EFFECTS OF CHANGES IN RESPONSE EXPECTANCY ON PAIN PERCEPTION AND ELECTROPHYSIOLOGY

Access to files

•   FULL-TEXT.PDF (pdf)

Abstract

Clinical evidence suggests that a negative expectancy of pain decreases the effectiveness of interventions aimed to reduce pain. Experimental pain models provide a method to investigate neurophysiological and psychological correlates of sensory processing and decision-making of clinically observed phenomena in the context of pain. The purpose of this thesis was to develop an experimental paradigm to investigate the neural and psychological mechanisms of the distorting effect of negative expectancy on pain-reducing predictive cues, the latter of which is thought to be the underling mechanism of all effective treatments for pain. Chapter One lays the foundation required to understand the thesis: it introduces the current direction as well as the expanding research in the field of physiological, psychological, and imaging pain research. The reviewed literature and identified knowledge gaps sculpt the aims, objectives, and justification of this PhD research. Chapter Two discusses the technical aspects that allow translating the theoretical concepts addressed in Chapter One into experimental settings; in this chapter, commonly used methods to induce and image pain, as well as behavioural assessment measures, are discussed. A brief preview on the most recent state-of-the-art technology in neuroscience imaging is also provided. Chapter Three provides a thorough description of the two pilot studies that were conducted to develop a suitable experimental paradigm to investigate the impact of prior negative expectations on pain-reducing predictive cues, using a laser-heat as a pain model. The pilot work provides experimental justification for the final paradigm that was implemented in subsequent studies. Electroencephalography (EEG) was used to probe the neural and cognitive mechanisms underlying the expectancy modulation of pain. In Chapter Four, the main hypothesis that the experimental induction of negative expectations indeed reduces the pain-alleviating effect of predictors of a non-painful outcome was examined. As hypothesised, participants reported laser stimuli as more painful in the context of prior negative expectations. Furthermore, participants had higher amplitudes of the N2 peak of the laser evoked potential in this context. This N2 difference was correlated with the activation of the midcingulate cortex (MCC). Results also revealed a positive correlation between participants’ self-rated scores on the fear-of-pain questionnaire (FPQ) and the enhanced N2. This suggests a priming effect may have occurred through the increased recruitment of saliency mechanisms at pre-evaluative stages of sensory processing, to which fearful individuals were more prone to. Chapter Five takes this finding a step further by modulating pain catastrophising in the anticipation that individuals who are classified as high-pain catastrophisers would be more prone to the prior negative expectancy effect, as well as more responsive to an intervention designed to minimise it, which, in the study, was a sensory-focusing task designed to take attention away from catastrophic thinking. Results, however, showed that both groups reported equally higher intensity ratings in the prior negative expectancy condition, which were equivalently attenuated by the localisation task. Interestingly, the localisation task selectively increased the amplitude of P2 peak under prior negative expectancy trials. This effect was associated with the activation of the right orbitofrontal cortex (OFC) and secondary somatosensory cortex (SII), highlighting these regions’ role in the integration of motivational and cognitive components of pain to shape subsequent behavioural responses. The final chapter presents a critical analysis of the thesis findings and highlights its limitations, the clinical and research significance, future work, and draws final conclusions. The findings from this PhD thesis stress the importance of considering the distorting effect of negative expectancies on pain in planning effective pain intervention protocols. It also sheds a light on the possible mechanisms that cause this effect.

Bibliographic metadata

Institutional metadata

Record metadata