Extrinsic rewards, intrinsic rewards, and non-optimal behavior.

The optimality of behavior in experimental settings is usually determined with respect to an extrinsic reward defined by the experimenters. However, actions that do not lead to reward are ubiquitous in many species and in many experimental paradigms. Modern research on decision processes commonly treat non-optimal behaviors as noise, often excluding from analysis animals that do not reach behavioral performance criteria. However, non-optimal behaviors can be a window on important brain processes. Here we explore the evidence that non-optimal behaviors are the consequence of intrinsically motivated actions, related to drives that are different from that of obtaining extrinsic reward. One way of operationally characterizing these drives is by postulating intrinsic rewards associated with them. Behaviors that are apparently non-optimal can be interpreted as the consequence of optimal decisions whose goal is to optimize a combination of intrinsic and extrinsic rewards. We review intrinsic rewards that have been discussed in the literature, and suggest ways of testing their existence and role in shaping animal behavior.