The brain is an electrochemical organ. The electrical activity of the brain is displayed in the form of brainwaves. These waves, called electroencephalography, or EEG, were first discovered by Richard Caton in 1875. At first, investigators focused on how changes in the ongoing EEG related to stages of sleep. Then, it was discovered that EEG rhythm changed with age, was vulnerable to sensory stimulation, and was affected by body chemistry. Later, scientists learned that EEG can be used to diagnose many illnesses such as epilepsy. During more modern times, the focus in EEG research has been on applying knowledge about the neural bases of human perception, cognition and emotions.
Brainvaves and Stages of Arousal
Brainwaves range from the most active to the least active, or from high amplitude waves with low frequency to low amplitude waves with high frequency. When the brain is actively engaged in some activity, beta waves can be recorded. These are fast and relatively low in amplitude. Alpha waves represent non-arousal and are slower and higher in amplitude. Theta brainwaves are even slower and bigger in amplitude. A person who cannot recall how he drove home from work is usually in a theta brainwave state, characteristic to daydreamers. Delta brainwaves are of great amplitude and slow frequency and are present in a sleeping individual.
Clinical Use of Brainwaves
The most common clinical use of EEG is to test and diagnose epilepsy. It should be noted, however, that EEG is valuable tool in diagnosing and following other neurological conditions, such as brain maturation in children, clinical brain death, encephalopathy and focal central nervous system.
Event-Related Potentials
Ongoing EEG is affected by many things besides the electrical activity of the brains. These so-called artifacts include such things as eye movement and muscle activity. Usually these actions cause electrical activity that is much larger in size than those caused by the electrical activity of the brains. Thus, when how the brains react to a stimulus, such as a sound, is being studied, all activity other than that of the brain needs to be eliminated. This is typically done by averaging, a process of repeating the stimulus over a period of time and then averaging the EEG recorded slightly before the stimulus to few hundred milliseconds after it. By using this process, it is possible to take out electrical activity that is not related to that particular stimulus. By using such technique, it is possible to employ brainwaves to study higher-order cognitive functions such as memory, learning or responses to sensory stimuli such as sounds or visual images.
