Image Denoising by Data Adaptive and Non-Data Adaptive Transform Domain Denoising Method Using EEG Signal - Proceedings of All India Seminar on Biomedical Engineering 2012 (AISOBE-2012) - page 10

Supporting Literature

EEG Signals: The nervous system sends commands and communicates by trains of
electric impulses. When the neurons of the human brain process information they do
so by changing the flow of electrical current across their membranes. These
changing currents (potential) generate electric fields that can be recorded from the
scalp. Studies are interested in these electrical potentials but they can only be
received by direct measurement. This requires a patient to undergo surgery for
electrodes to be placed inside the head. This is not acceptable because of the risk to
the patient. Researchers therefore collect recordings from the scalp receiving the
global descriptions of the brain activity. Because the same potential is recorded from
more than one electrode, signals from the electrodes are supposed to be highly
correlated. These are collected by the use of an electroencephalograph and are called
EEG signals. Understanding the brain is a huge part of Neuroscience, and the
development of EEG was for the explanation of such a phenomenon. The mor-
phology of EEG signals has been used by researches and in clinical practice to:

• Diagnose epilepsy and see what type of seizures is occurring.
• Produce the most useful and important test in conforming a diagnosis of
epilepsy.
• Check for problem with loss of consciousness or dementia.
• Help find out a person's chance of recovery after change in consciousness.
• Find out whether a person is in coma or is brain dead.
• Study sleep disorder such as narcolepsy.
• What brain activity occurs while a person is receiving general anesthesia during
brain surgery.
• Help find out whether a person has a physical problem (in the brain, spinal cord,
or nervous system) or a mental health problem.
The signals must therefore present a true and clear picture of brain activities.
Being a physical system, recording electrical potentials present EEG with prob-
lems; all neurons, including those outside the brain, communicate using electrical
impulses. These non-cerebral impulses are produced from:

• Eye movement and blinking—Electrooculogram (EOG)
• Cardiac movement—Cardiograph (ECG/EKG)
• Muscle movement—Electromyogram (EMG)
• Chewing and sucking movement—Glassokinetic
• The power lines.

EEG recordings are therefore a combination of these signals called artifacts or
noise and the pure EEG signal defined mathematically as in Eq. ( 1 ):

E ð t Þ¼ S ð t Þþ N ð t Þ

ð 1 Þ

where,
S

is pure EEG signal,