Evaluating How the Nervous System Coordinates Voluntary Movement in the Arm

• Afferent nerve-firing patterns [ Time Frame: At the time of the experimental session ] [ Designated as safety issue: No ]
  Nerve firing patterns are described as the sequence of time intervals between action potentials recorded from the nerve.
• Task performance levels [ Time Frame: At the time of the experimental session ] [ Designated as safety issue: No ]
  Task performance most often refers to the accuracy and/or precision of limb movement or of the accuracy and/or precision of detection of a somatosensory stimulus.

• Afferent nerve-firing patterns
• task performance levels

The purpose of this study is to investigate how the nervous system interprets joint position and movement. This will contribute to a broader knowledge of understanding how the human central nervous system (CNS), which includes the brain and spinal cord, coordinates voluntary movement.

In motor nervous system disorders, such as stroke, the CNS is unable to coordinate normal voluntary movement. This is often caused by malfunctioning proprioception. Proprioception is one's sense of the relative position of neighboring body parts. It allows an individual to feel the orientation of one body part to another. It also provides information about the rate and direction of movement so that an individual can change muscle contraction immediately as incoming information about external forces is received. The two main components of proprioception include sensory nerve cells located in the inner ear and stretch receptors located in muscles, skin, tendons, and joint-supporting ligaments. The purpose of this study is to determine how proprioception is communicated from the stretch receptors in skin, joints, and muscles to the CNS. Specifically, the study will compare the differing roles of agonists, muscles that cause movement, versus antagonists, muscles that oppose agonists, in proprioception.

Participants will be assigned to one of seven substudy groups. Each group will partake in one or more study experiments, which will each take 1 to 4 hours. Participants enrolled in more than one experiment will report to the study site on separate days. For each experiment, the participant will sit at a table with a specialized device, called a manipulandum, which has motorized elbow, wrist, and finger manipulators to control the movement and position of a participant's arm. Depending on the experiment, several forms of joint rotation and arm movement will be carried out by either the participant or the manipulandum. Electrical activity of certain muscles and nerves will be recorded in all experiments by various kinds of electrodes. A tendon vibrator will be used in some experiments to activate muscle receptors that signal to what extent and how fast a muscle is contracting or stretching. Regional anesthesia will also be used in some experiments to reduce sensory input from the skin and joints. Participants will receive follow-up phone calls after an experiment to check for any side effects from procedures.

Able bodied adult humans with no ongoing impairments in motor or sensory function.

• Device: Manipulandum table
  A table (device) with rotational actuators for the elbow, wrist and fingers. During experimentation, these joints may be moved, or they may be held in a fixed position while the subject exerts volitional torque on the device, or they may be released for the subject to make free movements.
• Device: Tendon vibrator
  A motor that produces mechanical impulses to be transmitted either directly to the muscle belly or indirectly to the muscle's tendon. These impulses stimulate proprioceptive receptors in the muscle.

Exclusion Criteria for Anesthesia:

• Known neuromuscular abnormalities
• Known allergies or hypersensitivity to anesthetics
• Blood clotting or bleeding disorder
• Use of anticoagulants
• Psychologically inappropriate behavior (e.g., apprehension, uncertainty with procedure)
• Significant history of any cardiovascular problem

Exclusion Criteria for Nerve Recording by Electrode:

• Significant history of fainting or problems with blood pressure control