SUMMARY Midbrain dopamine neurons are well known for their strong responses to rewards and their critical role in positive motivation. It has become increasingly clear, however, that dopamine neurons also transmit signals related to salient but non-rewarding experiences such as aversive and alerting events. Here we review recent advances in understanding the reward and non-reward functions of dopamine. Based on this data, we propose that dopamine neurons come in multiple types that are connected with distinct brain networks and have distinct roles in motivational control. Some dopamine neurons encode motivational value, supporting brain networks for seeking, evaluation, and value learning. Others encode motivational salience, supporting brain networks for orienting, cognition, and general motivation. Both types of dopamine neurons are augmented by an alerting signal involved in rapid detection of potentially important sensory cues. We hypothesize that these dopaminergic pathways for value, salience, and alerting cooperate to support adaptive behavior.

SUMMARY The desire to know what the future holds is a powerful motivator in everyday life, but it is unknown how this desire is created by neurons in the brain. Here we show that when macaque monkeys are offered a water reward of variable magnitude, they seek advance information about its size. Furthermore, the same midbrain dopamine neurons that signal the expected amount of water also signal the expectation of information, in a manner that is correlated with the strength of the animal’s preference. Our data shows that single dopamine neurons process both primitive and cognitive rewards, and suggests that current theories of reward-seeking must be revised to include information-seeking.

SignificanceHumans desire to know what the future holds. Yet, at times they decide to remain ignorant (e.g., reject medical screenings). These decisions have important societal implications in domains ranging from health to finance. We show how the opportunity to gain information is valued and explain why knowledge is not always preferred. Specifically, the mesolimbic reward circuitry selectively treats the opportunity to gain knowledge about favorable, but not unfavorable, outcomes as a reward to be approached. This coding predicts biased information seeking: Participants choose knowledge about future desirable outcomes more than about undesirable ones, vice versa for ignorance, and are willing to pay for both. This work demonstrates a role for valence in how the human brain values knowledge.