Aspects of procedural memory are differentially impaired in Huntington's disease

Procedural memory encompasses several phenomena, including motor and perceptual learning, cognitive rule learning and priming. These subclasses are differentially affected by differing neuropathologies, suggesting their functional independence and reliance upon different neural substrates. To test this hypothesis, performance on a maze learning task was compared in 15 Huntington's disease (HD) patients and 15 normal controls (NC) to assess specific route learning, cognitive skill learning and the effects of route predictability on performance. Results revealed that the HD group: (1) showed normal learning curves for a specific maze route; (2) are deficient in generalizing the cognitive skills across mazes; and, (3) fail to improve performance on a maze with a predictable route relative to mazes with unpredictable routes. These results are interpreted as supporting the independence of procedural memory subclasses. The basal ganglia are suggested as important structures in mediating the ability to generalize skills and appreciate patterned organization in to-be-acted-upon stimuli.