Modulating persistent pain with caloric vestibular stimulation and perceptual rivalry
2017-01-31T00:10:16Z (GMT) by
Persistent pain (PP) can contribute to a significant disease burden for many of its sufferers. For those with significant PP warranting health interventions, current treatment options may be expensive and invasive. Investigations of novel, non-invasive, methods of pain modulation could offer a new means of intervention and provide valuable information regarding the interaction of pain with other systems in the brain. Caloric vestibular stimulation (CVS) is one such method and describes the activation of the vestibular system via a thermal stimulus. The first aim of this thesis was to explore the extent of the effects of CVS in PP conditions, with a particular emphasis on pain modulation. Evidence regarding CVS effects and its influence on the brain is reviewed comprehensively. An in-depth investigation of CVS in PP was conducted, representing the first experimental trial of CVS in multiple pain populations. Participants comprised 14 patients with complex regional pain syndrome (CRPS), eight with phantom limb pain (PLP), 12 with spinal cord injury pain (SCIP) and four with non-specific persistent pain (NPP). Ratings of pain and associated symptoms were recorded pre- and post-CVS and pre- and post-control procedure. Modest but statistically significant reductions in subjective pain were reported in a variety of PP conditions relative to a control procedure. Substantial reductions of allodynia in CRPS were also reported. Randomised controlled trials (RCTs) of CVS are required to assess and optimise therapeutic efficacy. Another phenomenon that may influence pain is perceptual rivalry, which refers to stimuli that elicit perceptual alternations when continuously viewed, such as ambiguous figure rivalry (AFR) and binocular rivalry (BR). Complex regional pain syndrome has been reported to interact with AFR, such that experiencing perceptual alternations is associated with increasing pain levels, and that patients with CRPS have faster than normal switch rates. The second aim of this thesis was to determine whether perceptual rivalry could influence PP conditions, with a subsidiary aim of investigating the impact of PP on parameters of perceptual rivalry. Parameters of BR were examined in 20 participants with PP, including: PLP, NPP, fibromyalgia and CRPS. Twenty healthy individuals formed an age matched control group. In order to validate previous findings, AFR was also viewed. Subjective pain ratings were recorded if participants indicated experiencing a change in how they felt. Half of the participants also viewed a simulated rivalry condition to control for the cognitive and visual intensity of the task. Pain significantly increased in participants with PP during perceptual rivalry viewing compared to baseline and controls. While the perceptual alternation rate and the duration of mixed/unusual percepts did not differ between PP and control groups, participants with PP perceived horizontal gratings significantly more often during BR. The findings of this thesis indicate the validity of CVS and perceptual rivalry as methods of non-invasive pain modulation and highlight their potential utility in research and, in the case of CVS, therapeutic contexts.