title: Changes in Timing and kinematics of goal directed eye-hand movements in early-stage Parkinson's disease.
abstract: OBJECTIVE
  Many daily activities involve intrinsic or extrinsic goal-directed eye and hand movements. An extensive visuomotor coordination network including nigro-striatal pathways is required for efficient timing and positioning of eyes and hands. The aim of this study was to investigate how Parkinson's disease (PD) affects eye-hand coordination in tasks with different cognitive complexity.
  
  
  METHODS
  We used a touch screen, an eye-tracking device and a motion capturing system to quantify changes in eye-hand coordination in early-stage PD patients (H&Y < 2.5) and age-matched controls. Timing and kinematics of eye and hand were quantified in four eye-hand coordination tasks (pro-tapping, dual planning, anti-tapping and spatial memory task).
  
  
  RESULTS
  In the pro-tapping task, saccade initiation towards extrinsic goals was not impaired. However, in the dual planning and anti-tapping task initiation of saccades towards intrinsic goals was faster in PD patients. Hand movements were differently affected: initiation of the hand movement was only delayed in the pro-tapping and dual planning task. Overall, hand movements in PD patients were slower executed compared to controls.
  
  
  CONCLUSIONS
  Whereas initiation of saccades in an extrinsic goal-directed task (pro-tapping task) is not affected, early stage PD patients have difficulty in suppressing reflexive saccades towards extrinsic goals in tasks where the endpoint is an intrinsic goal (e.g. dual planning and anti-tapping task). This is specific for eye movements, as hand movements have delayed responses in the pro-tapping and dual planning task. This suggests that reported impairment of the dorsolateral prefrontal cortex in early-stage PD patients affects only inhibition of eye movements. We conclude that timing and kinematics of eye and hand movements in visuomotor tasks are affected in PD patients. This result may have clinical significance by providing a behavioral marker for the early diagnosis of PD.
authors.affiliation: Department of Neuroscience, Erasmus MC, PO Box 2040,, 3000, CA, Rotterdam, The Netherlands.
authors.forename: Danya
authors.initials: D
authors.lastname: Muilwijk
authors.affiliation: Department of Neuroscience, Erasmus MC, PO Box 2040,, 3000, CA, Rotterdam, The Netherlands.
authors.forename: Simone
authors.initials: S
authors.lastname: Verheij
authors.affiliation: Department of Neuroscience, Erasmus MC, PO Box 2040,, 3000, CA, Rotterdam, The Netherlands.
authors.forename: Johan Jm
authors.initials: JJ
authors.lastname: Pel
authors.affiliation: Department of Neurology, Erasmus MC, PO Box 2040, 3000, CA, Rotterdam, The Netherlands.
authors.forename: Agnita Jw
authors.initials: AJ
authors.lastname: Boon
authors.affiliation: Department of Neuroscience, Erasmus MC, PO Box 2040,, 3000, CA, Rotterdam, The Netherlands.
authors.forename: Johannes
authors.initials: J
authors.lastname: van der Steen