Dopamine error signal to actively cope with lack of expected reward

To obtain more of a particular uncertain reward, animals must learn to actively overcome the lack of reward and adjust behavior to obtain it again. The neural mechanisms underlying such coping with reward omission remain unclear. Here, we developed a task in rats to monitor active behavioral switch toward the next reward after no reward. We found that some dopamine neurons in the ventral tegmental area exhibited increased responses to unexpected reward omission and decreased responses to unexpected reward, following the opposite responses of the well-known dopamine neurons that signal reward prediction error (RPE). The dopamine increase reflected in the nucleus accumbens correlated with behavioral adjustment to actively overcome unexpected no reward. We propose that these responses signal error to actively cope with lack of expected reward. The dopamine error signal thus cooperates with the RPE signal, enabling adaptive and robust pursuit of uncertain reward to ulti-mately obtain more reward.

Automated summary

Animals must learn to actively overcome reward omission and adjust behavior to obtain more uncertain rewards. The neural mechanisms underlying this coping with reward omission are still unclear. In this study, a task was developed in rats to monitor active behavioral switch after no reward. It was found that some dopamine neurons in the ventral tegmental area exhibited increased responses to unexpected reward omission and decreased responses to unexpected reward, opposite to the well-known reward prediction error signaling dopamine neurons. The dopamine increase in the nucleus accumbens correlated with behavioral adjustment to actively overcome no reward. These findings suggest that these responses signal error to actively cope with the lack of expected reward, enabling adaptive pursuit of uncertain reward to obtain more reward.