New Type of Dopamine Signaling in Reward Pathways

It is well known that striatal dopamine neurons fire both in a tonic manner and in phases in response to immediate rewards. These activities, however, do not account for how dopamine release is related to distant rewards. To examine distant reward signaling, researchers placed voltage recording devices in the dorsolateral and ventromedial striata of nine rats, who were then trained to run mazes with distant rewards (chocolate milk). Rats were trained to navigate mazes of T, M, and S shapes, which enabled the examination of different running times and distances. Rewards alternated from right to left sides and varied from small to large amounts.

As expected, phasic increases in dopamine occurred when animals reached the reward. In addition to …