Harvie D.1
1Griffith University, Recover Injury Research Centre, Menzies Health Institute QLD, Gold Coast, Australia
Background: The multidimensional nature of pain has been highlighted by research showing that factors from sensory, cognitive, and emotional domains modulate pain. Remarkably, non-nociceptive information can not only modulate, but in certain cases, evoke pain. Since pain might best be described as a response to credible signals of bodily danger, non-nociceptive factors might be able to contribute to pain when they meet this criterion. One-way non-nociceptive cues become danger signals, is by prior association with painful-events. For example, if rotating the neck repeatedly provokes pain in an acute scenario, then that movement could become a pain-sensitising signal of threat by association.
Purpose: To test whether pain-associated cues could contribute to pain.
Methods: In three separate studies, the ability of pain-associated tactile, contextual and kinesthetic cues to modulate pain was tested. In two laboratory classical conditioning studies, healthy subjects underwent a learning phase where specific tactile stimuli (n = 54) and specific virtual reality environments (n = 25) were associated with painful stimulation, while other stimuli were not. In a test phase the effect of the pain-associated stimuli on noxious-evoked pain and mechanical pain thresholds was tested. In a third study, we tested whether pain-associated kinesthetic cues could modulate pain with movement independent of actual movement, in people with persistent neck pain (n = 24). This was tested by asking participants to rotate their neck to their first onset of pain, in conditions where the virtual reality displayed over- or under-stated movementcreating the perception of more or less movement that was actually occurring. The change in neck rotation range of movement to first pain was compared between conditions (i.e. Movement-evoked pain threshold).
Results: In the laboratory studies, pain-associated tactile and environmental cues mediated an increased in perceived intensity of concurrently presented nociceptive stimuli (p 0.05), and resulted in a reduction in mechanical pain thresholds (p 0.05). In the clinical study, neck pain with movement depended on the perceived, not only actual movement (p 0.05). Secondary outcomes suggest the ability of pain-associated cues to modulate pain is subconscious, and independent of explicit expectation.
Conclusion(s): Pain-associated cues enhance pain, suggesting that associative learning contributes to a unique form of central sensitivity.
Implications: Pain-associated cues are by synonymous with aggravating factors, and are therefore routinely and expertly identified by physiotherapists. While these pain-associated cues/aggravating factors are typically classified as mechanical signs, they are also signals of threat that might contribute to pain via central mechanisms. The finding that pain associated cues augment pain, has implications for physiotherapy in that they suggest that techniques that aim to extinguish associations between pain and movement, such as expertly guided graded activity or graded motor imagery, might improve outcomes.
Funding acknowledgements: Nil
Topic: Pain & pain management
Ethics approval: Projects were approved by Griffith University (2016/242) and University of South Australia ethics boards (31537; 31100).
All authors, affiliations and abstracts have been published as submitted.
