Putting oneself in the perspective of the other: a framework for self-other differentiation.

Self-other differentiation requires both that one can understand the actions others perform, and that one can attribute these actions to them. Understanding implies that a complete description of the actions of other agents can be available in the brain of the observer. Attributing implies that the agent can be clearly differentiated from the self. The model for the self-other differentiation proposed here can therefore involve two steps: I first displace myself at the location of the person I observe in order to specify her/his location in space. Then, I simulate the action I observe from that person in order to understand what she/he is doing. Assuming that the two operations are more or less synchronous, the action I simulate is automatically attributed to the person I observe, not to myself. The simulation network in the observer's brain overlaps with the execution network in the agent's brain; by contrast, the rotation network is specific to the observer's brain. In a neuroimaging experiment using PET, we compared brain activity during a task where the subjects simulated an action of grasping an object from either first-person or third-person perspectives. This comparison revealed an activation limited to the parieto-occipital junction (area 19), which appeared to be specific to the third-person perspective. The activation of this area is proposed to represent a cue for the self-other differentiation.