Declarative and procedural learning in Parkinson's disease patients having tremor or bradykinesia as the predominant symptom

The distinction between procedural and declarative memory is widely accepted in the memory literature. Converging evidence makes a strong case that the medial aspects of the temporal lobes and the diencephalon subserve the declarative memory system. However, the neuroanatomy of procedural memory is much less clear. In animal studies, damage to the basal ganglia has been found to affect procedural memory, but studies of patients suffering from degenerative diseases of the basal ganglia (e.g., Parkinson's and Huntington's disease) are less conclusive. Two groups of Parkinson's disease subtypes, with tremor (PDt) and bradykinesia (PDb) as the predominant motor symptom, were compared to controls on declarative and procedural memory tasks. The two patient groups did not differ from each other on the declarative tasks. However, in the procedural learning tasks, the PDb but not the PDt group, was significantly impaired compared to the control group. The results are discussed in terms of the differential involvement of discrete neuroanatomic loops connecting the basal ganglia and the prefrontal cortex.