EEG or Electroencephalography
Electroencephalography is a test
that measures brain electrical activity.
Electroencephalogram; Brain wave
(EEG) is a test to detect abnormalities in the electrical
activity of the brain.
How the test is performed
Brain cells communicate by
producing tiny electrical impulses. In an EEG, electrodes
are placed on the scalp over multiple areas of the brain to
detect and record patterns of electrical activity and check
The test is performed by
an EEG technician in a specially designed room that may be
in your health care provider's office or at a hospital. You
will be asked to lie on your back on a table or in a
The technician will apply
between 16 and 25 flat metal discs (electrodes) in different
positions on your scalp. The discs are held in place with a
sticky paste. The electrodes are connected by wires to an
amplifier and a recording machine.
The recording machine
converts the electrical signals into a series of wavy lines
that are drawn onto a moving piece of graph paper. You will
need to lie still with your eyes closed because any movement
can alter the results.
You may be asked to do
certain things during the recording, such as breathe deeply
and rapidly for several minutes or look at a bright
How to prepare for the
You will need to wash your
hair the night before the test. Do not use any oils, sprays,
or conditioner on your hair before this test.
Your health care provider
may want you to discontinue some medications before the
test. Do not change or stop medications without first
consulting your health care provider.
You should avoid all foods
containing caffeine for 8 hours before the test.
Sometimes it is necessary
to sleep during the test, so you may be asked to reduce your
sleep time the night before.
How the test will feel
This test causes no
discomfort. Although having electrodes pasted onto your skin
may feel strange, they only record activity and do not
produce any sensation.
Why the test is performed
EEG is used to help
diagnose the presence and type of seizure disorders, to look
for causes of confusion, and to evaluate head injuries,
tumors, infections, degenerative diseases, and metabolic
disturbances that affect the brain.
It is also used to
evaluate sleep disorders and to investigate periods of
unconsciousness. The EEG may be done to confirm brain death
in a comatose patient.
EEG cannot be used to
"read the mind", measure intelligence, or diagnose mental
Brain waves have normal
frequency and amplitude, and other characteristics are
What abnormal results mean
Abnormal findings may
indicate the following:
Seizure disorders (such as epilepsy or convulsions)
Structural brain abnormality (such as a brain tumor or
Head injury, encephalitis (inflammation of the brain)
Hemorrhage (abnormal bleeding caused by a ruptured
Cerebral infarct (tissue that is dead because of a
blockage of the blood supply)
Sleep disorders (such as narcolepsy)
EEG may confirm brain
death in someone who is in a coma.
under which the test may be performed:
Arteriovenous malformation (cerebral)
Benign positional vertigo
Complicated alcohol abstinence (delirium tremens)
Dementia due to metabolic causes
Febrile seizure (children)
Generalized tonic-clonic seizure
Metastatic brain tumor
Partial (focal) seizure
Partial complex seizure
Petit mal seizure
Senile dementia (Alzheimer's type)
Syphilitic aseptic meningitis
Temporal lobe seizure
What the risks are
The procedure is very
safe. If you have a seizure disorder, a seizure may be
triggered by flashing lights or by hyperventilation. The
health care provider performing the EEG is trained to take
care of you if this happens.