EEG: alpha
rhythm
An EEG rhythm with a frequency of 8-13 Hz in
human adults, which is most prominent over the parieto-occipital cortex when the eyes are
closed. The rhythm is blocked by eye opening or other arousing stimuli. It is indicative
of the awake state in most normal individuals. It is most consistent and predominant
during relaxed wakefulness, particularly with reduction of visual input. The amplitude is
variable, but typically is below 50 µV in the adult. The alpha rhythm of an
individual usually slows by 0.5-1.5 Hz and becomes more diffuse during drowsiness. The frequency range also
varies with age; it is slower in children and older age groups relative to young
and middle-aged adults.*
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*Reprinted with permission from: Culebras, Antonio Clinical Handbook
of Sleep Disorders Hardcover © 1996 Butterworth-Heinemann
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