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These images created from data gathered
on PET scanners shows the areas of the brain where levels of natural
mu-opioid painkillers rose in healthy volunteers who received a
painful injection followed by a placebo. This response corresponded
with certain personality traits.
Credit: Zubieta laboratory,
University of Michigan
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Are you good at coping when life gets tough? Do people call you a straight-shooter? Will you help others without expecting anything in return?
Those personality traits might do more
than help you win a popularity contest. According to new University
of Michigan-led neuroscience research, those qualities also might
make you more likely to get pain relief from a placebo – a fake
medicine.
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 U-M
Medical School researchers and their colleagues at the University of
North Carolina and 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, M.D., Ph.D., the Phil Jenkins Professor of Depression in the
U-M Department of Psychiatry, a professor in the Department of
Radiology and a member of the Molecular and Behavioral Neuroscience
Institute.
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 really muddy the results and make it
unclear whether the real therapy is working. Perhaps one day
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 it may also 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 the 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 and his team, including first
author, former MBNI postdoctoral fellow and now psychiatry research
investigator Marta Peciña, M.D., Ph.D., hope to continue the
research in people with depression, and to continue to explore how
genetics as well as personality influence placebo response.
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.
How it was done:
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 salt water 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 salt water and/or
"painkiller", they asked them repeatedly to say how
effective they though 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.
In addition to Zubieta and Peciña, the
team included Hamdan Azhar, M.S. and Tingting Lu, M.S., of MBNI and
the U-M School of Public Health's Biostatistics program, MBNI
research investigator Tiffany M. Love, Ph.D., Barbara L. Fredrickson,
Ph.D. of UNC, and Christian S. Stohler, D.M.D. of U. Maryland. The
research was supported by grants from the National Institutes of
Health, including R01 AT 001415, R01 DA 016423 and R01 DA 022520, and
by the Phil F. Jenkins Foundation.
Volunteers are needed for other studies
by this team; visit www.umclinicalstudies.org and search for
Zubieta.
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