MSc by Research: The Effects of Exercise and Conditioned Pain Modulation (CPM) on Human Pain Perception: a study using EEG analyses and Quantitative Sensory Testing.

Introduction & Background
Chronic pain afflicts a significant proportion of individuals many of whom receive inadequate pain relief. It is imperative that new treatments are developed and human models of pain are increasingly used to better understand clinical pain. There is a view that a personalized approach to the clinical treatment of chronic pain will eventually supersede the current one-size-fits-all analgesic ladder pain management paradigm. Conditioned Pain Modulation (CPM) is a recently explored physiological paradigm focused around the “pain inhibits pain” phenomenon. CPM provides an indirect way to measure an individual’s endogenous analgesic capability; how able they are to modify and inhibit the transmission and perception of their own pain. There is a view that an individual’s pre-disposition to pain chronicity is linked to their pain resilience (or lack thereof) and this is correlated with their ability to generate CPM. A better understanding of this may help identify those most at risk of developing chronic pain. Targeting and enhancing these endogenous mechanisms underlying CPM has the potential to alleviate chronic pain relief, at least for a subset of the population (those with a strong “pro-nociceptive” phenotype).

Aim of study - The research project shall aim to establish a correlative relationship between a subject’s capacity to induce CPM and the manifestation of hypoalgesia in response to exercise. These factors will be considered in the context of potentially related personality traits e.g. degree of catastrophizing vs resilience. Understanding this relationship can potentially facilitate effective personalized chronic pain treatment for individuals who express to varying degrees an anti- or pro-nociceptive profile

Methodology & Experimental Approach
CHEPS & EEG - The research project aims to extend our understanding of CPM, through utilisation of Contact Heat Evoked Potential Stimulation (CHEPS) to stimulate the subject’s skin, and an electroencephalogram (EEG) to monitor the amplitude and latency of the Evoked Potentials produced in response to the noxious stimulation. The use of EEG and CHEPs is a relatively new technique which can give an objective measure of the subject’s pain processing by production and analysis of evoked potentials. The CHEPs technique uses a heating thermo-foil to deliver a pulse of heat to the skin at a range of innocuous and nociceptive temperatures. This produces a cortical evoked potential (EP) which can be measured via EEG to record summated potentials from neurones in the brain. The amplitude and latency of the EP can be used to provide objective and quantitative data relating to the subject’s pain processing.

CPM & Exercise – CPM can be induced in human subjects using several simple strategies but the most common is through the so-called thermal--pressor test where the subject immerses either a hand or foot into hot or cold water. This has the effect of modifying a subject’s pain ratings in response to pain stimuli applied to other areas of skin. CPM appears to be quite variable across populations though few systematic studies have fully characterized the CPM phenotype and even fewer have used CHEPS to objectively measure CPM. This protocol provides direct, quantifiable measurements of the subject perception of pain, enabling close examination of the efficacy of CPM. Published data has indicated profound similarities and a potentially causative relationship between CPM and exercise-induced hypoalgesia. Through utilisation of CHEPS, EEG and exercise protocols, the project would compare characteristics of exercise-induced hypoalgesia and CPM, to determine if the two phenomena are correlated and the level of subject variability. Finally, CPM is a complex, process, subject to both physiological and psychological influences. Certain psychological behaviours and personality traits (such as catastrophising and harm-avoidance) have been shown to predict the maximal magnitude of CPM induced by the participants. This will be studied in the current project.