Procedural learning and neostriatal dysfunction in man.

Patients with early stage Parkinson's disease are shown to be selectively impaired in a cognitive task of procedural learning while remaining intact in recall and recognition tests of declarative memory. In contrast, amnestic patients showed the opposite set of deficits, thus demonstrating a double dissociation. Patients with early Huntington's disease were either comparable to the parkinsonian patients or to amnestics. In the advanced Huntington's group, both procedural learning and declarative memory were impaired. It is argued that cognitive procedural learning depends on the establishment of heuristic strategies through the action of a circuit which involves the neostriatum and the prefrontal cortex.