The electroencephalogram (EEG) is the depiction of the electrical task developing at the surface of the brain. This activity appears on the display screen of the EEG machine as wavedevelops of differing frequency and amplitude measured in voltage (specifically microvoltages).

EEG waveforms are mostly classified according to their frequency, amplitude, and form, as well as the sites on the scalp at which they are recorded. The most familiar classification supplies EEG wavedevelop frequency (eg, alpha, beta, theta, and delta). <1, 2, 3>


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Instances of alpha, beta, theta, and also delta electroencephalography frequencies.

Information around waveform frequency and also form is unified via the age of the patient, state of alertness or sleep, and place on the scalp to identify definition.


Normal EEG wavecreates, like many kinds of waveforms, are defined and described by their frequency, amplitude, and place. <4>


Some waves are known by their shape, scalp place or distribution, and also symmeattempt. Certain fads are normal at particular periods or states of alertness and also sleep.


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



The frequencies many brain waves range from are 0.5-500 Hz. However, the adhering to categories of frequencies are the a lot of clinically relevant:


Alpha waves generally are checked out in all age groups however are many common in adults. They take place rhythmically on both sides of the head yet are frequently slightly better in amplitude on the nondominant side, especially in right-handed people. A normal alpha variant is noted once a harmonic of alpha frequency occurs in the posterior head regions. They tfinish to be current posteriorly even more than anteriorly and are especially influential with closed eyes and via relaxation.


Alpha task disshows up commonly via attention (eg, psychological arithmetic, tension, opening eyes). In a lot of instances, it is regarded as a normal wavedevelop.


An abnormal exception is alpha coma, many often caused by hypoxic-ischemic encephalopathy of destructive processes in the pons (eg, intracerebral hemorrhage). In alpha coma, alpha waves are distributed uniformly both anteriorly and posteriorly in patients who are unresponsive to stimuli.


Theta waves usually are checked out in sleep at any type of age. In awake adults, these waves are abnormal if they happen in excess.

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This section identifies some normal wavecreates, consisting of K facility, V waves, lambda waves, positive occipital sharp transients of sleep (POSTS), spindles, mu rhythm, spikes, sharp waves, and particular delta waves (polyphasic and also monophasic shapes).


These waves are known by their form and also develop and secondarily by their frequency. They incorporate waves that might be normal in some settings and also abnormal in others (eg, spikes, sharp waves).


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Example of a K facility.

They have the right to take place throughout the brain and also typically are better in amplitude and more significant in the bifrontal regions.


K complexes sometimes are followed by runs of generalized rhythmic theta waves; the whole facility is termed an arousal burst.


V waves are sharp waves that take place during sleep. They are largest and also a lot of apparent at the vertex bilaterally and also commonly symmetrically.


Often, they take place after sleep disturbances (eg, brief sounds) and, like K complexes, might happen during brief semiarousals.


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Example of either lambda or positive occipital sharp transients of sleep (POSTS).

They take place in the awake patient and are shelp to be a lot of evident as soon as the subject stares at a empty, uniform surface.


POSTS are triangular waves that happen in the bilateral occipital areas as positive (upgoing) waves.

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POSTS occur in resting patients and are shelp to be the majority of obvious in phase 2 of sleep, although they are not uncommon in stage 1.


POSTS are similar if not identical to lambda waves both morphologically and in the occipital circulation.