This is Scientific American ― 60-Second Science. I'm Karen Hopkin.Getting a vaccine can be a painful experience, especially when you're a kid.But getting told the shot might "hurt a bit" could actually make it worse."We know that expectation affects pain experience in adults.But we don't really know whether this is also true for children."Kalina Michalska, a developmental neuroscientist at the University of California, Riverside. She led a study to find out.The study included 25 adults and 48 children. And 27 of the kids had a pre-existing anxiety disorder.Because medical procedures make pretty much all kids anxious...and those who are anxious to start with tend to find the experience even more painful.The researchers used a handheld wand to apply heat to the forearm of each participant.And they asked subjects to rate the temperature in terms of discomfort.The hottest setting was about the temperature of very warm tap water―uncomfortable, perhaps, but not damaging."But during the experiment, we were most interested in only one temperature: the one that each subject rated as medium."That's where the "anticipation" part of the experiment comes in.Subjects were played one of two tones."One tone meant that low heat was coming; the other meant that high heat was upcoming."But here's the sneaky part.No matter what tone was played, participants got the same heat applied―the one rated as "medium.""So even though the subject heard a cue indicating high pain or low pain, the pain was only medium."Or at least that's how it should have felt.But what happened was that subjects reported feeling what they thought they would.
