Motor Skill Learning: Spinal Reflexes

Objective: Once a skilled movement is thoroughly learned, it can be performed relatively automatically. The motor cortex is active when learning a new motor skill, but becomes less activated once the skill has become over-learned. We hypothesize that learning a skilled movement is associated with more efficient use of subcortical motor circuits. Subcortical motor circuits can coordinate features of the intended movement such as the timing and patterns of activation of different muscles. The goal of this study is to determine whether learning a motor skill strengthens spinal interneuron circuits that facilitate the movement. Subjects will learn to perform a movement consisting of alternating wrist movements. The strength of reciprocal inhibition between antagonist muscles will be tested. Study Population: 22 healthy adult volunteers Design: The study has two experiments. Both experiments use a within-subjects design. The purpose of the first experiment is to determine whether learning to accurately perform an alternating wrist flexion and extension movement task is associated with reduced co-contraction of wrist flexor and extensor muscles. Subjects will practice making accurate wrist flexions and extensions to keep a cursor on a target for fifteen-minute sessions every weekday until they are able to obtain 95% accuracy. Activity of the arm muscles will be monitored during the sessions with surface electrodes on the arm muscles. The first experiment will also determine the best training parameters for learning the task. In the second experiment, a second group of subjects will learn the task using the best training parameters. The strength of the reflex for reciprocal inhibition will be measured before, during and after training. Reciprocal inhibition will also be measured after the movement has become highly learned. Outcome measures: In the first experiment, the outcome will be the percent of movement time in which co-contraction occurs, as recorded from surface electrodes, while the subject learns to perform the movement to 95% accuracy. In the second experiment, the outcome measure is the strength of spinally mediated reciprocal inhibition, as measured using reflexes.