This study will determine whether stimulating the nerves or the brain can modify the spinal
reflex that controls the muscles that flex and extend the ankle. Training spinal nerve
networks with sensory input may provide a way of re-establishing movements, such as walking,
in patients with spinal injury.
Healthy normal volunteers with no history of peripheral neuropathy or radiculopathy, ankle
contractures or tendon surgery may be eligible for this study. Participants will undergo
three stimulation procedures, each in a different session, to measure leg muscle reflexes.
The procedures are:
- Reflex testing - Metal electrodes are taped to the skin over the leg muscles. A small
electrical pulse is delivered through the electrodes to stimulate two nerves to the
muscles. This evokes a reflex between the ankle flexor and extensor muscles. The
responses to several dozen stimuli are averaged.
- Nerve stimulation - The nerve to the muscle that flexes the leg is electrically
stimulated near the knee through electrodes taped to the skin. The strength of the
stimulus is adjusted to produce little or no muscle movement. The stimulation is
repeated every few seconds for 45 minutes.
- Transcranial magnetic stimulation - An insulated wire coil is placed on the subject's
scalp. A brief electrical current passes through the coil, creating a magnetic pulse
that travels through the scalp and skull and causes small electrical currents in the
outer part of the brain. There may be twitching in the muscles of the arm or leg.
During the stimulation, the subject may be asked to tense certain muscles slightly or
perform other simple actions to help determine the best position for the coil over the
part of the brain that controls the leg. The leg is then stimulated once every 10
seconds, combined with nerve stimulation every 1 to 2 seconds.
Training of spinal interneuronal networks may offer a means for re-establishing movements
such as locomotion in patients with spinal injury. Sensory feedback in the pattern which
results from the leg movement is hypothesized to be the critical component for training
spinal networks. This protocol will address the basic assumption underlying such training:
can a specific pattern of sensory input modify the strength of a spinal cord circuit? We
will test whether peripheral nerve stimulation can modify the strength of the spinal reflex
mediating reciprocal inhibition between ankle flexor and extensor muscles in normal
subjects, comparing patterned and unpatterned stimulation.
Healthy adult volunteers willing to participate
History of peripheral neuropathy or radiculopathy
Implanted devices, including pacemakers, pumps, and defibrillators
Ankle contractures or tendon surgery