Objective: Explore whether levodopa-induced dyskinesia (LID) and chorea share voluntary movement characteristics to better understand the mechanisms underlying these involuntary movements.

Background: We have recently demonstrated that human voluntary 3D upper-limb movements can be segmented into sub-movements within individual Cartesian planes that resemble optimized 1D point-to-point movements. Furthermore, we demonstrated that these sub-movements scale with the size of movement according to a 2/3 power law and that this was related to movement optimization during motor planning.

Methods: We analyzed 3D kinematic data that was collected while subjects with PD (N=10) and HD (N=20) were asked to stand with arms outstretched in front of them for 30s. Subjects with PD performed 6 trials each, while subjects with HD performed between 2 and 7 trials each (mean=4). Here, we focus on results obtained from movement of both hands, from all subjects. First, we low-pass filtered the time series to remove non-human noise. We then computed the movement of the hand in relation to the center of mass in x, y, and z. Then, we derived the velocity profiles for each of the axes and determined the time support by detecting the zero-crossing points of the velocity time series. We applied specific criteria to discard sub-movements that could not be detected reliably. We plotted the mean velocity value vs. the displacement for each sub-movement using a log-log scale so that the slope of the regression line fitting the data determined the scaling exponent.

Results: A total of 14 672 sub-movements were extracted from the data of subjects with PD presenting with LID. The scaling exponent observed for LID was 0.60. For chorea, we extracted 29 733 sub-movements. The scaling exponent observed for chorea was 0.66.

Conclusions: Results presented here demonstrate that both LID and chorea can be segmented into sub-movements within individual Cartesian planes. Furthermore, these sub-movements appear to scale with the size of movement according to a 2/3 power law, as do voluntary movements. This indicates that despite the different pathophysiology of LID and chorea, the motor output is optimized; suggesting that both lead to the involuntary release of planned voluntary movements.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-scaling-properties-of-chorea-and-levodopa-induced-dyskinesia-are-similar-to-voluntary-movements/