The sight of others' pain modulates motor processing in human cingulate cortex.

Neuroimaging evidence has shown that a network including cingulate cortex and bilateral insula responds to both felt and seen pain. Of these, dorsal anterior cingulate and midcingulate areas are involved in preparing context-appropriate motor responses to painful situations, but it is unclear whether the same holds for observed pain. Participants in this functional magnetic resonance imaging study viewed short animations depicting a noxious implement (e.g., a sharp knife) or an innocuous implement (e.g., a butter knife) striking a person's hand. Participants were required to execute or suppress button-press responses depending on whether the implements hit or missed the hand. The combination of the implement's noxiousness and whether it contacted the hand strongly affected reaction times, with the fastest responses to noxious-hit trials. Blood oxygen level-dependent signal changes mirrored this behavioral interaction with increased activation during noxious-hit trials only in midcingulate, dorsal anterior, and dorsal posterior cingulate regions. Crucially, the activation in these cingulate regions also depended on whether the subject made an overt motor response to the event, linking their role in pain observation to their role in motor processing. This study also suggests a functional topography in medial premotor regions implicated in "pain empathy," with adjacent activations relating to pain-selective and motor-selective components, and their interaction.