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Thursday, July 19, 2007

The placebo effect, dopamine and reward

"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.
In this study they used brain imaging techniques. The 14 volunteers were told they would receive painful injections of saltwater in their jaw muscles. This shot would be followed by a painkiller. Half of the volunteers would receive the painkiller and the other half would be injected a fake painkiller, so they were told. However all volunteers were injected with the fake painkiller (placebo). During this procedure they were monitored with brain imaging techniques (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 another day these fourteen with 16 new volunteers were brain scanned with functional magnetic resonance imaging (fMRI) during a card gambling game. They 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. These participants were also the people reporting pain relief from the fake painkiller. So there is a strong link between the reward system (dopamine, nucleus accumbens) and the placebo effect. With this result you can predict the placebo response or even develop techniques targeting the dopamine system to increase the placebo effect.

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