Attention shifting in Parkinson's disease: an analysis of behavioral and cortical responses.

OBJECTIVE The study was designed to examine persistent (input selection) versus transient (input shifting) mechanisms of attention control in Parkinson's disease (PD). METHOD The study identifies behavioral and neural markers of selective control and shifting control using a novel combination of a flanker task with an attentional set-shifting task, and it compares patients with PD with matched controls. Event-related brain potentials (ERPs) were recorded, and analyses focused on frontally distributed N2 waves, parietally distributed P3 waves, and error-related negativities (Ne/ERN). RESULTS Controls showed robust shifting costs (prolonged response times), but patients with PD did not show evidence for comparable shifting costs. Patients with PD made more errors than controls when required to shift between attentional sets, but also when they had to initially maintain an attentional set. At the neural level it was found that contrary to controls, patients with PD did not display any N2 and P3 augmentations on shift trials. Patients with PD further did not display any error-related activity or posterror N2 augmentation. CONCLUSIONS Our results reveal that intact selective control and disrupted shifting control are dissociable in patients with PD, but additional work is required to dissect the proportionate effects of disease and treatment on shifting control in PD. Our ERP-based approach opens a new window onto an understanding of motor and cognitive flexibility that seems to be associated with the dopaminergic innervation of cortico-striatal loops.