*Scientific American* has placed the following article on their web site:

Expect the Best? Placebos Are for You! New study links expectations of rewards to placebo effect

Individual expectations of rewards may explain why some people feel
better after receiving fake drug treatments–a phenomenon known as “the
placebo effect.”

A new study using different brain imaging techniques linked the
intensity of an individual’s placebo effect to the amount of dopamine (a
neurotransmitter involved in the pleasure and reward pathway) released
in a midbrain region called the nucleus accumbens. Researchers at the
University of Michigan at Ann Arbor specifically demonstrated that those
who were more responsive to phony pills were also more likely to expect
to win big in a gambling game.

“If you have the capacity to respond to reward, then you have the
placebo effect,” says neuroscientist and radiologist Jon-Kar Zubieta,
senior author of the new study published this week in Neuron.

Zubieta and colleagues initially worked with 14 healthy volunteers who
were told they would receive painful injections of a saline (benign
saltwater) solution in their jawbones. That shot would be followed by a
second one, which subjects were led to believe would either be a
painkiller or a placebo. In actuality, everyone received a placebo.
Participants continually self-reported (using a numerical scale) the
degree of pain, and researchers monitored their brains with positron
emission tomography (PET) scans.

The scans showed that half of the participants who believed they were
receiving painkillers reported feeling significantly less pain than did
other volunteers. Their dopamine levels were noticeably higher (than
that of the others) from the moment they were told they were receiving
authentic painkillers.

On a different day (so the original participants would think they were
involved in two distinct studies), researchers had the 14 subjects,
along with 16 new volunteers, play a game of chance; they scanned
participants’ brains via functional magnetic resonance imaging (fMRI)
while they played. Participants were told they could win or lose a
certain amount of money each round; they would then push a button to
determine the real take. Several of the participants showed a flurry of
activity involving dopamine release in the nucleus accumbens while
awaiting the outcome, indicating that they were expecting a reward.

The people whose nucleus accumbens lit up during the game also reported
greater relief from the sham painkillers. “What surprised me the most
was the strong link between this element of reward processing and the
fact that you can predict the placebo response,” Zubieta says. “The
placebo effect is a resiliency mechanism in the brain. … You don’t
[really] need the medication, you simply need to be convinced that
something is going to work.”

Tor Wager, a psychologist at Columbia University, says this work could
be helpful in developing new therapies that manage the expectations of
patients. “This study opens up a new avenue of studies for brain-based
interventions,” he says, “such as targeting the dopamine system” to
increase the placebo effect.