Changes in sensorimotor function associated with the degree of bradykinesia of Parkinson's disease

Changes in coordinated eye and hand movements associated with the progress of bradykinesia were studied in 31 parkinsonian patients and 8 age-matched healthy subjects. Among the parameters expressing the changes in motor behaviour, the interval between the onset of eye and hand movements was most sensitive. This parameter reflected the difference in the progress of the symptom in the two motor systems. An increase in the reaction time of the hand response appeared in patients of grade II bradykinesia; this was observed for eye movements only in patients with grade III (severe) bradykinesia. While the changes in ocular reaction time remained within the physiological range, a lengthening of the reaction time, a reduction in peak velocity, a decrease in the open-loop gain, a prolongation of movement duration, and a slow build-up in EMG activity, appeared from an early stage in hand movement. These signs of motor disturbance may appear eventually in every motor system at an advanced stage, but their development is not synchronous in different motor systems. An analysis of the responses recorded simultaneously from the two motor systems examined made it possible to evaluate the changes in the sensorimotor processes with different grades of bradykinesia. A comparison between reaction times for eye and hand movements may be useful for assessing the degree of bradykinesia in parkinsonian patients.