Hierarchical control of goal-directed action in the cortical-basal ganglia network

- A hierarchical control process mediates the performance of goal-directed actions.
- Goal-directed actions can be simple or complex configurations of simpler actions.
- The hierarchical controller chooses between the simple and complex actions.
- Hierarchical control is implemented in the cortical-basal ganglia network.
- Secondary motor area efferents to the striatum regulate actions and habits.

Goal-directed control depends on constructing a model of the world that maps actions onto specific outcomes, allowing choice to remain adaptive when the values of outcomes change. In complex environments, however, such models can become computationally unwieldy. One solution to this problem is to develop a hierarchical control structure within which more complex, or abstract, actions are built from simpler ones. Here we review findings suggesting that the acquisition, evaluation and execution of goal-directed actions accords well with predictions from hierarchical models. We describe recent evidence that hierarchical action control is implemented in a series of feedback loops integrating secondary motor areas with the basal ganglia and describe how such a structure not only overcomes issues of dimensionality, but also helps to explain the formation of actions sequences, action chunking and the relationship between goal-directed actions and habits.