Who's on first? What's on second? The time course of learning in corticostriatal systems.

The prefrontal cortex and basal ganglia are known to be crucial for learning arbitrary sensorimotor associations (e.g. knowing to stop at red traffic lights). However, little is known about the timing of learning-related activity in these brain systems. Conventional wisdom suggests that the prefrontal cortex should drive learning-related changes in the basal ganglia. However, it is possible that the basal ganglia are instead responsible for the development of learning-related activity in prefrontal cortex. Indeed, recent work using methods for recording in the prefrontal cortex and basal ganglia simultaneously suggests that learning-related activity emerges first in the basal ganglia. Here, these studies are reviewed and integrated with the known anatomy of corticostriatal connections. Testable hypotheses regarding corticostriatal interactions during learning are proposed.