Effects of Mental Flexibility and Motor Dysfunction on Cognitive Performance in Patients With Parkinson's Disease

Background: Parkinson’s disease (PD) is a neurodegenerative disorder characterized by pervasive motor deficits, often accompanied by specific cognitive impairments, most prominently executive dysfunctions. However, it is often hard to determine whether the impaired performance of patients with PD on executive tests is the result of an executive dysfunction or whether it is due to motor difficulties. Objectives: The present study aimed to examine the relationship between cognitive inflexibility, an executive dysfunction consistently found in PD, and motor deficiencies in patients with PD using derived scores, from a common executive function test named trail making test (TMT). Patients and Methods: Fifty patients with PD and 50 demographically matched controls underwent neuropsychological examination which included TMT, part A and part B. Performance on each task was assessed and the following derived scores TMT B/A, TMT B-A/A, and TMT B-A were calculated and compared. Results: Mann-Whitney tests revealed significant group differences for the mean TMT A (P = 0.006) and TMT B (P = 0.000), which were both higher in the PD group, relative to controls. In addition, significant differences were found for one TMT product score (TMT B-A). Conclusions: The results presented a significantly lower performance of patients with PD compared to controls, indicating the presence of a mental flexibility impairment which is dissociable and independent from the motor dysfunction.