Investigation of set-shifting ability in patients with Parkinson's disease: influence of task sequence type

Background: The aim of the present study was to investigate the origin of set-shifting deficits observed in Parkinson's disease (PD).

Methods: Seventeen patients diagnosed as having idiopathic PD were compared with 15 control subjects. We used a task-switching paradigm, including two tasks (task A and task B) so that subjects were required to switch either immediately after a switch-trial (i.e. alternating switch or ABA task sequence) or following one or two non-switch trials (ABBA or ABBBA task sequences).

Results: In both groups, switch cost (SC) in ABA task sequence was larger than SC in ABBA task sequence (p<0.05) and SC was larger in ABBA than ABBBA task sequence (p<0.05). PD patients demonstrated an increased SC compared to controls for alternating switch trials (p<0.01). Alternatively, when required to switch to a task abandoned two or three trials earlier (i.e. ABBA and ABBBA tasks sequences), patients did not demonstrate increased SC compared to controls.

Conclusions: The fact that SC associated with alternating switch trials was exacerbated in PD patients may reflect difficulties for switching to a recently inhibited task-set. In conclusion, our results indicate that set-shifting deficits in PD patients may depend of the type of task sequence.