Intact encoding, impaired consolidation in procedural learning in Parkinson's disease.

Idiopathic Parkinson's disease (IPD) patients and matched healthy participants were compared on a non-motor procedural task involving semantically related inverted word pairs, and 3 months later to determine the extent of skill consolidation. IPD patients were found to acquire new procedural skills necessary to read these inverted words, thus indicating that they are not impaired in all types of procedural learning. However, results on post-tests 3 months later, revealed significant group differences with IPD subjects showing little off-line learning relative to the controls. This suggests that a dopamine (DA)-deafferented neural system is not consolidated in the same way that a normally DA-innervated system is, and that impaired maintenance of procedures and routines may place IPD patients in a situation of constant relearning of embedded strategies in motor and non-motor domains.