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Related to alpha activity: alpha rhythm
A type of electrical activity in adults detected by EEG in the posterior brain, which may be abolished with visual stimulation and attenuated by thinking. Alpha rhythm (AR) is seen in relaxed adults with closed eyes; it has a frequency of 8–13 Hz over the occipital lobe and has bihemispheric asynchrony, where the non-dominant hemisphere has a greater wave amplitude. Focal CNS disease is accompanied by focally altered AR, which becomes diffuse in coma.
AR is the EEG pattern that corresponds to the awake state; it is present in most, but not all, normal individuals, and is most consistent and predominant during relaxed wakefulness, particularly with reduction of visual input. AR has a range in each person: the low end is exhibited in drowsiness or sleep and the upper end with alertness. AR also varies with age: it is slower in children and older age groups relative to young and middle-aged adults.
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alpha activitySleep disorders The presence of alpha waves or alpha rhythm in an EEG. See Alpha rhythm.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.