Electroencephalograms (EEGs): Catching a Brain Wave

In this era of rapidly developing technology for medical imaging, one test that might seem downright old-
fashioned is an electroencephalogram (EEG) or brain-wave test. But by its very nature, the EEG test will
continue to occupy a valuable niche in medical diagnosis that brain-imaging tests—like CT scans and MRI
scans—will never fill.

Rather than making pictures of the brain's anatomy, EEGs evaluate the brain's physiology. So while
imaging tests won't replace electroencephalograms, EEGs won't replace imaging tests, either. The testing
methods look at the brain from completely different points of view, each valuable in its own way.

Broken into its parts, the term electroencephalogram means "electrical brain recording."

Hans Berger, a German scientist, got the ball rolling in 1924 with the first recordings of human brain-
waves. Since then, the basic principles of recording EEGs have remained the same, but the electronics
have gotten better—and smaller. In an EEG recording, tiny voltage-fluctuations from the brain are picked
up by a standard array of metal disks attached to the scalp and are then amplified electronically in order to
create a permanent recording.

If you are old enough, you might remember the 1960s fascination with alpha waves which people tried to
enhance via biofeedback devices. Alpha waves are rhythmic brain-signals oscillating between 8 and 13
times per second that can be measured from the back of the head during quiet wakefulness.

Additional voltage-rhythms encountered during clinical recordings include theta and delta waves that
oscillate more slowly than alpha waves, and beta waves that oscillate more rapidly. All four rhythms can be
seen in normal states of alertness, drowsiness or sleep, and should be the same on both sides of the brain.

The premier use of EEGs is to evaluate people with known or suspected epilepsy (seizure disorders).
Seizures are highly electrical events in the brain that cause temporary alterations in the patient's
consciousness, perceptions or behavior.

In healthy circumstances, the brain's approximately 20 billion brain cells perpetually signal each other via
electrical impulses. Collectively, these impulses traveling among networks of brain-cells are the means by
which the brain performs its functions—like perceiving, pondering, remembering, calculating and deciding.
A poetic scientist described the brain and its normal functioning as "an enchanted loom where millions of
flashing shuttles weave a dissolving pattern, always a meaningful pattern though never an abiding one; a
shifting harmony of subpatterns."

But in epileptic attacks, salvo upon salvo of excessive discharges overwhelm the brain's circuits and
disrupt their normal functions. Suddenly, the enchanted loom's patterns are no longer meaningful or
harmonious.

A seizure-in-progress is readily detected by an EEG recording. However, most patients under evaluation
for seizures don't oblige the doctor by having an attack during a typical 30-90 minute recording session.
Fortunately, for purposes of diagnosis this is not usually necessary. Tell-tale changes in brain-waves are
often present during the periods between attacks—while the patient feels normal—that can reveal a
tendency to epilepsy and even identify specific sub-types.

Two other common uses for EEG testing are for assessment of confusional states and sleeping disorders.

In people with confusion or memory loss, an EEG can show different patterns depending on the cause.
When confusion is caused by a depressed mood, the EEG remains normal. When confusion is caused by
a degenerative dementia like Alzheimer's disease or by a metabolic condition like a drug-overdose, the
brain's rhythms become slower.

For evaluation of sleeping problems, an EEG is just one component of a battery of recording systems.
Through concurrent monitoring of other biological processes—like breathing, blood-oxygenation,
heartbeat, muscle activity and eye movements—conditions such as narcolepsy and obstructive sleep
apnea can be diagnosed.

So what can you expect if your doctor refers you for an EEG study? In many cases, you won't need to
make any special preparations for the test, but in cases where epilepsy is under consideration, you might
be asked to stay awake for much of the preceding night. Sleep-deprivation increases the likelihood of
recording a seizure-related abnormality in patients who have them. You are usually allowed to eat before
the test.

The testing-session lasts about two hours, though can be longer, especially if a sleeping problem is being
evaluated. The EEG technologist uses much of the testing-session to attach about two dozen metal-disk
electrodes to the scalp in standardized locations, and then to test the electrical characteristics of each
electrode to ensure that good connections have been made.

Once the electrodes are in place the recording session can begin. For most of the recording you lie quietly
with your eyes closed. The technologist measures the brain-waves during quiet wakefulness, and then if
you fall asleep, that is recorded, too. In additional parts of the test, you might be asked to breathe rapidly
and deeply for about three minutes (useful in detecting "absence" or "petit mal" epilepsy) or to watch
flashing lights (useful in detecting certain other kinds of epilepsy). Then the electrodes are disconnected
and you go home.

A physician subsequently reads the recording and makes a report. The report includes a description of the
observed rhythms of brain-waves, details of any detected abnormalities and comments about their
possible significance. Your own doctor uses this report along with what else is known about your condition
to make a diagnosis.

If you need an EEG, the good news is that the test is not painful. No needles are involved. There is no
need to shave or otherwise remove hair. The bad news is that the adhesive used to attach the electrodes
to your scalp can take a day or two to scrub out, and might require mineral oil to remove. Beauty-shop
treatments should be postponed until after the EEG appointment; the hair-dresser's efforts will be ruined if
the EEG comes second.

(C) 2005 by Gary Cordingley