Altruistic behaviors can be defined as those actions which are costly to self, beneficial to another, and do not convey a benefit from reputation or reciprocity on the part of the recipient. Behaviors which meet these criteria are widely observed in behavioral experiments utilizing the dictator game. It has been suggested altruists may receive direct utility in the form of "warm glow" which offsets the cost of their behavior. Alternatively, it has been suggested that social norms exist which supporting reciprocity and reputation, the salient features of those norms are reproduced in the experimental setting, and altruism will decrease over time as subjects gain experience in the experimental environment. We explore other-regarding behavior while subjects undergo functional magnetic resonance imaging in the context of a modified dictator game where money cost is either replaced or augmented with effort cost. We find behaviorally that subjects are willing to exert effort to benefit their counterpart, but will not expend money, even when the cost to the subject is trivial compared to the gains available to the counterpart. Neurologically, we find evidence that superior-temporal regions and temporo-parietal junction is active when subjects observe reward accruing to the counterpart but not to self. These regions are frequently implicated in theory of mind tasks where subjects must imagine the mental state of another individual, and in social contextual knowledge tasks, where subjects must access and utilize norms proscribing appropriate conduct in social settings. Our results suggest that regions of the brain associated with social knowledge and interaction are required to interpret those outcomes associated with other-regarding behavior, even in the context of a one-player game where social interaction is absent. This activation pattern is more consistent with a theory that other-regarding behavior is modulated by social norms than the "warm glow" of utility directly experienced from increased payments to the counterpart.