Personality traits might do more than help you win a popularity contest. According to new University of Michigan-led neuroscience research, co-authored by University of Maryland (UM) School of Dentistry Dean Christian S. Stohler, DMD, DrMedDent, such traits also might make you more likely to get pain relief from a placebo - a fake medicine.
"This work fits into the bigger picture regarding the degree to which our individual response to a stress factor is imprinted in our personality. The release of stress-relieving neurotransmitters, such as opiates in our brain, triggered by the application of the stress explain much of the individual variance in the response to treatment," says Stohler.
In short, if you're more of an angry, hostile type, they find, a placebo won't do much for you.
For the first time, the new findings link specific, established personality traits with an individual's susceptibility to the placebo effect from a sham medicine for pain. The researchers showed a significant link between certain personality traits and how much relief people said they felt when given the placebo - as well as the level of a specific chemical that their brains released.
The work, published online today in the journal Neuropsychopharmacology, was done by a team of researchers at the University of Michigan, the University of North Carolina, and the University of Maryland.
The results build on nearly a decade's worth of work on the placebo effect by the team led by Jon-Kar Zubieta, MD, PhD, the Phil Jenkins Professor of Depression in the University of Michigan Department of Psychiatry. Stohler is a nationally recognized contributor to pain research and often collaborates with colleagues at the University of Michigan, where he served as director of research before coming to the UM School of Dentistry as dean in January 2003.
The findings show that about one-quarter of placebo response was explained by the personality traits of resiliency, straightforwardness, altruism, or anger/hostility, as measured on standardized tests. Other personality traits didn't appear to be linked to placebo response. The new results come from a few dozen healthy volunteers, so the experiment must be repeated in larger, more diverse groups to be confirmed.
If confirmed, the findings could help researchers who study new drugs and other treatments - a field where placebo responses can muddy the results and make it unclear whether the real therapy is working. Perhaps someday researchers will be able to adjust their results to account for the individual placebo responses of volunteers in their clinical trials. Zubieta notes that the new findings came from a study involving pain, but that they also may apply to how personality influences a person's response to other stress-inducing circumstances.
"We started this study not just looking at measures that might seem more obviously related to placebo responses, such as maybe impulsivity, or reward-seeking, but explored potential associations broadly without a particular hypothesis," he explains. "We ended up finding that their greatest influence came from a series of factors related to individual resiliency, the capacity to withstand and overcome stressors and difficult situations. People with those factors had the greatest ability to take environmental information - the placebo - and convert it to a change in biology."
He notes that the findings may even have implications for the doctor-patient relationship - for instance, patients who have certain personality traits and placebo-response tendencies may also be more likely to partner with their doctors on their care, and discuss frankly any concerns they have about their response to treatment.
The researchers conducted the study among nearly 50 healthy volunteers, both male and female, between the ages of 19 and 38. They gave each person a battery of standard psychological tests that help identify the strongest personality traits an individual has, and then had them lie down in a brain scanner called a positron emission tomography or PET machine.
They told the volunteers that they were going to experience pain from saltwater injected into their jaw muscle, and that a painkiller - actually, a placebo - would be injected at certain times. They asked patients to rate how much relief they expected to get before the experiment began. Then, during the 20-minute period when volunteers received saltwater and/or "painkiller," they asked them repeatedly to say how effective they thought the painkiller was.
Meanwhile, the PET scanner made images of volunteers' brains, allowing the researchers to see how much of the natural painkillers, called endogenous opioids, were released in certain areas of each person's brain under painful or "painkiller" conditions. They also drew blood from some of the patients during the experiment, and measured levels of a stress-induced chemical called cortisol.
After the tests, the researchers performed sophisticated statistical analysis to determine how personality traits influenced pain ratings, brain chemical response, and cortisol levels. Although the cortisol levels did not seem to be influenced by personality traits and the placebo effect, the endogenous opioid activation elicited by the placebo, as well as patient-rated pain intensity levels, were.
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