Electroencephalography facts for kids
Electroencephalography is a way to record certain patterns of brain activity, on the skin of the head. Nerve cells use electricity to transmit information. It is one of the methods of diagnosis which can be used for conditions that affect the nerves. An electroencephalogram is a recorded electroencephalography. Both are abbreviated EEG. Electroencephalography is used to detect epilepsy, coma, sleep and brain death. Special adaptations exists to research sleep, for example the length of sleep rhythms. Sleep occurs in different phases, the specially adapted EEG can show the length of these phases.
EEG waves
One way that scientists study EEG recordings is by looking at different waves in the EEG. These waves do not move across the body, but occur as changes in the signal at one place over time. They are studied using mathematical techniques for separating a signal into different frequencies. The slowest waves are called delta, and they occur at 1 to 4 cycles per second. Delta occurs in sleep and during anesthesia. The next frequency is called theta, and it occurs at 4 to 8 cycles per second. Theta is seen when a person is trying to keep many different things, such as numbers or words, in memory. It is also seen when a person is drowsy. After theta comes alpha, a wave occurring at 8 to 12 cycles per second. Alpha is seen over the back of the head when a person has his or her eyes shut. It is also seen when a person is resting or meditating. Faster than alpha is beta, a wave that occurs at 12 to 30 cycles per second. It is seen when a person is getting ready to move or no longer resting. It is also seen when a person takes benzodiazepine drugs. Finally, gamma is the fastest wave seen in EEG, occurring at 30 to 100 cycles per second. It is seen when a person is thinking or paying attention to something.
Images for kids
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The first human EEG recording obtained by Hans Berger in 1924. The upper tracing is EEG, and the lower is a 10 Hz timing signal.
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An EEG recording setup
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Computer electroencephalograph Neurovisor-BMM 40 produced and offered in Russia
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Human EEG with prominent alpha-rhythm
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Main types of artifacts in human EEG
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Human EEG with prominent resting state activity – alpha-rhythm. Left: EEG traces (horizontal – time in seconds; vertical – amplitudes, scale 100 μV). Right: power spectra of shown signals (vertical lines – 10 and 20 Hz, scale is linear). Alpha-rhythm consists of sinusoidal-like waves with frequencies in 8–12 Hz range (11 Hz in this case) more prominent in posterior sites. Alpha range is red at power spectrum graph.
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Human EEG with in resting state. Left: EEG traces (horizontal – time in seconds; vertical – amplitudes, scale 100 μV). Right: power spectra of shown signals (vertical lines – 10 and 20 Hz, scale is linear). 80–90% of people have prominent sinusoidal-like waves with frequencies in 8–12 Hz range – alpha rhythm. Others (like this) lack this type of activity.
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Common artifacts in human EEG. 1: Electrooculographic artifact caused by the excitation of eyeball's muscles (related to blinking, for example). Big-amplitude, slow, positive wave prominent in frontal electrodes. 2: Electrode's artifact caused by bad contact (and thus bigger impedance) between P3 electrode and skin. 3: Swallowing artifact. 4: Common reference electrode's artifact caused by bad contact between reference electrode and skin. Huge wave similar in all channels.
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See also
In Spanish: Electroencefalografía para niños
