Behavioral neuroscience of human pain communication: The meaning of pain expression and vicarious pain responses

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Darwin's legacy includes a detailed description of the reliable behavioral patterns produced to communicate emotions and the proposal that such responses provide unique adaptive advantages to social species. In this context, the communication of pain constitutes a fundamental process that may have at least two distinct functions. First, pain expression signals potential threats in the immediate environment of the bystanders (i.e. vicarious pain signals) and may allow them to predict and anticipate potential harm, prevent and avoid self-exposure to the source of nociception, and/or trigger or facilitate self-defensive or protective responses to reduce the risk or the extent of injury. The second function of pain communication concerns the elicitation of solicitous behaviours with the corollary assumption that these may reduce the risk of further injury and/or the suffering of the person expressing pain. Based on communication models one can distinguish three phases in this process reflecting the encoding or « communication as action », decoding or « communication as interaction », and the ensuing social regulatory processes or « communication as transaction ». In neuropsychological terms, encoding involves the activation of a representation of pain triggered by a painful event and expressed or « encoded » in various output channels including facial expression. Decoding requires the perception of vicarious pain signals and is thought to involve the activation in the observer of a partly shared neural/mental representation of the nociceptive event and the corresponding pain state. Finally, transaction reflects the potential impact of the information exchanged on the observer and the expresser's neurophysiological and psychological state. Here, we propose to explore the neural mechanisms underlying these three stages of pain communication using experimental approaches, psychophysiology and functional brain imaging in healthy human.