Untangling the perception of pain: certainty in sensations as a modulator of the effects of top-down mechanisms on pain perception

The perception of pain is the result of an integration of multiple complex mechanisms. The current leading model that explains the modulation of pain, combining the arising sensory information and top-down factors is the Bayesian Brain Hypothesis (BBH). The BBH suggest that perception is a prediction process weighted by precision of the prior (i.e., expectations, prior experience, contextual cues) and the likelihood (actual sensory information). While the influence of expectation and its certainty as a modulator of pain experience has been extensively studied, less attention has been devoted to the certainty of the ascending nociceptive signals. One of the reasons may be the lack of established measures to estimate it. In the last years, a tool which allows to quantify within-subject-variability in response to experimental pain, the Focused Analgesia Selection Test (FAST) was developed, proving potential information concerning the estimation of the certainty of sensory signals. The aim of this dissertation is to test a recently published hypothesis by our group, that the FAST might be a valid measure to estimate the certainty of sensory signals. If true, better certainty (lower variability in the FAST) may be associated with reduced effects of expectations on perception and, therefore, perception becomes closer to the real sensory signals arising from the peripheral stimulation. On the other hand, lower precision in sensory information (higher variability in the FAST) may imply that the subjective experience will be more influenced by expectations and therefore will deviate from the expected pain elicited by a given stimulus intensity. To test this hypothesis participants will be invited to two study visits. In the first visit, subjects will perform the FAST procedure and the experimental placebo paradigm, after which participants will be selected to a second visit based on their performance on VI FAST. Only those with large and low variability (top and bottom 25%) will be enrolled into the second study visit, in which the cued-pain observation paradigm will be performed, alongside with EEG recording to capture contact-heat evoked potentials and brain oscillations. Autonomic responses (electrocardiogram and electrodermal activity) and relevant psychological characteristics will be assessed to provide further information concerning the relations between the main domains of assessments. On top of contribution for our understanding of factors contributing to the within-subjects’ fluctuations in pain, if our hypothesis will be confirmed, measures of within-subjects variability could be used as a diagnostic method to promote individual pain medicine: by taking into consideration that higher within-subjects variability means that the patients lack of certainty in the ascending sensory information from the environment, these patients could benefit from interventions aimed at improving direction of attention towards the internal state of the body (e.g., meditation or yoga). On the other hand, patients who exhibit lower within-subjects variability could benefit most from psychological interventions aimed to target cognitive resources such as, modifying expectations, by boosting expectations for benefit from treatment (and or distraction from pain).