Material below summarizes the article Doubling Your Pay-Off: Winning Pain Relief Engages Endogenous Pain Inhibition, published on August 25, 2015, in eNeuro and authored by Susanne Becker, Wiebke Gandhi, Saskia Kwan, Alysha-Karima Ahmed, and Petra Schweinhardt.
The pleasure of pain relief is known to everyone — satisfying, soothing, and much sought-after when one is in pain. For individuals suffering from chronic pain, pain relief is a major, often all-dominant, goal.
It is known that motivation to obtain reward augments the liking of the reward when obtained. Because pain relief can be conceptualized as a form of reward, we reasoned that a reduction of nociceptive input that is obtained in a motivated state should be associated with greater pain reduction than expected by the decreased nociceptive input.
In our study, healthy participants played a computerized Wheel of Fortune game because the chance of winning induces a motivated state in humans. When participants won in the game, they obtained a decrease in nociceptive input, whereas when they lost, they received an increase of nociceptive input. The magnitude of pain that participants felt when they won a decrease in nociceptive input was compared to a control condition in which participants received the same decrease in nociceptive input without winning it.
Before the start of the experiment, participants’ skin on the forearm was sensitized using the TRPV1-receptor agonist capsaicin, the pain-inducing component of chili pepper. Heat was applied superficially to the sensitized area using a computer-controlled thermode.
At the beginning of a trial, the temperature of the thermode increased to a pre-determined and individually adjusted temperature that provoked a moderate level of pain. Then participants played the Wheel of Fortune game. If the wheel landed on the color they had chosen, the outcome "you won" was displayed and the temperature of the thermode was reduced. In contrast, if the wheel did not land on the color the participant had selected, the outcome ‘you lost’ was displayed and temperature of the thermode increased.
In the control condition, participants could not chose the color the wheel would land on and therefore, could not win or lose. However, they received the same temperature reductions and increases as in the experimental condition.
Pain was assessed just after the outcome phase in two ways: subjective ratings and an adjustment task where participants adjusted the heat intensity to the intensity they remembered from the beginning of the trial. This method provides a more objective pain measure less influenced by reporting bias than pain ratings. The difference in subjectively rated pain intensity as well as objectively measured pain sensitivity between the experimental and the control conditions served as measure whether winning a reduction in temperature led to lower pain levels compared to passively obtaining the same temperature reduction.
Results confirmed our hypothesis and showed that pain was lower when participants won the temperature reduction. This effect was observed in the subjective ratings as well as in the objective assessment, which showed that participants sensitized less to the heat stimulation when they won the temperature reduction compared to the control condition without winning.
These results indicate that pain relief when obtained in a motivated state engages endogenous pain inhibition.
These results are important in a clinical context because they might help improving behavioral therapy of chronic pain. Positive and negative reinforcement is already used in pain therapy to promote healthy behaviors and reduce maladaptive behaviors. Using pain relief as negative reinforcement might be of particular benefit because pain relief is typically the major goal of chronic pain patients and therefore associated with strong motivation. Consequently, a positive, self-amplifying feedback loop of reduced pain and improved functionality might be induced, possibly leading to long-lasting improved functionality and reduced pain in chronic pain patients.
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Doubling Your Payoff: Winning Pain Relief Engages Endogenous Pain Inhibition. Susanne Becker, Wiebke Gandhi, Saskia Kwan, Alysha-Karima Ahmed, Petra Schweinhardt. eNeuro Jun 2015, 2 (4) DOI: 10.1523/ENEURO.0029-15.2015
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