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Electroneurodiagnostic technology is the scientific field devoted to the recording and study of electrical activity of the brain and nervous system.  Used for medical evaluation and research, it includes procedures that access the function of the nervous system. 

Technologists record electrical activity arising from the brain, spinal cord, peripheral nerves, or somatosensory systems using a variety of techniques and equipment.  Technologists also prepare the patients for procedures, record electrical potentials, obtain medical histories, calculate results, and maintain equipment.  They work with specially-trained physicians who interpret the data and provide clinical impressions.

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 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 (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 prior to the EEG appointment or, in some cases, may be given a mild sedative.  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. 

Intraoperative Monitoring
Sometimes, patients having surgery on arteries in the neck or around the heart will have EEG monitoring throughout the time they are in the operating room.  This provides the surgeon with additional information about brain function during the surgery.

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.

Evoked Potentials (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 responses are received, amplified and averaged by a computer.  The final response is plotted on a graph and interpreted by a physician who looks for particular waveforms and the time it takes them to occur. 

Evoked potentials are 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 listed below:

• Auditory: The BAEP assists in evaluating the auditory nerve pathways from the ears through the brainstem.  Earphones deliver a series of clicks or tones to each ear separately.
  
  
• Visual: VEPs evaluate 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: SSEPs assess 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. 
  
  
• Intraoperative Monitoring: Evoked potentials are sometimes used to assess nerve function during surgical procedures involving the spinal cord or brain.  The technologist is responsible for monitoring this information and providing a technical description to the surgeon to allow him/her to make changes to avert any permanent damage to the patient?s function.

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 next 24 hours.

Polysomnograms (PSG)
A PSG is a recording during sleep that uses EEG and other physiologic measures to evaluate sleep disorders.  Patients usually spend one or two nights in the lab being monitored.  A technologist records various information for interpretation by a special physician. 

The test is used to help evaluate patients who experience excessive sleepiness during the day or who have trouble falling asleep or staying asleep at night.  Three common sleep disorders are sleep apnea, insomnia, and narcolepsy.

Nerve Conduction Studies (NCS)
Nerve Conduction Studies are performed by placing surface electrodes over a particular nerve, or a muscle innervated by that nerve, and using electrical stimulation to activate the nerve.  When the nerve is stimulated, the patient feels a tingling sensation. 

The data collected is evaluated by a physician specializing in electrodiagnostic medicine.  Patients referred for NCS tests suffer from nerve conditions which produce numbness, tingling, pain or loss of sensation, or neurological diseases affecting primarily the peripheral nervous system.