The ability to attribute mental states to others and understand the basis of their decisions is essential for human social interaction. A controversial theory states that this is achieved by simulating another's information processing in one's own neural circuits. The anterior cingulate cortex (ACC) is known to play an important role in the registration of discrepancies between the predicted and actual outcomes of decisions (prediction errors).When positive and negative feedback fails altogether, the failure may also signal errors in the prediction that the outcome of that decision would be informative and guide future decisions. Does the ACC signal that an outcome is unexpectedly uninformative? When an outcome directed to others is uninformative, do we understand their mental states by simulating them in the circuits of the ACC in our own brain? The aim of our study was to test for these two possibilities in the human brain with event-related fMRI. We tested whether the ACC processes errors in the prediction of informative feedback and whether the ACC is also activated when scanned subjects process the same outcomes of another's decisions. We show that each is processed by a separate subregion of the ACC.