There might be something to positive thinking after all - and it's not just in your head.
Researchers at the University of Michigan, Princeton and several other universities say that electronic signals fired off in the brains of 48 volunteers show that the brain reacts differently to pain when someone is given a placebo and believes in it.
"How much the placebo effect is felt correlates with how much you believe," said Tor D. Wager, lead author of the study, who was a Michigan researcher during the project and is now a psychology professor at Columbia University.
The report, described as the first major study of its kind, was published in today's Science.
Wager's group conducted two experiments, subjecting 24 people to electrical shocks and 24 others to a heated patch on their arms. Volunteers were paid $75 each and were subjected to pain levels ranging from slight to moderate. The shocks were administered in one-second intervals and the heat was applied in 20-second periods.
"I think of it as a general 'ow' kind of pain, like holding on to a really hot cup of coffee. ... You can stand it, but you really don't like it," Wager said.
Fewer brain signals
About 70 percent of the subjects said they felt less pain when a placebo skin cream was applied, according to the study. Follow-up MRIs on those subjects showed that the pain centers in their brains fired off fewer signals when placebos were given.
"With a placebo you're creating a belief or expectation, and we found that the expectation is being processed into what is experienced," Wager said.
Placebo research is aimed at broadening scientific understanding of the brain and of neurological disorders that affect it. Such studies might lead to development of therapies for depression, Parkinson's' and other long-term illnesses now treated with medications that can have side effects when taken in steady doses.
The placebo effect has long been recognized, but scientists continue to debate its significance.
Skeptics say the benefits attributed to placebos might flow from the body's ability to heal itself without treatment or medication. Three years ago, researchers at the University of Copenhagen in Denmark concluded that health benefits attributed to placebos were the result of diseases running their course.
But believers say there must be some reason that placebos in controlled experiments have the desired benefit about 30 percent of the time.
"There's always been two viewpoints: One, that placebos don't exist; and the other, they can trigger real biological-based events," said Dr. Donald D. Price, a neuroscientist at the University of Florida who uses brain images to analyze placebo effects.
Price said that Wager's study is the first to use MRIs to measure the effect of placebos on cerebral pain centers. Previous studies used fewer test subjects or PET scans, which failed to show how pain centers were responding to impending jolts of pain.
Price said studies show that placebo benefits increase if the recipients are confident they will help.
"If a researcher wears a white lab coat, if they talk in a soothing voice, if they instill an aura of confidence as a professional, the placebo can have dramatic effects," Price said.
Studies have shown that Parkinson's patients, in particular, respond to placebos. People with Parkinson's have tremors, jerky movements and a general loss of muscle control - the result of too little dopamine being released into their brains. In 2001, researchers from the University of British Columbia found that a placebo caused dopamine to be released in all six of the Parkinson's patients tested.
A study at the University of Texas Health Sciences Center in 2002 found that four of 17 men hospitalized for depression responded to a placebo after six weeks of treatment. The same number responded to fluoxetine, a popular treatment for depression. Nine of the men failed to improve.
But outside of clinical studies, doctors say, using placebos for treatment is improper because patients deserve the truth about their medications.
Experts also say it is difficult to measure pain in scientific studies because it is so subjective.
"It's hard to compare any two people because people can be so very different," said Dr. Carla S. Alexander, head of palliative care at the University of Maryland Medical Center, where she treats patients with cancer, AIDS and other illnesses. "Some people are incapacitated by pain, and others take it in stride."
The fact that people have different individual pain thresholds makes it difficult to evaluate what they are experiencing, Alexander said: "I'd be interested in knowing the backgrounds of the test subjects."
Wager said the test subjects were a cross-section of residents living around the campuses of Princeton and Ann Arbor, Mich. Volunteers in Princeton were given electrical shocks on their wrists; volunteers in Ann Arbor had heat applied to patches on forearms.
The researchers told the subjects the study was measuring brain responses to two skin creams. One they were told would reduce pain, while the other should not. Researchers applied the same lotion in every case.
The MRIs showed a difference in the electronic signals fired off in several key cerebral pain centers, including the thalamus, insula and anterior cingulate cortex.
Wager said the study shows that expectations are a key in determining how painful something feels and why the pain from a rigorous workout might feel less traumatic than the pain from a kick or a punch.
"The pain you feel in a gym might not hurt as much because you know it's benefiting you or you've felt it before and you're familiar with it," he said.