SOUL/BODY: Tracking Placebos in the Brain

by Sheldon Lewis

Scientists have long been puzzled by the fact that a placebo — a “sugar pill” or sham treatment — relieves such symptoms as pain for some people, but either does nothing for others or makes them feel worse. Using brain scanning technology, researchers from the University of Michigan Health System may have an explanation: our response to a placebo is linked to the amount of activity in a part of the brain’s pleasure-and-reward center called the nucleus accumbens.

In the study, published in the journal Neuron, the Michigan team performed PET scans on the brains of 14 healthy volunteers while they were told to expect, and then when they were given, a painful saline injection in their jaw muscle. Then they were told they would be given a second injection — of either a painkiller or a placebo — but both injections were, in fact, placebos.

About half of the volunteers responded to the placebo, with their bran scans showing significantly more activity of the brain chemical dopamine in the nucleus accumbens than the other volunteers — beginning when they were told to expect the second injection. And these same placebo responders had expected that the “painkiller” would relieve their pain.

The researchers concluded that response to placebo is “proportional to the amount of benefit that the individual anticipates,” according to the study’s senior author, neuroscientist and psychiatrist Jon-Kar Zubieta, M.D., Ph.D.
Another type of brain scan, called fMRI, produced similar results, showing that neurons in the nucleus accumbens were very active when people expected to win or lose a reward in a gambling game. Strikingly, those with the most active nucleus accumbens while anticipating a reward were also those whose pain responded to the placebo.

“This is a phenomenon that has great importance for how new therapies are studied,” says Zubieta. And our response to placebo may signal how resilient our brains are, especially when we’re anticipating something good.