Expectations regarding the intensity of pain can become self-fulfilling prophecies

Expect the blow to be hurt and this will probably be the case even if the needle sting is not really painful. Get ready for a second shot and you will probably back off again, although for the second time you should know better.

This is what must be remembered from a new brain imaging study published in the journal Nature human behavior which revealed that expectations regarding the intensity of pain can become self-fulfilling prophecies. Surprisingly, these false expectations can persist even when reality repeatedly shows the opposite, according to the study.

"We discovered that there was a positive feedback loop between expectations and pain," said lead author Tor Wager, a professor of psychology and neuroscience at the University of Colorado at Boulder. . "The longer you wait for pain, the more pain your brain responds to – the more pain your brain responds to, the more you expect."

For decades, researchers have been intrigued by the idea of ​​a self-fulfilling prophecy. Studies showing that expectations could influence everything from the way you test to how you react to a drug. This new study is the first to directly model the dynamics of the feedback loop between expectations and pain and the underlying neural mechanisms.

Marieke Jepma, then a postdoctoral researcher in Wager 's lab, started the research after finding that even when the test subjects were exposed over and over again to the idea that something would not hurt, some of the s & #' s They waited there.

"We wanted to better understand why the expectations of pain are so resistant to change," said Jepma, lead author and now researcher at the University of Amsterdam.

The researchers recruited 34 subjects and taught them to associate one symbol with a low heat and another with an intense and painful heat.

Then the subjects were placed in a functional magnetic resonance imaging (fMRI) device, which measures the blood flow in the brain as a proxy for neural activity. For 60 minutes subjects were shown low or high pain indices (symbols, low or high words, or the letters L and W), then asked to assess the expected level of pain.

Then, different degrees of painful but non-damaging heat were applied to the forearm or leg, the hottest reaching "what it feels like to hold a cup of hot coffee," says Wager.

Then they were asked to rate their pain.

Unbeknownst to the subjects, the heat intensity was in fact not related to the previous signal.

The study found that when subjects expected more heat, brain regions involved in fear and threat were more activated while waiting. Regions involved in pain generation were more active when they received the stimulus. Participants reported more pain with intense pain signals, regardless of how much heat was actually released.

"This suggests that expectations have had a profound effect, influencing how the brain treats pain," Jepma said.

Surprisingly, their expectations also strongly influenced their ability to learn from their experiences. Many subjects have demonstrated a high "confirmation bias" – the tendency to learn from things that reinforce our beliefs and neglect those that are not. For example, if they were expecting intense pain and getting it, they could expect even greater pain next time. But if they expected intense pain and did not understand it, nothing changed.

"You would assume that if you were expecting a lot of pain and you got very little, you'd know better next time, but oddly, they did not learn," Wager said.

This phenomenon could have tangible effects on the recovery of painful conditions, suggests Jepma.

"Our results suggest that negative expectations about pain or treatment outcomes may, in some situations, interfere with optimal recovery, both by improving perceived pain and preventing people from perceiving that they are not getting better. they are improving, "she said. "On the other hand, positive expectations could have the opposite effects."

The research could also explain why, for some, chronic pain may persist long after healing of damaged tissue.

Whether in the context of pain or mental health, the authors suggest that it may be good for us to become aware of our eagerness to confirm our expectations.

"Just realizing that things may not be as bad as you think can help you review your expectations and, in so doing, change your experience," Jepma said.