Impact of specific executive functions on driving performance in people with Parkinson's disease.

Executive functions encompass various cognitive processes and are critical in novel or demanding driving situations. Our aim was to determine the role of impairments in specific executive functions (updating, flexibility, inhibition) on road performance in drivers with Parkinson's disease (PD), a condition commonly associated with early executive dysfunction. In this pilot study, 19 patients with mild to moderate PD and 21 healthy controls matched for age, education, and driving experience were tested using a neuropsychological battery assessing global cognitive abilities, updating (n-back task), flexibility (plus-minus task), and inhibition (Stroop test). Participants also underwent a 45-minute road test in which they were scored by a driving instructor and a second experimenter. To separate "at-risk" drivers from safe drivers, a composite driving indicator was calculated from the Test Ride for Investigating Practical Fitness to Drive score, the penalty score from the observation grid, and the number of safety interventions made by the driving instructor. Eight of the 40 drivers (all PD) were rated as "at risk." Measures of updating (the n-back task) and mental flexibility (the plus-minus task) predicted driving safety even after adjustment for group status, explaining 53% of the total variance. These 2 tests also discriminated between safe and "at-risk" drivers within the PD group. These findings, although preliminary, suggest that updating and mental flexibility are critical for safe driving in PD. Assessment batteries for driving fitness should probe different aspects of executive functions, specifically when evaluating drivers with PD.