The Department of Neurophysiology/EEG at Holy Name Medical Center offers a wide array of Electroneurodiagnostic tests, which study and record the electrical activity in the brain and nervous system. These types of tests are performed by technologists who record information on paper or computer, and the results are interpreted by a specially trained physician.
An EEG records the electrical activity of the brain. Highly sensitive monitoring equipment records the activity through electrodes that are placed at measured intervals on a patient's scalp.
EEGs assist physicians in the diagnosis of a variety of neurological problems, from common headaches and dizziness to seizure disorders, strokes, and degenerative brain disease. The EEG is also used to look for organic causes of psychiatric symptoms and disabilities in children, and can assist physicians in determining irreversible brain death.
For the patient, the test is not painful. The head is measured and the electrodes are placed on the scalp with a paste-like substance. The test itself usually takes about 90 minutes, and the principal role of the patient is simply to remain still, relaxed and comfortable. During the test, the patient may be asked to take repeated deep breaths and may be shown a strobe light that flashes at different speeds. Both activities can help reveal different brain patterns that are useful for diagnosis. Sometimes, physicians also want to observe brain patterns that occur during sleep. For sleep tests, the patient may be asked to stay awake most of the night prior to the EEG appointment or in some cases may be given a mild sedative.
Evoked Potential (EP)
The EP is a recording of electrical activity from the brain, spinal nerves or sensory receptors in response to specific external stimulation. Electrodes are applied to the scalp and other areas of the body, a series of stimuli is introduced, and a computer records the neurological responses. Hundreds of response are received, amplified and averaged by a computer. The final response is plotted on a graph and intercepted by a physician who looks for particular waveforms and the time it takes for them to occur.
Evoked potentials are helpful in evaluating a number of different neurological problems, including spinal cord injuries, acoustic neuroma and optic neuritis, and each type of EP looks at a different neurological pathway. The three most common types are the brainstem auditory evoked potential (BAEP), the visual evoked potential (VEP) and the somatosensory evoked potential (SSEP).
- Auditory: The BAEP assists in evaluating the auditory nerve pathways from the ears through the brainstem. Electrodes are attached to the scalp and earlobes, and earphones are placed over the ears. The phones deliver a series of clicks or tones to each ear separately.
- Visual: VEP's evaluate the visual nervous system from the eyes to the occipital (visual) cortex of the brain. Electrodes are applied to the scalp, and the patient is usually asked to stare at a pattern on a video screen while remaining fully alert. Each eye is tested separately.
- Somatosensory: SSEP's assess pathways from nerves in the arms or legs, through the spinal cord, to the brainstem or cerebral cortex. Electrodes are placed on the scalp and along the spinal cord, and a small electrical current is then applied to the skin overlying nerves on the arms or legs. The current creates a tingling sensation but is not painful. Each leg or arm is tested separately.
24-Hour Ambulatory EEG
The Ambulatory EEG records brain activity for 24 hours on a small tape recorder that is worn around the waist. Electrodes are applied to the scalp with a glue-like substance, and the patient is sent home with a diary to record activities and any symptoms during the 24 hours.
Long-term Epilepsy Monitoring
Long-term monitoring is the simultaneous recording of EEG and videotaped behavior over extended periods of time. It is useful in diagnosing patients with intermittent or infrequent disturbances. These lengthy tests are performed in the lab, using special computers.