Inhibitory control and spatial working memory in Parkinson's disease.

Patients with Parkinson's disease (PD) have difficulty performing tasks relying on inhibitory control and working memory, functions of the prefrontal cortex. Eye movement paradigms can be used to investigate basic sensorimotor functions and higher order cognitive aspects of motor control. This study investigated inhibitory control and spatial working memory in the saccadic system of 13 individuals with mild-moderate PD and 13 age-matched controls. Tasks explored suppression of reflexive saccades during qualitatively different tasks, generation of express and anticipatory saccades, and the ability to respond to occasional, unpredictable ("oddball") targets that occurred during a sequence of well-learned, reciprocating saccades between horizontal targets. Spatial working memory was assessed using single and two-step (involving a visually guided saccade during the delay period) memory-guided tasks. Results for the PD group indicated an increased percentage of response selection errors during an oddball task, reduced suppression of inappropriate reflexive saccades during memory-guided tasks (but not during fixation or saccade-engagement tasks), and an increased percentage of express and anticipatory saccades. Spatial working memory was preserved in the PD group during single and two-step memory-guided tasks. These findings are consistent with dysfunction within fronto-striatal and prefrontal-collicular pathways influencing suppression and selection of eye movements.