Personality Predicts Placebo Effect
People with certain personality traits are more likely to get pain relief from a placebo, a finding that could help improve clinical trials.
By Dan Cossins | November 16, 2012
Colored areas show regions of greater mu-opioid release during placebo administration in volunteers with high levels of resilience, straightforwardness and altruism, and low levels of angry hostility. Individuals who are altruistic, resilient, and straightforward show greater activity in brain regions associated with reward and are more likely to enjoy pain relief when a placebo is administered during a painful experience, according to a study reported this week (November 15) in Neuropsychopharmacology. The findings suggest that simple personality tests could be used to improve the accuracy of clinical trials by identifying people likely to skew results with high placebo responses..
Placebos are known to have strong analgesic effects. In 2007, neuroscientist Jon-Kar Zubieta of the University of Michigan showed that such effects were associated with activity in the nucleus accumbens, a brain region involved in reward and pleasure. That suggested that placebo analgesia might occur in part because positive expectations of reward (pain relief) spike dopamine levels in the brain and stimulate the release of endogenous painkillers called mu-opioids...
To better understand how personality is associated with placebo analgesia, Zubieta and his colleagues assessed the personality traits of 47 healthy volunteers. Then they asked each volunteer to lie in a positron emission tomography (PET) scanner for the duration of a standard pain challenge. First, painless isotonic saline was injected into the jaw muscle and, 20 minutes later, a pain-inducing hypotonic injection. Volunteers were told about these two conditions but not the order in which they would occur, allowing for expectation of pain in both conditions. The conditions were then repeated for another scan session but this time the volunteers were given a placebo consisting of intravenous infusions of isotonic saline every 4 minutes, which they were told would reduce pain.
... they also found that people with certain personality traits—specifically, those who scored high on resiliency, altruism, and straightforwardness, and low on measures of “angry hostility”—were more likely to experience a placebo-induced painkilling response. Importantly, such individuals also had decreased cortisol levels and greater activation of endogenous opioid receptors in brain regions associated with reward.
“We were able to link some personality traits with analgesia response at the level of brain chemistry,” said Zubieta, as well as subjective feelings...