What is Electro
In the late
1920s a German psychiatrist named Hans Berger was measuring the brain waves
of his daughter when she was doing mental arithmetic. He found that
the activity increased when she was trying to multiply difficult numbers.
From this evidence, he deduced that the frequency of the wave pattern from
the recording reflected the amount of wave activity in his daughter's brain.
Since then, EEG has
been perfected as a cheap and accurate way of measuring brainwave activity
in the outer layer of the brain. Sensitive electrodes are attached
to the head, and the signals are amplified to give a graph of electrical
potential versus time. It can be measured and compared at different
spots on the head simultaneously, to give a 2-dimentional activity map
of the cerebral cortex. EEG is often used
to diagnose sezure disorders, tumors, head injuries, degenerative diseases
and brain death. It is also used in research on brain activity.
Sometimes, the brain
waves are recorded for a special stimulus, and the experiment is repeated
several times. The graphs are then averaged, and the resulting data
are called event-related
potentials. These were important in
the 60s and 70s when researchers were trying to find out if certain regions
of the cerebral cortex were specialized to perform some tasks. ERPs
have also been useful for finding out how long the brain uses to process
different kinds of information, and monitor levels of attention and stress
for various experiments.
The major advantage
of EEG over visual methods is a very low price. In addition, the
equipment is portable; all you need is some electrodes, a reliable signal
amplifier and a computer which records or shows the data. The signals
can even be transmitted via a radio link before they are recorded.
This way, it is possible to record the brain activity of people while they
are performing a task or activity. It is also the only way of measuring
brain activity in real time, since the time aspect of the graph is measured
The major drawback
of EEG is that it cannot measure activity or structure beyond the cerebral
cortex. Hence, EEG is often used in combination with MRI.
This will allow brain activity to be determined in relation to subcortical
(beneath the cortex) structures.
If you are going
to have your brain activity monitored with EEG, there are very few preparations
to make. The method is completely noninvasive, and there are no dieting
rules. Depending on the extent of the experiment, you may have to
shave little spots of your head for the electrodes to work. Also
be sure to be well rested and relaxed, as stress or lack of sleep will
change your brain wave patterns.
There is a similar
method to EEG called magnetoencephalography,
which measures the magnetic fields created by the electrical activity of
the brain, rather than the activity itself. Some scientists claim
that these signals are less distorted by the skull and skin tissue, but
no experimental data exists to support this. Hence, the accuracies
of EEG and MEG seem to be comparable.