Sometimes you get what you expect. That might be a nice thought around Christmas, but it can be a pain in the neck when we expect something nasty like, well, pain.

Researchers at the University of Colorado found in a recent study that our expectations about how painful something is going to be turn into self-fulfilling prophecies. Expect a painful shot at the doctor’s office, and it will, in fact, be painful, even if the actual needle poke is a piece of cake.

Researchers described this effect as a positive feedback loop, and an irksome one at that.

They showed 34 study volunteers two symbols and taught them to associate the first with low heat, the second with painful heat.

Their brains were then scanned for blood flow while researchers applied heat to a forearm or leg as the participants were shown one or the other symbol. The worst heat applied was about the intensity of a hot cup of coffee.

Researchers, however, performed some sleight of hand. The heat intensity applied had no relation to the symbols. So the painful-heat symbol could be applied with the low-pain symbol and vice versa.

The volunteers, however, reported more pain when they saw the symbol associated with uncomfortable heat, even when a low-heat stimulus was applied.

Brain flow suggested that threat and fear portions of the brain were more active when the participants were waiting for the stimulus and expecting more pain.

The findings could have important health implications and might help explain why chronic pain lingers even after injuries have long healed.

And if nothing else, the study might make your next visit to the doctor for a shot a little more tolerable.