Individual differences in the vicarious perception of pain

Vicarious pain refers to the processes and experiences that arise from observations of other people in pain. Due to the interpersonal and multi-modal nature of these processes, research into the field is highly relevant for a number of key concepts in social cognitive neuroscience, such as empathy, multi-sensory processing and social cognition. The dominant approach in the field has been to focus on normative samples with little focus being given to inter-individual differences. The discovery of a subsample of the population who report conscious experiences of pain when observing it, so called ‘mirror-pain responders’, presents a significant opportunity for developing our understanding of the neural processes and characteristics associated with vicarious pain. The present thesis aims to extend understanding of this group who appear to lie on an extreme end of a spectrum of vicarious pain perception. Although past research has highlighted this group and made some attempts to identify their prevalence, few formal attempts have been made to stringently discover the prevalence and identify the characteristics of their qualitative experience. As such, ARTICLE I developed a questionnaire, named the Vicarious Pain Questionnaire (VPQ), which characterises mirror-pain responders based on their subjective experiences of pain. The results showed a surprisingly high prevalence rate for the condition, ~30%. In addition through the use of a cluster analysis, the VPQ identified subgroups within mirror-pain responders, which included a group who experienced sensory and localised mirror-pain, and a group that experienced affective and generalised mirror-pain. ARTICLE I and ARTICLE II both aimed at assessing the neural basis for the experiences and successfully highlighted the role of hyperactivity in vicarious somatosensory processing, through the use of electrophysiological (EEG) neuro-markers for somatosensory processing (mu rhythm) and functional magnetic resonance imaging (fMRI) activation in the somatosensory cortex during pain observation. Additionally, these articles highlighted the role of self-other processing regions through the use of voxel-based morphometry (VBM) which revealed reduced grey-matter volume in the right temporo-parietal junction (rTPJ), and psycho-physiological interactions (PPI) of fMRI processing which revealed connectivity networks between pain matrix regions and self-other processing regions (rTPJ and dorsomedial prefrontal cortex (DMPFC)). Characteristics of the mirror-pain were further assessed in ARTICLE III which in a battery of behavioural and physiological tests were administered to mirror-pain responders and controls. This study showed abnormal autonomic nervous system processing for Affective/General mirror-pain responders and confirmed the link between the condition and questionnaire measures of empathy. Finally, ARTICLE IV failed to provide a causal link between self-other processing regions (rTPJ) and somatosensory activation in response to pain observations through the use of theta-burst transcranial magnetic stimulation (TMS) in non-responders. This calls into question the direct causality of neural mechanisms associated with self-other theories of mirror-pain. This thesis demonstrates the importance of studying inter-individual differences in vicarious pain by reporting a set questionnaire and neuroimaging results which contribute to debates in the field and raises questions for future research. This work, its implications, and contributions to the wider literature are reviewed in the DISCUSSION chapter.