Electroencephalography is a method of electric potential differences that have arisen in the brain , via the scalp to register. The electroencephalogram(EEG) can give information about disease processes at both the nature and the place of the drift.

When making an EEG is a number of electrodes placed on the head. Usually these are there about 20 and are confirmed in a kind of hat. A standard system to confirm these electrodes on the scalp is known as the 10-20 system. In order to be able to make good contact with the scalp is between the electrodes and the skin a conductive liquid made contact. The measured voltage is extremely small (approx 100 microvolts) in relation to the additional pollution from the power (1-10 V), the electrocardiogram (ca 1 mV) and elektromyogrammen of muscle contractions elsewhere in the body. A new development is the Ear-EEC, in which the electrical signals from the brain through the skull but not a plug in the ear are measured. This application seems especially suited for ambulatory measurement of brain activity in disorders such as epilepsy or severe fatigue (micro sleep) may occur[1][2]

An EEG signal is displayed as a number of graphs, in which the measured voltage on the vertical axis and time along the horizontal axis. The appearance of this chart can provide information on the State of the brain are located, for example, whether one sleeps, excited or just relax.

EEC is also widely used as a research method in cognitive neuroscience. There is then often made use of so-called Event-related potentials (Erps). This is a test subject repeatedly exposed to a particular type of stimulus (for example, a Show), while an EEG is created. Of the EEG signals is then the average, so that a view of just the brain activity in response to the stimulus remains. One can so the reaction of the brain on compare different types of stimuli.

The devices that made be EEG 's, are subject to the medical devices.

Types of brain waves[Edit]Edit

Type Frequency Description Image
EEC 0-80 Hz Originally one distinguished four types of brain waves (alpha, beta, delta and theta). There is no universal agreement about the exact frequency range of these waves. [1]
Delta 0-4 Hz Delta-waves have a frequency range of 0 to 4 Hz and are common in babies, with certain types of encephalopathy and during deep sleep. [2]
Theta 4-8 Hz Theta waves have a frequency range of 4 to 8 Hz and are common in children, while dozing, dreams and light sleep, just in front of the wake up or fall asleep, and sometimes at hyperventilation. Further it can be resurrected by trance or hypnosis. [3]
Alfa 8-12 Hz Alfa-waves have a frequency range of 8 to 12 Hz. These waves come in people from the second year and indicate that someone is in a relaxed way alert. Alpha waves in drowsiness and when the eyes are open. The waves are common in the occipital cortex (Visual). [4]
SMR 12-16 Hz SMR-waves have a frequency range from 12 to 16 Hz and have to deal with physical rest and sensomotorisch consciousness. [5]
Beta 16-30 Hz Beta-waves have a frequency range of 16 to 30 Hz. Beta-waves with a low amplitude and with multiple different frequencies is often associated with intense active thoughts and concentration. Rhythmic beta-waves with lots of clear frequencies have to do with various pathological of drug-related causes. [6]
Gamma 30-80 Hz Gamma waves have a frequency range of 30 to 80 Hz. Gamma-waves have to do with a strong mental activity such as perception, problem solving, fear and consciousness. [7]

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