Electroencephalography

Electroencephalography is the neurophysiologic exploration of the electrical activity of the brain by the application of electrodes to the scalp. The resulting traces are known as an electroencephalogram (EEG) and represent so-called brain waves. This device is used to assess brain damage, epilepsy and other problems. EEG can also be used in conjunction with other types of brain imaging

The recording is obtained by placing electrodes on the scalp, usually after preparing the scalp area by light abrasion and application of a conductive gel to reduce impedance. Neuroscientists and biological psychiatrists use EEGs to study the function of the brain by recording brain waves during controlled behavior of human volunteers and animals in lab experiments. Theories to explain sleep often rely on EEG patterns recorded during sleep sessions. In addition, the procedure is used clinically to assist in the diagnosis of epilepsy.

Wave types

Historically four major types of brainwave are recognized (alpha, beta, delta and theta).

• Beta is the frequency range above 12 Hz (there's no precise agreement on the frequency ranges for all the frequency bands mentioned here). It's often associated with active, busy or anxious thinking and active concentration.
• Alpha (aka Berger's wave) is the frequency range from 8.5 Hz to 12 Hz. It's often associated with an alert adult and is present by the age of two years. Alpha rhythms are best seen with the eyes closed. It attenuates with drowsiness and eyes open.
• Theta is the frequency range from 4.5 Hz to 8 Hz and is associated with drowsiness, childhood, adolescence and young adulthood. Theta can also be produced by hyperventilation in people without it being an abnormal phenomena.
• Delta is the frequency range up to 4 Hz and is often associated with the very young and certain encephalopathies and underlying lesions. It is seen in sleep, but generally is associated with other frequencies to become waveforms such as Vertex Sharp Waves.

History

Richard Caton (1842–1926), a physician practicing in Liverpool, presented his findings about electrical phenomena of the exposed cerebral hemispheres of rabbits and monkeys in 1875.

German physiologist Hans Berger (1873–1941) began his studies of the human EEG in 1920. He gave the device its name and is sometimes credited with inventing the EEG, though others had performed similar experiments. His work was later expanded by Edgar Douglas Adrian.

In the 1950s, English physician Walter Grey Walter perfected an improvement to EEG called EEG tomography which allowed for the mapping of electrical activity across the surface of the brain.

See also

electroencephalophone.