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Study design. Before randomization, participants were instructed and a cover story was provided. Participants were told that in this study, changes in electrodermal activity (EDA) would be assessed as a measure of the autonomic nervous system during experimental heat stimuli and used to predict the perception of pain (cover story). Participants were assigned to either i) the hypoalgesic group with suggestion towards profound hypoalgesia following the temperature reduction, ii) the hyperalgesic group with verbal suggestion towards hyperalgesia following the temperature reduction (see the example above), or iii) the control group with no intervention. Regardless of the group assignment participants were exposed to two offset and two constant trials provided in a counterbalanced manner.
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A frequently used paradigm to quantify endogenous pain modulation is offset analgesia, which is defined as a disproportionate large reduction in pain following a small decrease in a heat stimulus. The aim of this study was to determine whether suggestion influences the magnitude of offset analgesia in healthy participants. A total of 97 participant...
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Context 1
... participants provided oral and written informed consent. An overview of the study design is provided in Fig 1. ...
Context 2
... OT, the temperature first increased to 46˚C (T1) for 10 seconds, then increased to 47˚C (T2) for 10 seconds, and finally decreased again to 46˚C (T3) lasting 20 seconds. The temperature pattern of the two trials can be seen in Fig 1. These figures were shown to the participants before the application of the heat stimuli. ...
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... Yet the circuits that underpin placebo analgesia and the response to a CPM paradigm are different. This paradox could indicate that the body has many metaphorical strings to anisms underlying offset analgesia are unknown, 23 but it likely activates pathways that are distinct from those underlying the CPM response. 24 When researchers test for offset analgesia, they apply 3 heat stimuli to the person's skin. ...
The information in this editorial does not provide the necessary, nor sufficiently detailed, level of information required to know how or when to prescribe analgesic drugs. Instead, we aim to provide a summary of relevant information for all health care providers who work with patients who are suffering from chronic pain. If you have questions or ideas for past or new editorials in the #PainScienceIn-Practice series, please get in touch via JOSPT's social media channels (using #PainScienceInPractice) or via email. MEASURING DESCENDING PAIN MODULATION IN HUMANS The DPMS is an interconnected and often mutually interacting system of circuits (neuronal pathways) (Hoegh MS, Bannister K. Pain science in practice (part 6): how does descending modulation of pain work? J Orthop Sports Phys Ther. 2024;54:1-4.) Measuring the activity of individual circuits in humans is not currently possible. However, it is possible to test the net response of inhibitory and facilitatory modulatory actions in the DPMS. A range of paradigms (ie, standardized ways used within research) have been developed for this purpose. In the next section, we describe the most common paradigms.
Pain perception is influenced not only by sensory input from afferent neurons but also by cognitive factors such as prior expectations. It has been suggested that overly precise priors may be a key contributing factor to chronic pain states such as neuropathic pain. However, it remains an open question how overly precise priors in favor of pain might arise. Here, we first verify that a Bayesian approach can describe how statistical integration of prior expectations and sensory input results in pain phenomena such as placebo hypoalgesia, nocebo hyperalgesia, chronic pain, and spontaneous neuropathic pain. Our results indicate that the value of the prior, which is determined by generative model parameters, may be a key contributor to these phenomena. Next, we apply a hierarchical Bayesian approach to update the parameters of the generative model based on the difference between the predicted and the perceived pain, to reflect that people integrate prior experiences in their future expectations. In contrast with simpler approaches, this hierarchical model structure is able to show for placebo hypoalgesia and nocebo hyperalgesia how these phenomena can arise from prior experiences in the form of a classical conditioning procedure. We also demonstrate the phenomenon of offset analgesia, in which a disproportionally large pain decrease is obtained following a minor reduction in noxious stimulus intensity. Finally, we turn to simulations of neuropathic pain, where our hierarchical model corroborates that persistent non-neuropathic pain is a risk factor for developing neuropathic pain following denervation, and additionally offers an interesting prediction that complete absence of informative painful experiences could be a similar risk factor. Taken together, these results provide insight to how prior experiences may contribute to pain perception, in both experimental and neuropathic pain, which in turn might be informative for improving strategies of pain prevention and relief.
Author summary
To efficiently navigate the world and avoid harmful situations, it is beneficial to learn from prior pain experiences. This learning process typically results in certain contexts being associated with an expected level of pain, which subsequently influences pain perception. While this process of pain anticipation has evolved as a mechanism for avoiding harm, recent research indicates overly precise expectations of pain may in fact contribute to certain chronic pain conditions, in which pain persists even after tissue damage has healed, or even arises without any initiating injury. However, it remains an open question how prior experiences contribute to such overly precise expectations of pain. Here, we mathematically model the pain-learning-process. Our model successfully describes several counterintuitive but well-documented pain phenomena. We also make predictions of how prior experiences may contribute the perception of pain and how the same learning process could be leveraged to improve strategies of pain prevention and relief.
