How are normal EEG waveforms defined?

Updated: Oct 09, 2019
  • Author: Roy Sucholeiki, MD; Chief Editor: Selim R Benbadis, MD  more...
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Normal EEG waveforms, like many kinds of waveforms, are defined and described by their frequency, amplitude, and location. [4]

  • Frequency (Hertz, Hz) is a key characteristic used to define normal or abnormal EEG rhythms.

  • Most waves of 8 Hz and higher frequencies are normal findings in the EEG of an awake adult. Waves with a frequency of 7 Hz or less often are classified as abnormal in awake adults, although they normally can be seen in children or in adults who are asleep. In certain situations, EEG waveforms of an appropriate frequency for age and state of alertness are considered abnormal because they occur at an inappropriate scalp location or demonstrate irregularities in rhythmicity or amplitude. [5]

  • Some waves are recognized by their shape, scalp location or distribution, and symmetry. Certain patterns are normal at specific ages or states of alertness and sleep.

  • The morphology of a wave may resemble specific shapes, such as vertex (V) waves seen over the vertex of the scalp in stage 2 sleep or triphasic waves that occur in the setting of various encephalopathies.

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