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NEUROPHYSIOLOGY TESTS - EEG, NCV-EMG, VEP, BAER

EEG -

An electroencephalogram (EEG) is a test that measures and records the electrical activity of the brain. Special sensors (electrodes ) are attached to child’s head and hooked by wires to a computer. The computer records brain's electrical activity on the screen as wavy lines. Certain conditions, such as seizures, can be seen by the changes in the normal pattern of the brain's electrical activity.
An electroencephalogram (EEG) may be done to:

• Diagnose epilepsy and see what type of seizures are occurring. EEG is the most useful and important test in confirming a diagnosis
  of epilepsy.

• Find out if a person who is in a coma is brain-dead.

• Study sleep disorders, such as narcolepsy.

• Help find out if a person has a physical problem (problems in the brain, spinal cord, or nervous system) or a mental health problem.

Procedure

• Shampoo the hair and rinse with clear water the evening before or the morning of the test. Do not put any hair conditioner or oil on
   after shampooing.

• To find certain types of abnormal electrical activity in the brain, child may have to be asleep during the recording. Make the child sleep less
   (about 4 or 5 hours) by going to bed later and getting up earlier than usual. Try to keep the child from taking naps just before the test.

• During the monitoring photic stimulation (flashing lights) may be used and hyperventilation may be requested.


Risks

An electroencephalogram (EEG) is a very safe test. THERE IS NO RISK. The electrical activity of brain is recorded, but at no time is any electrical current put into body. An EEG should not be confused with electroshock (electroconvulsive) therapy.

Results

There are several types of brain waves:

• Alpha waves have a frequency of 8 to 12 cycles per second. Alpha waves are present only in the waking state when your eyes are closed
   but you are mentally alert. Alpha waves go away when your eyes are open or you are concentrating.

• Beta waves have a frequency of 13 to 30 cycles per second. These waves are normally found when you are alert or have taken high doses
   of certain medicines, such as benzodiazepines.

• Delta waves have a frequency of less than 3 cycles per second. These waves are normally found only when you are asleep or in
    young children.

• Theta waves have a frequency of 4 to 7 cycles per second. These waves are normally found only when you are asleep or in young children.




Electroencephalogram (EEG)



Normal: In adults who are awake, the EEG shows mostly alpha waves and beta waves.
The two sides of the brain show similar patterns of electrical activity.
There are no abnormal bursts of electrical activity and no slow brain waves on the EEG tracing.
If flashing lights (photic stimulation) are used during the test, one area of the brain (the occipital region) may have a brief response after each flash of light, but the brain waves are normal.
Abnormal: The two sides of the brain show different patterns of electrical activity. This may mean a problem in one area or side of the brain is present.
The EEG shows sudden bursts of electrical activity (spikes) or sudden slowing of brain waves in the brain. These changes may be caused by a brain tumor, infection, injury, stroke, or epilepsy. When a person has epilepsy, the location and exact pattern of the abnormal brain waves may help show what type of epilepsy or seizures the person has. Keep in mind that in many people with epilepsy, the EEG may appear completely normal between seizures. An EEG by itself may not diagnose or rule out epilepsy or a seizure problem.
The EEG records changes in the brain waves that may not be in just one area of the brain. A problem affecting the entire brain-such as drug intoxication, infections (encephalitis), or metabolic disorders (such as diabetic ketoacidosis) that change the chemical balance in the body, including the brain-may cause these kinds of changes.
The EEG shows delta waves or too many theta waves in adults who are awake. These results may mean brain injury or a brain illness is present. Some medicines can also cause this.
The EEG shows no electrical activity in the brain (a "flat" or "straight-line" EEG). This means that brain function has stopped, which is usually caused by lack of oxygen or blood flow inside the brain. This may happen when a person has been in a coma. In some cases, severe drug-induced sedation can cause a flat EEG


What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

 

• Moving too much.

• Taking some medicines, such as those used to treat seizures (antiepileptic medicines) or sedatives, tranquilizers, and barbiturates.

• Drinking coffee, soda, tea, or other foods that contain caffeine before the test.

• Being unconscious from severe drug poisoning or a very low body temperature (hypothermia).

• Having hair that is dirty, oily, or covered with hair spray or other hair preparations. This can cause a problem with the placement of
   the electrodes.

What To Think About

• If the doctor thinks that a person has epilepsy but the EEG is normal, the technologist running the EEG test may have the person look at a flashing light (photic stimulation), breathe fast and deeply (hyperventilation), or sleep during the test. These techniques sometimes show epileptic EEG patterns that did not show up at first. If epilepsy is suspected after an initial EEG, the doctor may repeat the EEG more than once.

• An EEG done during a seizure will almost always show abnormal electrical patterns. This makes an EEG useful when a doctor thinks that a person is having psychogenic seizures (pseudoseizures), which have no physical cause but can be caused by stress, emotional trauma, or mental illness. Psychogenic seizures do not cause abnormal electrical activity in the brain and will not show abnormal EEG results.