Don't look now or look away: Two sources of saccadic disinhibition in Parkinson's disease?

Recent studies found evidence of impaired inhibition of saccades (fast eye movements) in non-demented people with PD. It has been suggested that impaired eye movement control reflects a general deficit of automatic response inhibition associated with impaired cognitive function in Parkinson's disease (PD). This study investigated the nature and source of saccadic disinhibition in PD. Eighteen non-demented PD patients and 18 control subjects completed prosaccade ('look towards'), delayed ('wait for cue') and antisaccade tasks ('look away') and a number of neuropsychological tests. There was evidence of saccadic disinhibition and cognitive impairment in the PD group. In the eye movement tasks the PD group made more express saccades (very fast reflexive responses) in the prosaccade task with a gap, more timing errors in the delayed response task and more directional errors in the antisaccade task than the control group. On average, neuropsychological test scores for the PD group were lower than for the control group. Subjects in the PD group who made a large number of directional errors in the antisaccade task did not necessarily also make a large number of timing errors in the delayed response task. Timing error rates, but not directional error rates, were negatively associated with neuropsychological test scores. Higher directional error rates in the antisaccade tasks were associated with higher proportions of express saccades in prosaccade tasks. This pattern of results suggests that there is more than one source of saccadic disinhibition in PD. We conclude that evidence of saccadic disinhibition may not necessarily reflect a general deficit of automatic response inhibition and cognitive impairment in PD. (c) 2008 Elsevier Ltd. All rights reserved.