Fig. 4.

Hypothetical Roles for Dopamine. (A) The dopamine clock hypothesis. Under the dopamine clock hypothesis, high levels of dopamine cause the internal clock to speed up, which in turn causes the behavioral output to exhibit underestimation or overproduction depending on the task. (B) Dopamine signals reflect reward prediction errors, which are used to rescale the speed of the clock depending on whether the reward arrived earlier or later than expected. This would change the speed of the clock on subsequent trials with the goal of increasing temporal accuracy when predicting reward. (C) Dopamine signals reflect temporal prediction errors when external cues of time disagree with the internal clock. In this case, dopamine signals could adjust the position of the internal clock to agree with the external cues. (D) External timing cues compared with the output of the internal clock produce dopaminergic prediction errors that are then used to inform the behavioral output. (E) Dopamine signals inform the behavioral output by ramping to a threshold for action initiation. The level of dopamine activity encodes the temporal proximity to reward, which is informed by the internal clock.