Neural Correlates of Inter-Individual Differences in Pain Processing Investigated by Functional Magnetic Resonance Imaging of the Entire Central Nervous System
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The experience of pain is a highly complex and personal experience, characterized by tremendous inter-individual variability. Pain perception can differ substantially across individuals due to many factors such as age, gender, genetics, cognition and emotionality etc. Some individuals are very sensitive to pain whereas others tolerate pain well. Athletes can play competitive sports even with significant injuries while other people feel tremendous pain while getting a flu shot. This phenomenon of inter-individual variability in pain responses has challenged scientists and clinicians alike. It is difficult to determine whether subjective reports of pain reflect true individual experiences of pain. However, the development of neuroimaging techniques has dramatically progressed our understanding of pain processing. This project investigated the neural correlates of inter-individual differences in pain responses in healthy individuals, by means of functional magnetic resonance imaging (fMRI) of the entire central nervous system. Twenty-healthy participants were asked to rate their pain following a noxious thermal stimulus, while undergoing functional MRI, and considerable inter-individual variability was observed. Results from this project demonstrated central mechanisms in the brain, brainstem and spinal cord that contribute to this variability. Participants that reported higher pain to the noxious stimulus showed greater fMRI responses in some brain, brainstem and spinal cord structures involved in processing the emotional, cognitive and motivational aspects of pain. This showed that the subjective reports of pain are a reliable indicator, and inter-individual differences in pain responses truly reflect variability in pain experience. It is expected that this knowledge will contribute to a better understanding of the neuronal processes, as well as substantial inter-individual variability observed in chronic neuropathic pain populations such as fibromyalgia, patients with spinal cord injuries etc.