Dissociation between spontaneous and reactive flexibility in early Parkinson's disease

Objective: This study was designed to examine the relations between the severity of motor symptoms and impaired cognitive flexibility in Parkinson's disease. Background: Studies that examine cognitive flexibility in Parkinson's disease report conflicting results. We hypothesized that such inconsistency may reflect a differential pattern of impairment on tasks that measure spontaneous versus reactive flexibility. Methods: The performance of tasks requiring either spontaneous (Alternate Uses) or reactive (Wisconsin Card Sorting Test) cognitive flexibility was examined in newly diagnosed unmedicated patients with idiopathic Parkinson's disease, as compared with age- and education-matched controls. The correlation between the degree of deficit and severity of motor symptoms was also examined. Results: Patients were significantly worse than controls in performing both types of tasks. The patients' performance on tasks of spontaneous reactivity was not correlated with the presence or severity of the motor signs and symptoms. However, only patients showing signs of bradykinesia were impaired on a measure of reactive cognitive flexibility and the degree of impairment was significantly correlated with the severity of bradykinesia. Conclusions: These findings suggest that the dissociation between the two types of cognitive flexibility may reflect the differential involvement of the mesocortical and striatonigral dopaminergic circuits in the mediation of these tasks.