Electroneurodiagnostics
Great River Medical Center

Electroneurodiagnostics is the study and recording of electrical activity in the brain and nervous system. Technologists perform the tests, and a neurologist interprets the test results and then reports these findings to the referring physician. This following explains some of the most-common tests.

Electroencephalogram (EEG)

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.

The test is not painful. The head is measured and the electrodes are placed on the scalp with a pastelike 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 (hyperventilate) 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 before the EEG appointment or, in some cases, may be given a mild sedative.

EEG helps physicians diagnose a variety of neurological problems, from common headaches and dizziness to seizure disorders, stroke and degenerative brain disease. EEG also is used to look for organic causes of psychiatric symptoms and disabilities in children, and can help physicians determine irreversible brain death.

Evoked Potential (EP)

An 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. The patient then receives a series of painless stimuli, and a computer records the neurological responses. Hundreds of responses are received, amplified and averaged by a computer. The final response is plotted on a graph and interpreted by a neurologist who looks for particular waveforms and the time it takes for them to occur.

EP is helpful in evaluating a number of different neurological problems, including spinal-cord injuries, acoustic neuroma and optic neuritis. Each type of EP looks at a different neurological pathway. The most common types are:

•	Auditory – The brainstem auditory evoked potential helps evaluate the auditory nerve pathways from the ears through the brainstem. Earphones deliver a series of clicks or tones to each ear separately.
•	Visual – The visual EP evaluates the visual nervous system from the eyes to the occipital (visual) cortex of the brain. The patient is usually asked to stare at a pattern on a video screen while remaining fully alert. Each eye is tested separately.
•	Somatosensory – This EP assesses pathways from nerves in the arms or legs, through the spinal cord, to the brainstem or cerebral cortex. A small electrical current is 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 gluelike substance, and the patient is sent home with a diary to record activities and any symptoms during the 24 hours.

For more information

For more information, please call Great River Medical Center’s Electroneurodiagnostics Laboratory at (319) 768-4325.