Cognition and the basal ganglia: a possible substrate for procedural knowledge.

Disruption of neural activity within the basal ganglia of experimental animals causes selective learning deficits in tasks requiring switching between response strategies. These data along with reports of both general and specific intellectual impairment in patients with neurodegenerative disorders such as Parkinson's disease, appear to support the theory of cognitive functions of the basal ganglia. Recent studies have failed to confirm general cognitive or memory deficits in parkinsonian patients, but have identified deficiencies in devising and executing certain cognitive strategies. Following the lead of theorists such as Squire and Mishkin, this brief review emphasizes the distinction between procedural and declarative knowledge and examines the possible role of the basal ganglia in the acquisition and retention of procedural knowledge.