An investigation of the emotional modulation of pain perception and neural processing in the human brainstem and spinal cord using functional magnetic resonance imaging

Abstract

Pain is an extremely subjective and complex sensory and emotional experience. It is affected by a range of factors including attention, suggestion, attitude, expectation, and affective state. The influence of emotion on pain perception and neural processing is the central focus of this thesis. Previous research has demonstrated that individuals exposed to a painful stimulus will rate that stimulus as more painful when accompanied by or associated with a negative emotional influence. Conversely, pain ratings decrease when the painful stimulus is coupled with a positive emotional influence. Although many studies have confirmed that emotional manipulations affect pain perception at a group level, there has been little exploration of the range in the effect size across individuals or the psychological characteristics that may act to mediate emotional modulation of pain. Furthermore, although there is a growing body of research exploring the neural response in the brain, no other study, to date, has used functional MRI to examine the neural response across the brainstem and spinal cord involved in emotional modulation of pain. As such, this thesis used a combination of behavioural measures and functional MRI to explore differences in the effect of emotional modulation on pain perception across individuals, along with the neural response in the brainstem and spinal cord. We observed a substantial degree of inter-subject variability for the emotional modulation of pain perception, along with significant correlations for scores on anxiety and depression questionnaires with the distinct effects for Positive and Negative emotional modulation of pain. Functional MRI results revealed an effect for emotional modulation of the neural response involved in pain processing in the ipsilateral dorsal horn of the spinal cord, along with several regions in the brainstem known to be involved in descending pain modulation. Functional connectivity of these areas was observed to vary based on the valence and arousal of the emotional stimuli. Therefore, the findings of this thesis provide novel insight into the subcortical neural network involved in emotional modulation of pain processing and the factors that influence the effect of emotions on pain perception.