Procedural Memory, Motor Skill and Degenerative Neurological Disease

Dissociations between different aspects of memory in patients with amnesic syndromes and various neurodegenerative diseases has led to a fundamental revision of the taxonomy of human memory, and a greater understanding of its neurobiological basis. Lesions to temporal and diencephalic structures, which severely disturb memory for factual information (‘declarative’ memory), leaves intact other aspects of learning and memory, e.g. priming, perceptual learning, cognitive skill acquisition and motor skill acquisition. The type of memory tapped by these tasks has been described as ‘implicit’ or ‘procedural’ memory A major stimulus to neuropsychological research over the past 10 years has been to find whether these aspects of learning and memory have their own neurological substrate. Attention has focused on implicit or procedural memory in patients with neurological diseases affecting the striatum. The evidence, however, argues against a single ‘procedural system’ based on the striatum. Rather, there appears to be a number of different systems each serving different aspects of non-declarative memory. This large body of research seems to have evolved without reference to the huge literature on skill, particularly motor skill, and associated areas of research. In particular, the models, paradigms and methods of analysis employed in ‘procedural’ research into skill have been extremely limited. Furthermore, the research has focused on the acquisition of new skills to the exclusion of the equally important area of the adaptability of existing skills. Recent evidence is provided on both of these aspects of skilled motor behaviour in patients with Parkinson’s disease. It is recommended that future research should adopt a more analytic approach and which utilise theory-driven methods to assess the processes of learning at different stages, rather than focus too much on broad classifications of behaviour such as procedural learning.