Predictive control of eye movements in Parkinson disease.

Four parkinsonian patients who had shown evidence of an impairment of predictive manual control and 4 age-matched normal subjects were tested for the predictive control of eye movements. Subjects tracked a target with their eyes as it moved in either irregular "noise" or regular (predictable) linear ramp or sine waveforms. Eye movements were monitored by electrooculography, and the overall tracking time lag for each condition was determined by cross-correlation. Both normal and parkinsonian subjects showed prediction in eye tracking on the regular waveforms (zero time lag or anticipation of the target track), indicating that (1) the parkinsonian loss of predictive control in manual tasks is not due to defective control of eye movements, and (2) there may be separate predictor mechanisms in the brain for eyes and hands.