Placebo gives brain emotional break

The placebo effect, in which people experience health benefits from inactive medications, thrives on great expectations. According to a new study of placebo-induced reduction of anxiety, such expectations trigger a decline in the brain’s emotional responsiveness and marshal pain-numbing neural activity.

A team led by Predrag Petrovic of the Karolinska Institute in Stockholm tested 15 women over 2 days. On the first day, each volunteer used a scale of 1 to 100 to rate the unpleasantness of pictures presented to her. For example, a picture of severely injured people got high rankings and a landscape ranked low. Participants then received low intravenous doses of an antianxiety drug and rated the images a second time. Finally, the women rated the same images after receiving intravenous doses of a substance that blocked the antianxiety drug’s effects.

With the antianxiety treatment, they viewed the images with less unease the images that they had previously rated as highly unpleasant. With the blocker of the antianxiety drug, the women’s’ ratings duplicated their initial ones.

The next day, the experiment was repeated, with a placebo twist. Volunteers were told they would get the same two drugs, but they instead received intravenous saline. Unpleasantness ratings in each condition closely corresponded to ratings from the previous day, Petrovic and his coworkers report in the June 16 Neuron.

A functional magnetic resonance imaging scanner measured blood flow—a sign of neural activity—in each woman’s brain during the placebo experiments. When a placebo eased distress at seeing disturbing images, activity in brain areas linked to emotion died down. Moreover, regions previously implicated in pain relief from placebos perked up, the researchers note.

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.