Don’t be fooled by some of the jargon of biomedical research: People who respond strongly to placebo medications are not dummies. A new study finds they tend to be people you would describe in much more favorable terms: straightforward, tough in the face of difficulty, and willing to lend others a hand.

Maybe the people who don’t respond well to placebos are the dummies: Angry, hostile and prone to negativity, these people seem far less capable of harnessing their minds to the task of healing their bodies, says the new research.

In clinical trials, a placebo is a “dummy” therapy, a sham version of the real thing. It helps give researchers a basis for comparison. If an experimental drug or treatment works far better than the placebo, its effect is presumed to be “real.” The “placebo effect” was long dismissed as an improvement that is “all in your head”: imagined, ephemeral, the response of the gullibly hopeful.

The problem is that the placebo effect is often very real, a powerful testament to the mind’s influence over physical pain, infection and disease. The belief that a treatment will work can help mobilize the immune system, blunt pain and promote healing.

For doctors, knowing who is most, and least, responsive to the placebo effect can be a useful clue to which patients are primed to heal and which may need more aggressive therapy. And for researchers trying to disentangle a treatment’s direct effects from those supplied by the study participant, it would be helpful to know which subjects would probably respond irrespective of whether they get the real thing or the sham.

Now, both have their answer, published this month in the journal Neuropsychopharmacology. About 50 volunteers at the University of Michigan completed assessments that nail down personality traits known to stay stable across most people’s life spans. In addition to gauges of altruism and empathy, they completed measures of neuroticism, extroversion, openness to experience, agreeableness and conscientiousness.

The volunteers then had infusions of two forms of saline solution into their jaw muscles: one that was expected to cause pain and another that should not. They sometimes got a real pain reliever, and at others got a placebo, never knowing what combination of conditions they were getting. Not only did participants rate their pain and their pain relief regularly; their levels of the stress hormone cortisol — a good gauge of discomfort — were tested and the activity levels of their body’s own painkilling response in the brain were measured.

Those who experienced pain relief from the fake analgesic didn’t just report it; their brain showed that their body’s pain suppression mechanisms — the natural release of opioid-like chemicals in the brain — snapped into high gear. And when researchers looked to see which subjects responded most strongly to the placebos, they saw people who rated highly on measures of altruism and the capacity to withstand and overcome stressors. They also tended to be highly straightforward: more direct and frank in their approach to others, less guarded and not manipulative.

“People with those factors had the greatest ability to take environmental information — the placebo — and convert it to a change in biology,” said University of Michigan psychiatrist Dr. Jon-Kar Zubieta, the paper’s senior author and an expert on the placebo effect.