Excerpt from Normal EEG Waveforms

Synonyms, Key Words, and Related Terms: EEG, electroencephalography, EEG pattern, EEG waveform, waveform frequency, alpha waves, beta waves, theta waves, delta waves, K complex, V waves, lambda waves, positive occipital sharp transients of sleep, POSTS, wicket rhythm, mu waves, sleep spindles, rhythm en arceau, benign epileptic transients of sleep, BETS

Please click here to view the full topic text: Normal EEG Waveforms

The electroencephalogram (EEG) is the depiction of the electrical activity occurring at the surface of the brain. This activity appears on the screen of the EEG machine as waveforms of varying frequency and amplitude measured in voltage.

EEG waveforms are generally classified according to their frequency, amplitude, and shape, as well as the sites on the scalp at which they are recorded. The most familiar classification uses EEG waveform frequency (eg, alpha, beta, theta).

Information about waveform frequency and shape is combined with the age of the patient, state of alertness or sleep, and head site to determine significance.

Normal EEG waveforms, like many kinds of waveforms, are defined and described by their frequency, amplitude, and location.

Frequency (Hertz, Hz) is a key characteristic used to define normal or abnormal EEG rhythms.
Most waves of 7.5 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.
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.

Patient education

For excellent patient education resources, visit eMedicine's Procedures Center. Also, see eMedicine's patient education article Electroencephalography (EEG).

Please click here to view the full topic text: Normal EEG Waveforms

We subscribe to the
HONcode principles of the
Health On the Net Foundation

Medicine is a constantly changing science and not all therapies are clearly established. New research changes drug and treatment therapies daily. The authors, editors, and publisher of this journal have used their best efforts to provide information that is up-to-date and accurate and is generally accepted within medical standards at the time of publication. However, as medical science is constantly changing and human error is always possible, the authors, editors, and publisher or any other party involved with the publication of this article do not warrant the information in this article is accurate or complete, nor are they responsible for omissions or errors in the article or for the results of using this information. The reader should confirm the information in this article from other sources prior to use. In particular, all drug doses, indications, and contraindications should be confirmed in the package insert. FULL DISCLAIMER