardly useful in a research setting. Yet when Aron investigated further, she discovered that sensitivity could be pinned down to several concrete traits: ease of excitation (being easily overwhelmed by environmental stimuli like noise and light), low sensory threshold (responding more quickly to things like caffeine, medications, or pain), and aesthetic sensitivity (a heightened awareness of detail). In studies repeated across populations from different cultures and backgrounds, Aron and others found that 15 to 20 percent of people consistently fell into the HSP category.
Biologists have even applied the trait to evolutionary studies to explain why it might have developed in so many populations. They concluded that it is helpful to have a minority particularly sensitive to the environment, because those individuals can warn others of perceived threats. But the trait is also negative frequency dependent, meaning that it has high costs. If everyone experienced the world this acutely, no one would ever take risks or make new discoveries. The pain of living might become too great across the entire population.
“If everyone experienced the world this acutely, no one would ever take risks or make new discoveries. The pain of living might become too great across the entire population.”
While studying this new trait and hearing from people who struggled with it, Aron realized that she, too, was an HSP, and that it could be a burden. “Certainly the world does not let up on giving us false reviews about what’s so odd, annoying, or limiting about our sensitivity,” Aron wrote as she continued to explore the subject.
But that didn’t mean the trait, which could be construed as making people more fragile, was without benefits. Sometimes a lower threshold for pain, physical and emotional, can be used to steer society in a safer, more just direction, Aron argued.
Petrie spent the latter half of her career away from science, and seems never to have engaged with Aron’s research. After moving to Israel in 1973, Petrie transitioned to the arts. She began writing poetry, which was published through 1994. She also penned an autobiographical diary, Rerooted in Jerusalem, in which she reflected on the many pains and pleasures of the Jewish experience. “A damaged eye hides its hurt,” Petrie writes in one. “That missing piece is filled in; the viewer, self-deceived, fails to see her world as incomplete.”
In this, and other poems, Petrie seems to hint at the difficulties of asking questions that don’t yet have answers, or whose answers won’t be recognized by others.
Further Reading
Joanna Burke, The Story of Pain: From Prayer to Painkillers (Oxford University Press, 2014).
Robert Gregory Boddice, ed., Pain and Emotion in Modern History (Palgrave, 2014).
Image credit: After the Pogrom, Maurycy Minkowsky, 1910 via The Jewish Museum