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Friday, September 20, 2019
Home Specialties Pain Management Expectations of Pain Can Influence Actual Sensation

Expectations of Pain Can Influence Actual Sensation

Can pain be a self-fulfilling prophecy? Maybe. 
Getting vaccinated, stubbing a toe, or even breaking a finger can hurt. Medical procedures in general can be painful and cause patients varying degrees of distress. But the expectation of pain can potentiate the actual feeling and sometimes pain may be experienced because its expected. These false expectations can persist even when reality shows otherwise, according to researchers of a new study. 

The idea that expectations can strongly influence how events are experienced is not a new one, as expectations can influence everything from how one performs on a test to how one responds to a medication. In fact, the idea of expectations underlies the whole “placebo effect” in medicine. In many clinical trials, some patients receive the active drug while other get an inactive placebo, and yet results sometimes show little difference between the groups. Even when it comes to side effects, some patients will experience the “drug related” toxicities even though they are taking a benign sugar pill. This “bidirectional interaction” between expectations and the actual experience can often result in a self-reinforcing phenomenon or the so-called “self-fulfilling prophecies.” This phenomenon can also be seen beyond medicine, such as in performance and behavior, and even in the larger societal realm of economic growth and recession.

A number of studies have looked at how experiences strongly affect perception and response to stimuli, especially pain. One study found that this may even be true with infants. When two infant immunizations are given during an office visit, the least painful should be given first, as it seemed to minimize the pain overall. The study authors hypothesized that giving the more painful injection first may focus the infant’s attention on the procedure and activate pain processing centers in the brain and amplify the pain signal during subsequent injections administered immediately thereafter.

In the current study, the investigators wanted to gain a better understanding of why pain expectations seem so resistant to change. They enrolled 34 individuals with the goal of evaluating their expected pain, reported pain and brain activity. The study participants were taught to associate one symbol with low heat and another with high, painful heat, and then underwent functional magnetic resonance imaging (fMRI), which measured blood flow in the brain as a proxy for neural activity. During a period of 60 minutes, the participants were shown low or high pain cues (the symbols, the words Low or High, or the letters L and W), then asked to rate how much pain they expected to feel. They were then exposed to varying levels of painful but non-damaging heat, with the hottest reaching “about what it feels like to hold a hot cup of coffee,” according to the investigators.

The individuals then rated their pain, not knowing that the actual heat intensity was unrelated to the cues that they had previously received. But they still reported feeling more pain with high-pain cues, regardless of how much heat they had actually received. The investigators noted that the “positive feedback loops between expectations and experiences can create self-fulfilling prophecies,” and that these beliefs, behaviors, and decisions continue to persist, as they are driven by initial expectations and remain resistant to corrective experience. The MRI scan showed that when they expected more heat, brain regions involved in threat and fear became more activated as they waited, while regions involved in the generation of pain were more active when the stimulus was actually received. 

“This suggests that expectations had a rather deep effect, influencing how the brain processes pain,” say the investigators, and note that this research may have clinical implications for patients who continue to experience chronic pain long after they have healed. 

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