The basal ganglia are a group of interconnected subcortical nuclei — the striatum (caudate nucleus and putamen), globus pallidus, subthalamic nucleus, and substantia nigra — that play critical roles in action selection, procedural learning, habit formation, and reward processing. They receive input from the entire cortex and project (via the thalamus) primarily to the frontal cortex, forming cortico-basal ganglia-thalamocortical loops.
Functions in Cognition
The basal ganglia contribute to cognition through several mechanisms. In procedural learning, the striatum gradually acquires stimulus-response associations through reinforcement, supporting the development of habits and skills. In action selection, the basal ganglia facilitate desired actions (through the direct pathway) while suppressing competing actions (through the indirect pathway). In reward processing, dopaminergic signals from the substantia nigra and ventral tegmental area encode reward prediction errors that drive learning.
Parkinson's disease (degeneration of dopaminergic neurons in the substantia nigra) produces motor and cognitive symptoms including slowed thinking, difficulty initiating actions, and impaired procedural learning. Huntington's disease (degeneration of medium spiny neurons in the striatum) produces a different pattern of cognitive impairment. These disorders provide natural experiments that reveal the cognitive functions of the basal ganglia.