Chapter 22 - Understanding Parkinson's disease pathophysiology: clinical application of eye movement tasks and underlying neural correlates

Abstract

Parkinson's disease (PD) impairs somatomotor and oculomotor systems. A moving object of interest induces smooth-tracking eye movements (i.e., smooth pursuit) in normal primates, but most PD patients exhibit steplike-tracking eye movements (saccadic pursuit). Basic features of smooth pursuit are well established. To understand the nature of impaired pursuit in PD, we first briefly review some features of smooth pursuit in normal primates including eye movement tasks and neural correlates. We then review recent results showing the specific nature of impaired pursuit in PD. By comparing the results with monkey data, we deduce underlying pathophysiology. We suggest that the frontal eye fields/basal ganglia loop, first suggested by Cui, Yan & Lynch (2003), is important for efficient and automatic smooth-pursuit performance and is dysfunctional in PD. We also suggest that some PD patients with difficulty in pursuit planning have dysfunction of cerebral-cerebellar networks including supplementary eye fields and cerebellar oculomotor vermis/caudal fastigial nuclei.