Normal variant in EEG

1. By: Mohibullah Fazli kakar

2. • Sharp transients of sawtooth shape (biphasic or triphasic)
occurring over the occipital region of waking subjects
during visual exploration (scanning complex picture),
mainly positive relative to other areas and time locked to
saccadic eye movements.
• Amplitude varies, but is generally below 50 μV. Duration
is 100–250 msec except in 1–3 years that can be up to
400 msec.

3. • Resemble positive occipital sharp transients of sleep
(POSTS) and visual evoked potential. Subjects with
prominent lambda waves also have prominent POSTS.
• In children, highest amplitude and sharpest component
is surface negative in the occipital region.
• Random and isolated waveforms but may be recur at
intervals of 200–500 msec.
• Visual evoked potentials occur in association with
saccadic eye movement.
• Do not occur before 1 year of age.

4. • Most common during the middle years of childhood. The prevalence
of lambda waves between 3 and 12 years of age is about 80%.
• Lambda waves have been described as biphasic or triphasic; their
predominant positive component is preceded and followed by a
negative component.
• Strictly bilateral synchronous although may be asymmetrical on the
two sides. Rarely present only on one side.
• Marked asymmetry indicates an abnormality on the side of lower
amplitude.
• The most important precipitating factor is voluntary scanning eye
movements.
• Lambda wave is attenuated by:
• Darkening room
• Staring at a blank card
• Eye closure

5. • Lambda waves usually occur as random and isolated
waveforms but may recur at intervals of 200–500 msec.
• Accompanied by eye movement and eye blink artifacts.
• Sometimes, especially when present unilaterally, they
may be mistaken for focal abnormalities, but the
distinction can be made by replacing the geometric
image with a blank surface.
• Marked and persistent asymmetry indicates an
abnormality on the side of lower amplitude.

6. • Lambda waves are “sharp transients occurring over the
occipital region of the head of waking subjects during visual
exploration, mainly positive
• relative to other areas and time locked to saccadic eye
movement. Amplitude varies, but is generally below 50 μV.”6
Lambda waves do not occur before 1 year of age and are
• most common during the middle years of childhood. The
prevalence of lambda waves between 3 and 12 years is about
80%. Lambda waves have been described as biphasic or

7. • Triphasic; their predominant positive component is preceded
and followed by a negative component. They may be
asymmetrical on the two sides or may be present only on one
• side. Strictly speaking, they are bilaterally synchronous. The
most important precipitating factor of lambda waves is voluntary
scanning eye movements. Lambda waves usually
• occur as random and isolated waveforms but may recur at
intervals of 200–500 msec as in this EEG page.9 Sometimes,
especially when present unilaterally, they may be mistaken
• for focal abnormalities, but the distinction can be made by
replacing the geometric image with a blank surface

9. • Lambda waves (open arrow) are “sharp transients occurring over
the occipital region of the head of waking subjects
• during visual exploration,” mainly positive relative to other areas and
time locked to saccadic eye movement. Amplitude varies, but is
generally below 50 μV.6 Lambda waves have
• been described as biphasic or triphasic; their predominant positive
component is preceded and followed by a negative component.
They are most commonly seen in children
• aged 2–15 years. They may be asymmetrical, appearing bilaterally,
or may be present only on one side. Strictly speaking, they are
bilaterally synchronous. The most important
• precipitating factor of lambda waves is voluntary scanning eye
movements.9 Note alpha rhythm with eye closure (double arrows)

11. • Lambda waves (A) are “sharp transients occurring over the
occipital region of the head of waking subjects during visual
exploration,” mainly
• positive relative to other areas and time locked to saccadic
eye movement. Amplitude varies, but is generally below 50
μV.6 Lambda waves have been described as biphasic or
• triphasic; their predominant positive component is preceded
and followed by a negative component. They are most
commonly seen in children aged 2–15 years. They may

12. • be asymmetrical on the two sides or may be present only
on one side although are strictly bilateral synchronous.
The most important precipitating factor of lambda waves
is
• voluntary scanning eye movements.9 POSTS (B, sample
from the other EEG), also known as “lambdoid waves”
are usually monophasic, sharply contoured
electropositive waves
• seen mainly during light to moderate levels of sleep.