Implicit memory in parkinsonian patients: evidence for deficient skill learning

The aim of this study was to investigate procedural learning in idiopathic Parkinson's disease (PD) patients. For this purpose, 18 nondemented PD patients and 20 age-matched healthy subjects were trained to learn a visuoperceptual skill (mirror reading) and a cognitive skill with a motor demand (puzzle assembly task). In 3-day sessions, the patients were requested to perform with repeated and unrepeated stimuli, in order to distinguish between pure procedural learning and skill learning at least partially supported by explicit memory retrieval. In the mirror reading task, the PD patients showed normal improvement in reading times for repeated words but no improvement at all for unrepeated stimuli. In the puzzle assembly task, PD patients did not show any significant learning either for repeated or unrepeated stimuli. These results, which document deficient learning of procedures in parkinsonians, are discussed in the light of conflicting data reported regarding implicit memory in PD.