Ventral Striatal Neurons Encode the Value of the Chosen Action in Rats Deciding between Differently Delayed or Sized Rewards

The ventral striatum (VS) is thought to serve as a gateway whereby associative information from the amygdala and prefrontal regions can influence motor output to guide behavior. If VS mediates this "limbic-motor" interface, then one might expect neural correlates in VS to reflect this information. Specifically, neural activity should reflect the integration of motivational value with subsequent behavior. To test this prediction, we recorded from single units in VS while rats performed a choice task in which different odor cues indicated that reward was available on the left or on the right. The value of reward associated with a left or rightward movement was manipulated in separate blocks of trials by either varying the delay preceding reward delivery or by changing reward size. Rats' behavior was influenced by the value of the expected reward and the response required to obtain it, and activity in the majority of cue-responsive VS neurons reflected the integration of these two variables. Unlike similar cue-evoked activity reported previously in dopamine neurons, these correlates were only observed if the directional response was subsequently executed. Furthermore, activity was correlated with the speed at which the rats' executed the response. These results are consistent with the notion that VS serves to integrate information about the value of an expected reward with motor output during decision making.