Clinical Neurophysiology: Training and Normative Values

This training protocol has two objectives: 1) to train NINDS fellows in specialized techniques for diagnosing neurological disorders, and 2) to gather data from healthy volunteers and from patients with various disorders needed for tests to diagnose disorders of nerve, muscle, and the areas of the brain controlling movement.

Healthy volunteers and patients with neurological disorders of nerve and muscle who require specialized diagnostic testing may be eligible for this study. Candidates must be 18 years of age or older. They are screened with a medical history and neurological examination.

Immediately after screening, participants undergo one or two of the following tests:

• Transcranial magnetic stimulation: This procedure maps brain function. A wire coil is held on the scalp, and a brief electrical current is passed through the coil, creating a magnetic pulse that stimulates the brain. During the stimulation, the subject may be asked to tense certain muscles slightly or perform other simple actions. The stimulation may cause a twitch in muscles of the face, arm, or leg, and the subject may hear a click and feel a pulling sensation on the skin under the coil. During the stimulation, electrical activity of muscles is recorded with a computer, using electrodes (small metal disks) attached to the skin with tape.
• Electromyography (EMG): This test measures the electrical activity of muscles and is used to diagnose problems with the nerves or muscles. For surface EMG, electrodes are filed with a conductive gel and taped to the skin. Needle EMG involves inserting a needle into a muscle to record the electrical activity. Single fiber EMG uses specialized needles that allow recording from single muscle fibers. The needle is inserted into a muscle and the subject is asked to tense that muscle slightly.
• Nerve conduction study: This test measures the speed with which nerves conduct electrical impulses and the strength of the connection between the nerve and the muscle. It is done by taping wires on the skin to record the impulses and placing a probe on the skin to deliver a small electrical stimulus.
• Near-nerve recording: This test is a nerve conduction study that is used to measure responses from very small nerves. It uses a needle placed under the skin to record the nerve response.
• Quantitative sensory testing: This test measures how well the subject feels vibration and cold. A probe that can vibrate or cool down is attached to the subject's finger or foot. The subject presses a button when he or she feels the stimulus. A computer adjusts the intensity of the stimulus to find the lowest level the subject can feel.
• Nerve ultrasound: This test uses sound waves to examine the nerves. Warm gel is applied to the skin and a probe is held on the skin surface.