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). There is no precise agreement on the frequency ranges for each type.
- Alpha (Berger's wave) is the frequency range from 8.5 Hz to 12 Hz. It is often associated with an alert adult and is present by the age of two years. Alpha rhythms are best detected with the eyes closed. It attenuates with drowsiness and open eyes.
- Beta is the frequency range above 12 Hz and is often associated with active, busy or anxious thinking and active concentration.
- 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.
- Theta is the frequency range from 4.5 Hz to 8 Hz and is associated with drowsiness, childhood, adolescence and young adulthood. This EEG frequency can sometimes be produced by hyperventilation. Theta waves can be seen during trances, hypnosis, deep day dreams, lucid dreaming and light sleep and the preconscious state just upon waking, and just before falling asleep. Controlled meditation or yogic meditation and/or breathing also produces theta waves. Mystics and Yogis are said to remain conscious and in control at this and at the Delta state.
Entraining the brain to a desired state
Computer programs such as Noromaa Solutions Oy's Brainwave Generator are able to stimulate the brain and alter the brain's frequency via an audio stimulus.
For example, if a person is in beta stage (highly alert) and a stimulus of 10Hz is applied to his/her brain for some time, the brain frequency is likely to change towards the applied stimulus. The effect will be relaxing to the person. This phenomenon is also called frequency following response. Entrainment works more efficiently if the stimulus applied to the brain begins at the brain's current frequency, then sweeps to the desired frequency. In practice, it is difficult to determine your brain state without extra equipment (like EEG devices).
To simulate the brain effectivly with audio, binaurial beat frequencies must be used, since the ears cannot hear sounds low enough to be useful for brain stimulation. If the left ear is presented with a steady tone of 500Hz and the right ear a steady tone of 510Hz, these two tones combine in the brain. The difference, 10Hz, is perceived by the brain and is a very effective stimulus for brainwave entrainment. This 10Hz is formed entirely by the brain. When using stereo headphones, the left and right sounds do not mix together until in your brain. The frequency difference, when perceived by brain this way, is called a binaural beat.
Altering the brain's electral activity can be useful for lucid dreaming, encouraging alertness, astral projection, or simply in order to relax.
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
External links
- OpenEEG - An open source hardware and software project to enable hobbyists to build their own EEG machine (mostly for biofeedback purposes).
- Brainwave Generator - A shareware software program which produces binaurial beat frequencies inorder to entrain the brain into a specific state