Dimensions of Executive Function in Parkinson’s Disease

Background: Executive impairment is common in Parkinson’s disease (PD). However, it is unknown which dimensions of executive function are assessed by commonly used neuropsychological instruments and if clinical correlates of specific dimensions exist. Method: A convenience sample of 46 PD patients was evaluated with three executive function tests: the Tower of London-Drexel, the Trail-Making Test and the Stroop Color-Word Test. Factor analysis was used to probe for dimensions of executive control, and linear regression models were used to explore the association between the generated factors and other clinical features. Results: Factor analysis revealed two executive factors, one related to planning (eigenvalue = 4.2) and the other to inhibitory control (eigenvalue = 1.8), together accounting for 75% of the variance in scores. In linear regression models, poorer planning was associated with increasing severity of apathy (t = 2.11, p = 0.041), and diminished inhibitory control was associated with increasing severity of parkinsonism (t = 2.78, p = 0.008) and lower educational level (t = –2.23, p = 0.032). Conclusions: Planning deficits and diminished inhibitory control are two dimensions of executive impairment in PD, the former associated with decreased motivation and the latter with increased motor slowing. Similar performance on both executive and non-executive components of these instruments suggests that results of executive testing in PD may be confounded by non-executive deficits.