Objective: In this study, we compared kinematic parameters of reaching task between SCA12 and healthy control participants using a novel tracking device.

Background: Reaching for objects, one of the common abnormalities observed in movement disorder patients. Multiple brain areas are critical in directing coordinated reaching movement. Trained clinical eye can help to identify anatomical substrate by seeing reaching trajectory. We translated this clinical observation from bedside back to bench in SCA12 patients.

Method: For reaching task, participants sat in front of a custom-made device in a quiet, comfortable, and semi-illuminated room. The device has five transparent illuminating buttons placed at four corners and center of a plus maze. The peripheral buttons illuminate randomly separated by illumination of the central button. Each button illuminates 20 times with an interval between two consecutive illumination of 2 sec. The device is programmed through Raspberry Pi based system. Participants were instructed to press the button rapidly once they are illuminated. A digital camera recorded the movement from the top. The captured video was then processed in DeepLabCut (DLC) platform to generate a CSV file of estimated pixel locations of the annotated point on the dorsal surface of the middle finger. This output was then processed through a customized MatLab script.

Results: We compared reaching kinematic parameters of 16 SCA12 and 20 healthy participants. We found that maximum displacement from straight line connecting peripheral targets from center and variability of reaching trajectory were significantly higher in patients than control. Maximum speed of reaching does not differ between SCA12 and healthy participants. The end point precision of landing on the target and time fraction of peak speed were significantly reduced in patients. We found correlation of CAG repeats length with endpoint precision of landing at lateral direction and supination/pronation score with maximum speed of reaching at anterior direction.

Conclusion: Variability of reaching trajectory, maximum displacement from straight line connecting peripheral targets from center, end point precision of landing, and time fraction of peak speed are affected in SCA12 patients, suggestive of cerebellar and striatal involvement. These parameters may be used for objective estimation of upper limb motor control in patients with cerebellar involvement.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/reaching-kinematics-in-movement-disorder-patients-using-an-open-source-computer-vision-technology/