Motor Skill Learning: Spinal Reflexes

This study will test a spinal cord reflex called reciprocal inhibition before, during, and after learning a motor skill to see if the reflex becomes stronger by learning the movement. People learn new motor skills throughout their lives. At first, performing a new skilled movement such as riding a bicycle takes effort and is clumsy, but with practice, it becomes relatively automatic. The motor cortex (a part of the brain) is very active when a new skilled movement is learned, but becomes less active when the movement is over-learned. This study will determine whether the spinal cord helps coordinate the pattern of activity between groups of muscles once a motor skill is learned.

Healthy volunteers between 21 and 65 years of age may be eligible for this study. Candidates are screened with a medical history and neurological examination.

Participants are divided into two groups. Group 1 has movement training sessions only and Group 2 has both movement training sessions and physiology sessions, as follows:

Movement training sessions

For 15 minutes every weekday, participants practice moving their wrist back and forth to make a cursor on the computer screen follow a target. Activity of the arm muscles is monitored with surface electrodes taped to the skin. The sessions continue until the participant can perform the movement well. Group 1 participants return to the clinic a week after the last session to perform the movement again to see if their skill level has changed. Each session lasts about 20 to 30 minutes.

Physiology sessions

In three separate sessions, the reflex for reciprocal inhibition is measured before and at several times during the movement task. This is done with nerve conduction studies. A probe placed on the skin delivers a low-intensity electrical stimulus. Wires taped to the skin record the nerve impulses. To measure reciprocal inhibition, several dozen stimuli are given to two nerves in combinations. Each session lasts 2 to 3 hours.