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Title: Pain, pleasure and relief
Author: Leknes, Siri
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2008
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Abstract:
Pain and pleasure have historically been considered opposites, and appear to have mutually inhibitory effects. The aim of this thesis was to investigate the relationships between pain, pleasure and relief, both in terms of affect and in terms of the neural processing underpinning these sensations and their interactions. To this end, three psychophysical and four functional magnetic resonance imaging (fMRI) studies were conducted. The first study investigated the neural underpinnings of itch and motivation for relief. The results demonstrated the involvement of a network of regions previously implicated in sensory and motivational structures, highlighting the perhaps inextricable link between an unpleasant sensation and the desire for relief. The next three studies formed a senes ofpsychophysical investigations aiming to characterize the sensation of relief from brief thermal heat pain, and testing a number ofpredictions from the opponent process theory about relief. The behavioural measures of relief from these experiments showed a strong resemblance to the opponent process ofpain. The next study investigated the effects of anticipatory pleasure on pain processing. Anticipatory pleasure was induced via expectation of immediate cooling relief following noxious thermal stimulation, and results from physiological and fMRI data supported the hypothesis that anticipatory pleasure would reduce pain. The third fMRI experiment reported here investigated the relationship between relief and pleasure processing in the brain. Relief was induced via a safety cue following a 50% predictive pain cue. To allow for the comparison between relief and more classical reward processing, subjects imagined pleasant and neutral scenarios. Results showed some differences but also important similarities in relief and pleasure processing, notably in the medial prefrontal cortex and ventral striatum, where activation correlated with reported pleasantness. The final study reported here used fMRI to investigate the neural substrates ofpleasant pain. A moderate pain stimulus was presented in two different contexts. In one context, the alternative outcome was intensely painful, such that moderate pain caused relief; this stimulus was rated as pleasant during the experiment. In the other context, the moderate pain represented the worst outcome, and was rated as painful. Significant differences between the two (identical) moderate thermal stimuli were found in ratings of sensation and affect, as well as in arousal and activation in medial orbitofrontal cortex and amygdala. These brain regions appear to be involved when a painful sensation is transformed into pleasure. Overall, the results reported in this thesis demonstrated a strong link between relief from pain and pleasure. These findings support the notion that pain and pleasure are opposites and mutually inhibitory in some contexts, but as demonstrated by the co-occurrence of pain and pleasure in the last study reported here, the relationship between pain, pleasure and the resulting hedonic perception is complex. As recognised by Bentham more than two centuries ago, pain and pleasure are the two 'masters of mankind.' The results from this thesis suggest that as we move into a new era of neuroscientific research, the hedonic aspects ofpain and pleasure should be revisited, and their complementary natures explored further.
Supervisor: Not available Sponsor: Not available
Qualification Name: University of Oxford, 2008 Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.491178  DOI: Not available
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