EEG is the recording of electrical activity along the scalp produced by the firing of neurons within the brain. In clinical contexts, EEG is the recording of the brain’s spontaneous electrical activity over a short period of time, usually 20-40 minutes, by placing multiple electrodes on the scalp.
EEG is mainly used in the diagnosis of epilepsy, as epileptic activity can create clear abnormalities on a standard EEG study. Another clinical use of EEG is in the diagnosis of coma and Encephalopathies. EEG is also used as a first-line method for the diagnosis of tumors, stroke and other focal brain disorders.
The activity measured by EEG is the electrical potentials created by the post-synaptic currents. More specifically, the scalp electrical potentials that produce EEG are due to the extracellular ionic currents caused by Dendritic electrical activity.
Brain Wave Patterns
The Electroencephalography mainly relies on the wave patterns appearing in the recorder. The human brain generates different forms of brain wave depending on the mental state. These brain waves are classified into the following types
Hans Berger named the first rhythmic EEG activity he saw, the “alpha wave.”Alpha is the frequency range from 8 Hz to 12 Hz. This is activity in the 8-12 Hz range seen in the posterior regions of the head on both sides, being higher in amplitude on the dominant side. Alpha wave is found when closing the eyes and in the relaxed state.
Beta is the frequency range from 12 Hz to about 30 Hz. It is seen usually on both sides in symmetrical distribution and is most evident frontally.
Beta wave appears when the body is
Beta waves also appear as a result of drugs such as Benzodiazepines.
Gamma is the frequency range approximately 26–100 Hz. Gamma rhythms are thought to represent binding of different populations of neurons together into a network for the purpose of carrying out a certain cognitive or motor function.
Delta is the frequency range up to 3 Hz. It tends to be the highest in amplitude and the slowest waves.
It is seen normally
1. In adults during slow wave sleep.
2. In babies
Theta is the frequency range from 4 Hz to 7 Hz. Theta is seen normally seen
1. In young children. It may be seen
2. In drowsiness or arousal in older children and adults
3. In meditation
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