Pain relief as an opponent process: a psychophysical investigation

Authors

  • Siri Leknes,

    1. Oxford Centre for Functional MRI of the Brain, Clinical Neurology and Nuffield Department of Anaesthetics, Oxford University, John Radcliffe Hospital, Oxford, UK
    2. Department of Physiology, Anatomy and Genetics, Oxford University, Oxford, UK
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    • *

      Present address: Cognitive Developmental Research Unit (EKUP), Department of Psychology, University of Oslo, Norway.

  • Jonathan C. W. Brooks,

    1. Oxford Centre for Functional MRI of the Brain, Clinical Neurology and Nuffield Department of Anaesthetics, Oxford University, John Radcliffe Hospital, Oxford, UK
    2. Department of Physiology, Anatomy and Genetics, Oxford University, Oxford, UK
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  • Katja Wiech,

    1. Oxford Centre for Functional MRI of the Brain, Clinical Neurology and Nuffield Department of Anaesthetics, Oxford University, John Radcliffe Hospital, Oxford, UK
    2. Department of Physiology, Anatomy and Genetics, Oxford University, Oxford, UK
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  • Irene Tracey

    1. Oxford Centre for Functional MRI of the Brain, Clinical Neurology and Nuffield Department of Anaesthetics, Oxford University, John Radcliffe Hospital, Oxford, UK
    2. Department of Physiology, Anatomy and Genetics, Oxford University, Oxford, UK
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Dr Siri Leknes, at *present address below.
E-mail: siri.leknes@psykologi.uio.no

Abstract

Relief from pain in humans is frequently measured by computing the reduction on an 11-point pain intensity scale. However, this definition of relief may be insufficient to capture the utility of pain relief for the individual. Based on pain literature and evidence from studies examining relief and reward, it is clear that pain relief is a broad concept comprising several factors, only one of which is pain intensity reduction. According to opponent process theory, all sensations consist of a primary process and a slow ‘opponent process’ of opposite valence, the purpose of which is to reduce the deviation from homeostatic balance. Here, opponent process theory provided a framework to explore the interaction between pain, relief and reward. We devised three psychophysical studies examining the temporal (Experiment I) and magnitude (Experiments I and II) relationships between pain severity and its subsequent relief. In Experiment III, we further manipulated the magnitude and pleasantness of relief experienced by applying innocuous cooling following noxious heat stimulation of capsaicin-sensitized skin. Results confirmed predictions from opponent process theory and showed that pain intensity reduction was significantly stronger than relief intensity ratings. Furthermore, continuous relief ratings appeared to reflect the speed of pain intensity reduction. Varying pain intensity parametrically confirmed that relief increases with pain intensity. That innocuous cooling following primary hyperalgesia intervention significantly increased the intensity, pleasantness and duration of relief provides further evidence that pain relief encapsulates more than a reduction in pain intensity. Importantly, the high relief pleasantness ratings confirmed the hypothesized link between relief and reward.

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