Investigating the Influence of Cues on Pain Perception: A Bayesian Model Selection Approach

The intensity of noxious stimuli usually shapes the perception of discomfort or pain. Here, we compare three mechanistic accounts of how cued expectation about stimulus intensity may modulate behavioral reports of discomfort: response gain, input gain or baseline shift. In two behavioral sessions, thirty-nine healthy participants rated a series of 160 uncomfortable electrical stimuli (UES) applied to the skin of the forearm, preceded by a visual cue indicating the intensity of the upcoming stimulus as 'weak' or 'strong'. Cue contingency of 65% or 70% varied between the two sessions to investigate the effect of informativeness on putative modulatory cueing effects. We found that verbal cueing of the expectation of an upcoming UES biased subjects' ratings towards the expected outcome. A Bayes factor analysis revealed that of the three putative modulatory processes, the baseline shift model received the strongest support from our empirical data. Manipulating the level of contingency of the cue did not further alter the results. We conclude that, within the parameters of our experiment, expectations influence the perception of the UES independently of stimulus intensity. Extending these findings to a clinical context may improve our understanding of hypersensitivity in chronic pain patients.