Pain is an unpleasant emotional experience. Similar to other emotions, pain also has a social dimension. People understand a person's suffering by observation of pain in his facial expressions. Research has shown that communication of pain signals does not end when the observer understand the observed person's feelings and it continues with the preparation an action by observer to respond to that specific situation. As a consequence, it is expected to have the observer's processing of information changed after observation of pain in another person. Vicarious pain modulation refers to the change in perceived pain in the observer after observation of pain in another person. In the current study, we investigated the cerebrospinal correlates of modulation of pain in the observer after observation of another person's painful facial expression. Subjects were scanned using a 3T MRI scanner (TIM Trio, Siemens; UNF-Montreal). During the scan, they received brief electrical stimulus at the sural nerve while they were observing dynamic emotional expressions (neutral/pain/fear). At the same time the EMG was recorded from the inner side of biceps femoris to have their nociceptive flexion reflex recorded. The NFR is a polysynaptic spinal reflex which its amplitude is known to be correlated with subjective pain experience and suggested to be an index of spinal processing of nociceptive signals. Results showed that observation of pain as compared to neutral expressions lead to stronger reflex and higher pain ratings. At the cerebral level, painful stimulation resulted in activation in the brain areas known to be involved in the processing of pain (e.g. Insula, ACC, ipsilateral somatosensory cortex). Observation of pain (compared to neutral) before the stimulation resulted in greater activation in the Insula and the mPFC. These findings are in line with the assumptions of the motivational priming model and earlier studies which suggested the facilitation of processing of negative information by suppression of processing of positive information when we face negative stimuli.
School of Cognitive Sciences, Institute for Research in Fundamental Sciences (IPM),
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