" in adults the anterior cingulate cortex activates when they see someone hurt. Ditto for the amygdala and insula, especially in instances of intentional harm—there is anger and disgust. PFC regions including the (emotional) vmPFC are on board. Observing physical pain (e.g., a finger being poked with a needle) produces a concrete, vicarious pattern: there is activation of the periaqueductal gray (PAG), a region central to your own pain perception, in parts of the sensory cortex receiving sensation from your own fingers, and in motor neurons that command your own fingers to move.fn3 You clench your fingers. "
― Robert M. Sapolsky , Behave: The Biology of Humans at Our Best and Worst