Practice Effects on Motor Control in Healthy Seniors and Patients with Mild Cognitive Impairment and Alzheimer's Disease

ABSTRACT

This research was designed to test the hypothesis that motor practice can enhance the capabilities of motor control in healthy controls (NC) and patients with a diagnosis of probable Alzheimer's disease (AD) and mild cognitive impairment (MCI), and consequently results in better motor performance. Approximately half of the subjects in the NC (n = 31), AD (n = 28), and MCI (n = 29) either received or did not receive practice on a task of fast and accurate arm movement with a digitizer. Changes in movement time (MT), movement smoothness (jerk), and percentage of primary submovement (PPS) were recorded and compared among the three groups across six blocks of trials (baseline and five training sessions). For all subjects, practice improved motor functions as reflected by faster and smoother motor execution, as well as a greater proportion of programming control. Compared to unaffected matched controls, AD and MCI subjects exhibited a greater reduction in movement jerk due to practice. Movement time and PPS data revealed that motor practice appeared to reduce the use of “on-line” correction adopted by the AD or MCI patients while performing the aiming movements. Evidently, their arm movements were quicker, smoother, and temporally more consistent than their untrained peers. The findings of this study shed light on how MCI and AD may affect motor control mechanisms, and suggest possible therapeutic interventions aimed at improving motor functioning in these impaired individuals.

ACKNOWLEDGMENTS

The authors thank the Alzheimer's Association for the support of this research (NIRG-02–3875). The authors also thank the Alzheimer's and MCI patients, their families, and the elderly participants for their willingness to participate and cooperate. In addition, appreciation is extended to Amanda S. Harris, who assisted with data collection, and Hans-Leo Teulings for his assistance in data collection and analyses.

Notes

* F (2, 85) = 37.88, P < .001

** t(55) = 7.83, P < .001

*** t(55) = 8.69, P < .001

¹ Using the standard formula by Schmidt (1988, p. 269, Log2 (2A/W)), with the width (W) of 3 cm and the amplitude (A) of 20 cm, the Log₂ was 2 × 20/3 = 13.33. To find the Log2 (13.33), using the table (Logarithms to the base 2, Schmidt, 1988, p. 515), enter the row labeled 13, then move to right under the column headed .3; the Log2 (13.33) is 3.73.

² Movement speed and accuracy have a “trade-off” relationship (Fitts, 1954). Because the quality and characteristics of the unsuccessful (missing the target) and successful trials differ in execution speed, movement trajectory, and end-point accuracy, to standardize the arm movement performed and emphasize the effects of movement speed and accuracy on movement execution, only the successful trials were analyzed. Typically, seniors with motor problems would compensate movement accuracy by reducing movement speed (Yan, 2000).

³ The common measure of absolute jerk (length²/duration⁵) involves integrating the square of the absolute jerk over time. Thus, absolute jerk is influenced by movement speed or duration (Schneider & Zernicke, 1989) and may not be suitable for senior participants (AD, MCI, and controls) who have a greater variability in arm movement velocities. To remove the influence of movement duration or velocity, the procedure of normalizing movement jerk was used (Teulings et al., 1997).