Electroencephalography (EEG) is the
recording of electrical potentials generated by nerve cells n the cerebral
cortex.
Routine electroencephalography is the
recording of these electrical activities on the scalp. However it
provides a highly limited view of cerebral activity due to inherently poor
spatial resolution and low amplitude as well insensitivity to electrical
fields that are either not perpendicular to the scalp or distant from
it.
Recording the low amplitude cerebral
activity, especially in the context of the larger amplitudes of muscle
potentials, EKG and ambient noise requires powerful amplifiers
and special techniques of canceling the extracerbral electrical
noise.
Recording electrodes consist of small
metal cups or discs which are attached to the scalp so that they make good
mechanical and electrical contact.They cover the surface of the head at
regular intervals. The location of electrodes on the scalp are
standardized by international 10-20 system of electrode placement.This
system uses standard measurements of the head with reference to visible
landmarks. This minimizes the variation in electrode placement among the
laboratories and technologists and provides a uniform reference to
corresponding brain structures among patients.
The EEG machine receives electrical
inputs from the scalp electrodes and after several levels of
amplifications as well as passing through different filters it projects it
on writing devices or the computer monitor.
The main purpose of doing EEG on a
patient is recording certain abnormalities which are well defined as
certain disease features. These abnormal electrical discharges will show
epileptic activities, certain metabolic or toxic conditions affecting the
brain. Particular abnormal patterns are present in certain infections of
the brain.
EEG is one of the diagnostic tool
utilized by the neurologists to assist in the diagnosis of number of
illnesses( such as epilepsy) which may adversely affect the brain.
The findings must be interpreted in the context of the whole clinical
presentation.
