Impaired self-initiated task preparation during task switching in Parkinson's disease

Patients with Parkinson's disease (PD) typically show reduced performance in clinical tests involving cognitive control processes, presumably due to reduced availability of dopamine in striatofrontal neuronal circuits. Although task switching paradigms are considered as an ideal experimental measure of cognitive control, previous studies on task switching in PD have yielded ambiguous results, indicating that performance deficits depend on the specific task requirements. Among these, the aspect of self-initiated as opposed to externally triggered task preparation seems to play an important role, as evidenced by recent research. To address this topic, the present study investigated PD patients and age-matched controls (n=16) with a sequential switching task in which the upcoming task was predicted by two different types of cues. Firstly, every task was predicted by an external visual cue of varying utility (long versus short precuing interval). Additionally, the tasks were predictable on the basis of a fixed task sequence (AABB), which placed relatively higher demands on self-initiated task preparation. After considerable practice, the sequence was changed to random. Increased reaction times following sequence removal indicated prior use of the sequence in both groups. However, in contrast to healthy age-matched controls, PD patients did not learn to use the predictable task sequence to a greater extent when the utility of the visual task cue was low due to a short precuing interval. This finding is interpreted as evidence for a specific impairment in self-initiated as opposed to externally triggered task preparation.