Background: The offset of a painful and unpleasant sensation can elicit pleasure. This phenomenon, namely pleasant pain relief PPR , is attracting growing interest in research. While the cold pressor test CPT has been frequently used to study the inhibition of pain by the administration of another painful stimulation inhibitory conditioned pain modulation; ICPM , a preliminary study from our research team has shown that CPT can also elicit a robust and long-lasting PPR. However, its effects on pain relief and inhibition vary greatly between subjects.
Although substantial research has been carried out on inter-individual variability in the case of ICPM, the same cannot be said of PPR. Therefore, the current study sought to identify clusters of healthy volunteers with similar dynamic pain responses during the CPT, using a data-driven approach, and to investigate the inter-subject variability for PPR and ICPM.
Methods: One hundred and twenty-two healthy volunteers were recruited. Statistical analyses were performed using group-based trajectory modelling. Results: Four trajectories groups were identified for CPT pain intensity and unpleasantness ratings with varying levels of tonic pain and pain sensitization e.
On the other hand, no differences were found between groups regarding ICPM efficacy percentage pain inhibition. Using a data-driven approach, it was shown that PPR at CPT offset differs between clusters of participants identified based on dynamic pain intensity and unpleasantness responses from CPT. Thus, it was brought to light that both the levels of tonic pain and pain sensitization underlie individual differences in PPR. In the future, studies on the inter-subject variability of PPR in large samples of chronic pain patients are warranted.
Pain is an unpleasant sensation that we tend to avoid. The natural motivation to avoid pain and seek reward is an essential survival mechanism as it prevents harm and injury. However, pain can also become chronic in which case it loses its original purpose of protective properties and has, too often, devastating consequences on those who suffer from it, on their relatives and on society 2 — 4. Chronic pain states are often bidirectionally related to comorbid conditions, like depression and anxiety 7.
