You’ll hardly feel a thing. If doctors play down the pain of a procedure, patients might avoid the nocebo effect – the placebo effect’s evil twin.

Arne May‘s team at the University of Hamburg, Germany, applied heat to the arms of 38 volunteers over six days. Half of them were told the heat would get more intense, and they reported constant pain levels. The rest felt less pain as they got used to the sensation. The first group also had increased activity in a brain area involved in pain perception.

“I didn’t expect that giving negative information for 5 minutes would have an effect a week later,” May says.

Journal reference: The Journal of Neuroscience, DOI: 10.1523/jneurosci.2197-10.2010