Placebos, Dopamine and Your Nucleus Accumbens


New drugs are generally tested in randomized control trials in which half of a group of patients get the new therapy and half get the equivalent of a sugar pill. It is well-known that a lot of people taking sugar pills feel better. This is known as the placebo effect—the phenomenon in which a patient's symptoms are alleviated by an otherwise ineffective treatment, apparently because the individual expects or believes that it will work.

Brain scanning researchers at the University of Michigan believe that they have pinpointed why the placebo effect works in some patients and why others are immune to it. The press release reporting the new study notes:

Using two different types of brain scans, U-M researchers have found that the extent to which a person responds to a placebo treatment is closely linked to how active a certain area of their brain becomes when they're anticipating something beneficial.

Specifically, the research finds strong links between an individual's response to a placebo "painkiller", and the activity of the neurotransmitter known as dopamine in the area of the brain known as the nucleus accumbens. That's a small region at the center of the brain that's involved in our ability to experience pleasure and reward, and even to become addicted to the "high" caused by illicit drugs.

The researchers injected volunteers with a painful saline solution and then told them that some would receive a painkiller injection and others would receive a placebo. In fact, all of the "painkiller" injections were placebos.

The PET scans and pain ratings revealed that as a group, the volunteers experienced significant pain relief from the placebo. But when researchers looked at each individual's results, they found that only half of the volunteers reported less pain when they received the "painkiller" placebo.

These placebo responders, as they were dubbed, had significantly more dopamine activity in their left nucleus accumbens than the other volunteers, beginning when they were told the painkiller medicine was about to begin flowing into their jaws. It also turned out that these individuals had also all anticipated the "painkiller" would give good pain relief before they even received it.

Meanwhile, of the seven individuals who didn't experience the placebo effect, four actually reported feeling more pain when the "painkiller" was delivered – a phenomenon that has been dubbed the "nocebo" effect and has been observed in other situations.

My speculative question is would weeding out placebo responders through pre-clinical trial brain scanning improve the process of determining the efficacy of new drugs?