Answer
Answer
In healthy individuals, beta activity commonly can be mildly different (< 35%) in amplitude between the 2 hemispheres, which may be caused by differences in skull thickness. Definite focal, regional, or hemispheric difference (at least 50%) in amplitude may be significant and may suggest either skull defect (side with higher amplitude) or a structural lesion (side with lower amplitude). [7] The amount and voltage of beta activity is enhanced by commonly used sedative medications (benzodiazepines, barbiturates).
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Media Gallery
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A 10-second segment showing a well-formed and well-regulated alpha rhythm at 9 Hz. Note that it is very regular, rhythmic, waxing and waning, and posterior dominant. The contrast between the first and second halves of the page illustrates the reactivity of a normal alpha rhythm, with attenuation upon eye opening.
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Fleeting alpha. At times, as shown here, the alpha rhythm can be identified only in very brief bursts and often immediately after eye closure. If normal in frequency, this is normal.
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This is an example of an alpha rhythm with a wider distribution than is typical. If frequency and reactivity are normal, this is another variation of normal. A similar EEG pattern can be seen in patients in a coma (ie, alpha coma), but in these situations it is usually unreactive.
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This is an example of "slow alpha variant." The patient's alpha rhythm at 12 Hz is seen in the second half of the sample. The first half shows a subharmonic at half that frequency, and this is the "slow alpha variant."
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A sample of awake EEG showing the normal or usual amount of beta activity. As shown here, beta activity is often easier to identify during relaxed wakefulness or early drowsiness.
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Mu rhythm over the left (greater than right) central region. To be absolutely certain that this is a mu rhythm, reactivity should be tested. However, morphology (not absolutely typical but fairly so), frequency, and distribution strongly suggest that this is a mu rhythm.
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An example of a typical normal alpha rhythm, showing clear attenuation upon eye opening (second half of page).
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This is the normal amount of beta activity, frontally predominant, with waxing and waning amplitude.
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Alpha rhythm with somewhat "spiky" or sharply contoured morphology. When fragmented (eg, in drowsiness), this can be misinterpreted as sharp waves.
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