Perception of repeated pain relief with controllable and uncontrollable pain.

BACKGROUND: The ultimate goal of pain research is to provide effective routes for pain relief. Nevertheless, the perception pain relief as a change in pain intensity and un-/pleasantness has only been rarely investigated. It has been demonstrated that pain relief has rewarding and reinforcing properties, but it remains unknown whether the perception of pain relief changes when pain reductions occur repeatedly. Further, it remains an open question whether the perception of pain relief depends on the controllability of the preceding pain. METHODS: In this study, healthy volunteers (N = 38) received five cycles of painful heat stimulation and reduction of this stimulation to a non-painful warm stimulation once in a condition with control of the stimulation and once without control. Participants rated perceived intensity and un-/pleasantness on visual analogue scales during the heat stimulation and immediately after its reduction. RESULTS: Results showed that perceived pain relief, estimated by the difference in ratings during ongoing heat stimulation and after its reduction, increased with repetitions. However, this increase levelled off after two to four repetitions. Further, perceived pain relief was larger in the condition without control compared to the condition with control. CONCLUSION: The perception of pain relief can be modulated similar to the perception of pain by stimulus characteristics and psychological factors. Mechanistic knowledge about such modulating factors is important, because they can determine, e.g., the amount of requested pain killers in clinical settings and the efficacy of pain relief as a reinforcing stimulus. SIGNIFICANCE: When in pain, pain relief can become an all-dominate goal. The perception of such pain relief can vary depending on external and internal characteristics and thus modulate, e.g., requests for pain killers in clinical settings. Here, we show that perceived intensity and pleasantness of pain relief changes with repetitions and whether the preceding pain is perceived as uncontrollable. Such mechanistic knowledge needs to be considered to maximize the effects of pain relief as a rewarding and reinforcing stimulus.

What does "moderate pain" mean? Subgroups holding different conceptions of rating scales evaluate experimental pain differently.

BACKGROUND: Pain ratings are almost ubiquitous in pain assessment, but their variability is high. Low correlations of continuous/numerical rating scales with categorical scales suggest that individuals associate different sensations with the same number on a scale, jeopardizing the interpretation of statistical results. We analysed individual conceptions of rating scales and whether these conceptions can be utilized in the analysis of ratings of experimental stimuli in pain-free healthy individuals and people with reoccurring/persistent pain. METHODS: Using a free positioning task, healthy participants (N = 57) and people with reoccurring/persistent pain (N = 57) ad libitum positioned pain descriptors on lines representing intensity and un-/pleasantness scales. Furthermore, participants rated experimental thermal stimuli on visual analogue scales with the same end anchors. A latent class regression approach was used to detect subgroups with different response patterns in the free positioning task, indicating different conceptions of pain labels, and tested whether these subgroups differed in their ratings of experimental stimuli. RESULTS: Subgroups representing different conceptions of pain labels could be described for the intensity and the un-/pleasantness scale with in part opposing response patterns in the free positioning task. Response patterns did not differ between people with and without pain, but in people with pain subgroups showed differential ratings of high intensity experimental stimuli. CONCLUSIONS: Individuals' conceptions of pain labels differ. These conceptions can be quantified and utilized to improve the analysis of ratings of experimental stimuli. Identifying subgroups with different conceptions of pain descriptions could be used to improve predictions of responses to pain in clinical contexts. SIGNIFICANCE: The present results provide a novel approach to incorporate individual conceptualizations of pain descriptors, which can induce large distortions in the analysis of pain ratings, in pain assessment. The approach can be used to achieve better pain estimates, representing individual conceptions of pain and achieving a better comparability between individuals but also between pain-free persons and patients with chronic pain. Particularly, in clinical settings this could improve quantification of perceived pain and the patient-clinician communication.