Dopamine ramps up

Abstract

We thought we had figured out dopamine, a neuromodulator involved in everything from learning to addiction. But the finding that dopamine levels ramp up as rats navigate to a reward may overthrow current theories. See Letter p.575 It has been suggested that when animals perform simple stimulus–response tasks, the phasic activity observed the in dopaminergic midbrain represents an expectation of immediately upcoming rewards. Ann Graybiel and colleagues now demonstrate a different form of reward-related dopamine signalling in the striatum. Using cyclic voltammetry, they observe prolonged dopamine signals in animals navigating mazes to obtain rewards. These responses steadily ramp up as animals approach their goals, and scale with both the distance and size of the rewards. These signals may represent motivational drive, and provide insight into the role of dopamine during extended goal-directed actions.