Lambda and POSTS are similar morphologically, and have a triangular
shape.They occur posteriorly and symmetrically. POSTS stands for
'positive occipital transients of sleep' and occurs in stage 2 sleep.
Lambda occurs in the awake patient when the eyes stare at blank
surfaces. Both are normal wave forms and can occur singly or in
long or short runs.
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K Complexes occur in sleep when arroused - thus K complexes are
seen with noises or other stimuli especially in stage 2 sleep. The
K complex is often followed by an arrousal response - namely a
run of theta waves of high amplitude. Following this the EEG
shows sleep again or the awake state.
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V waves occur in the parasaggital areas of the two sides and take the
form of sharp waves or even spikes which show in the biparietal
regions(vertex) withphase reversal at the midline in tranverse
montages or at the vertex in front-to-back ones. They are seen
in stage 2 sleep along with spindles, K complexes, POSTS, etc..
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Mu activity is a rhythm in which the waves have a shape
suggestive of a wicket fence with sharp tips and rounded bases.
It may show phase reversal between two channels. The frequency
is generally half of the fast activity present.
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Psychomotor variant is a rare rhythm which appears to be an harmonic
of two or more basic rhythms causing a complex form. As can be seen
it is higher in amplitude than the surround and the waves have a notched
appearance. It is quite assymetrical and is often mistaken for paroxysmal
activity. It is benign. It is also known as
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Fourteen and six activity is most often seen in children and adolescents.
As seen it takes the form of 6 Hz and 14 Hz waves sometimes going in
the same direction(up or down) and in others in opposite directions. It is
typically seen in sleep or drowsiness and is usually seen in monopolar
recordings.
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