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DOI: 10.1055/s-2008-1072908
Ballistic Movements are less impaired in Parkinson's Disease than Controlled Movements
Parkinson's disease (PD) is a slowly progressing neurodegenerative disorder that leads to characteristic motor symptoms such as tremor, rigidity and bradykinesia [1]. It has been shown that the basal ganglia play an important role in timing of movement [2]. However, the movements of PD patients under certain conditions are less impaired than one would expect. Improved movements can be triggered by external timing cues [3], by sensory cues, like, for example, auditory cues [4] or visual cues [5; 6]. It has been hypothesized that by timing movements externally the basal ganglia function for timing of movements is bypassed. In the presented work we study the performance of PD patients on and off medication and normal control subjects in two types of movements: A ballistic punch against a punching bag and a controlled movement, in which the punch had to be stopped before the bag was touched. The patients were instructed to perform all movements as fast as possible. The movements were recorded via a Zebris ultrasound device for three dimensional movement recording. Statistical data analysis was performed by student's t-test and a random intercept model.
Maximal angular velocity of the elbow joint was computed from the position signal of three markers (hand, elbow, shoulder) during both the controlled and the ballistic punch. Over all subjects, the ballistic movement was significantly faster than the controlled movement (p=0.004). Only in the patient group were significant differences between controlled and ballistic movements seen. In the control group we did not measure any significant differences between controlled and ballistic movements (Vball: 546 deg/s Vcontrol: 535 deg/s; p=0.16). The ratio of Vball to Vcontrol of 1.02 underlines that the maximum speed of both movements in normal control subjects was virtually the same. Patients in off-state performed the controlled movement significantly slower than the ballistic movement (Vball: 493 deg/s Vcontrol: 414 deg/s; p<0.0001). Even in the on-state no change in the significance of Vball vs. Vcontrol was seen, but the mean value of maximum speed in both movement types increased considerably (Vball: 526 deg/s Vcontrol: 475 deg/s; p<0.0001). The ratio of maximum speed of both movements reveals that the improvement is more pronounced in the controlled movement (ratio [on condition] Vball/Vcontrol =1.11; ratio [off condition] Vball/Vcontrol =1.19). This finding was confirmed by measurements of a second patient group that was treated with subthalamic nucleus deep brain stimulation for PD (ratio [on condition] Vball/Vcontrol =1.14; ratio [off condition] Vball/Vcontrol =1.24). We conclude that the overall movements are facilitated effectively by dopaminergic treatment. The finding that the controlled movement is considerably slower than the simple ballistic movement in PD patients leads us to conclude that slowness of movement is unequally more pronounced for complex as compared to simple movements in these patients.
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