Brain responses to facial expressions of pain: emotional or motor mirroring?

The communication of pain requires the perception of pain-related signals and the extraction of their meaning and magnitude to infer the state of the expresser. Here, BOLD responses were measured in healthy volunteers while they evaluated the amount of pain expressed (pain task) or discriminated movements (movement task) in one-second video clips displaying facial expressions of various levels of pain. Regression analysis using subjects' ratings of pain confirmed the parametric response of several regions previously involved in the coding of self-pain, including the anterior cingulate cortex (ACC) and anterior insula (aINS), as well as areas implicated in action observation, and motor mirroring, such as the inferior frontal gyrus (IFG) and inferior parietal lobule (IPL). Furthermore, the pain task produced stronger activation in the ventral IFG, as well as in areas of the medial prefrontal cortex (mPFC) associated with social cognition and emotional mirroring, whereas stronger activation during the movement task predominated in the IPL. These results suggest that perception of the pain of another via facial expression recruits limbic regions involved in the coding of self-pain, prefrontal areas underlying social and emotional cognition (i.e. 'mentalizing'), and premotor and parietal areas involved in motor mirroring.