Microstructure of Arm Movements in Parkinson's Disease

Primary investigators:
Natalia Dounskaia (Arizona State University, Department of Kinesiology), Charles Adler (Mayo Clinic, Neurology, Movement Disorders Division)

The goal of the present project is to obtain preliminary data in support of a new approach to specification of movement features in Parkinson’s disease (PD) that focuses on submovements during pointing movements of PD patients. The approach predicts that submovements are not homogeneous and that they emerge due to at least two factors, motion termination and regulation of pointing accuracy. Because movements of PD patients are known for abnormally frequent submovements, clarifying sources of submovements in movements of these patients is a promising approach to developing objective and robust pre-diagnostic procedures and methods for evaluation of disease severity level and medication effect.

The project started on 01/01/2006. Thus, achievements obtained during eight months of the project are reported here. To obtain preliminary data supporting the formulated hypothesis, we have performed the experiment described in the proposal. Two subject groups were tested, idiopathic PD patients and age-matched controls. Each group included twelve subjects. All subjects were right-handed. All subjects performed pointing movements in different directions. The role of motion termination in the submovement emergence was addressed by including pointing movements in two modes, discrete and reciprocal. The discrete mode requires movement from the initial position to the target and stopping there, and therefore, it includes both subtasks, accurate target achievement and termination of motion. A reciprocal movement includes motion from the initial position to the target and a return to the initial position without dwelling on the target. In this case, pointing requires accurate target achievement similar to the discrete mode but it does not require motion termination because acceleration is not nullified at the target and motion continues in the reversal direction. The influence of the accuracy requirements was assessed with manipulations of target size (small and large target). Movements were performed with the tip of the index finger sliding on a table surface. Movements were recorded with Optotrack 3D motion recording system.

At present, the project is at the stage of data analysis. The analyses include parsing of submovements in three types according to zero-crossings in the velocity (type I), acceleration (type II) or jerk (type III) profiles. Also, we are computing movement time, characteristics of the velocity profile, and incidence of submovements. We are comparing them between the two groups, two movement modes, and two target sizes with use of a 2 x 2 x 2 (Group x Mode x Size) ANOVA. We expect to fully complete the data analysis at the end of October, 2006. We will spend the remaining two months (November and December) for preparing a manuscript reporting obtained results.

The preliminary results confirm previous findings that PD patients produce more frequent submovements than age-matched controls. A novel finding is that motion termination caused specifically frequent submovements in PD patients whereas incidence of submovements associated with accuracy requirements was approximately equal between the two groups. These results will be used to apply to NIH for a 5-year RO1 grant. Also, a manuscript will be prepared that will present these results. The results will be presented at the annual meeting of the Society for Neuroscience in October, 2006.