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from Part I - Basics
Published online by Cambridge University Press: 24 June 2021
Frequency is the number of times a waveform occurs per second (one big square). Rhythms in addition to frequency have characteristic features of location, morphology, reactivity, and state dependence. Frequencies are descriptive; rhythms are diagnostic. Clinically relevant frequency bands include delta (0.5-4 Hz), theta (5-7 Hz), alpha (8-13 Hz), and beta (14-30 Hz).The alpha rhythm is an obligate feature of normal wakefulness, and it has considerable variations. Abnormal alpha rhythm may be slow, asymmetric, or unreactive (Bancaud’s phenomena). Excessive beta is associated with sedative medications. In most normal adults, theta and delta rhythms are limited to drowsiness or sleep; their occurrence during wakefulness may be abnormal.
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