Preserved motor learning in Alzheimer's disease: implications for anatomy and behavior

Learning and retention of 3 types of information were examined in patients with Alzheimer's disease (AD) and in normal controls. While patients were unable to learn series of frequent words and unfamiliar faces, they improved significantly in a motor skill, showing a learning curve similar to controls. Furthermore, no significant loss of the motor skill was evident in a 20 min delay trial. Such dissociation in learning has not been noted previously in AD, although it has been noted in amnesias caused by other disease processes. The results support the existence of two, relatively independent, learning systems related to "declarative" knowledge and "procedural" knowledge. Judging from the pathologic correlates of these amnesias, the declarative knowledge system appears to be associated with corticotemporo/limbic structures, while the procedural system is likely to depend on corticocerebellar/striatal structures. The data also offer additional cognitive correlates for the selective damage to neural systems recently identified in AD.