Why placebo works? Scientists say that our expectations form the perception of pain

Placebo is a strange thing. When people experiencing pain are given placebo, sometimes they immediately feel better just because they think they got some effective pain killers. Even scientists are surprised to see it work again and again. Now researchers from the University of Colorado Boulder and the University of Amsterdam say that our expectations influence how we perceive pain and what we learn from it.

Placebo pills work because people expect them to work – expectations for the perception of pain. Image credit: Michelle Tribe via Wikimedia(CC BY 3.0)

Scientists performed a couple of very interesting experiments. They invited some participants and sat them down with a heating device, which could cause pain. They had to look at some visual cues that were associated with the amount of pain that was administered. Of course, the brain activity of these participants was being monitored in order to see how pain is perceived. Then in the second stage of the experiments visual cues no longer represented the level of pain administered. This allowed scientists seeing a couple of things – whether visual cues influenced the perception of pain and if participants learned that these cues did not mean anything in the second stage.

Scientists found that visual cues cause certain expectations, because they are related to pain levels. And these expectations are met, regardless of how hot the thermode got. The more pain people expected, the more pain they felt. When pain was stronger than expected, participants learned to expect higher levels of pain. When it was not as strong, they expected less pain next time. But people learn more from experiences that are consistent with their expectations. This is a well-known phenomenon called the confirmation bias – people’s expectations are rigid even when confronted with evidence that suggest the opposite.

This phenomenon can have positive and negative implications, depending on the situation. If you expect to be in pain and find yourself pain-free, you may not think you are recovering and consider it a placebo effect or even a coincidence. Marieke Jepma, one of the authors of the study, named an opposite example as well – “if you expect pain relief but do not experience less pain, you may attribute this to ‘having a bad day’ rather than realizing that the treatment you’re taking is not working. These processes possibly play an important role in the development of chronic pain”.

Living in pain is a terrible experience and people are trying to avoid it by all means possible. However, not all pain is possible to treat effectively and sometimes patients are not helping by expecting even more pain. That is why placebo is so effective – people expect these miraculous drugs to work. It is almost like it is a positive lie.


Source: University of Amsterdam


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