Lambda waves
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Lambda waves are sharp transients that occur over the occipital region during visual exploration, mainly positive relative to other areas and time locked to saccadic eye movements. They have a biphasic or triphasic shape and vary in amplitude up to 50 亮V. Lambda waves are most common in children aged 3-12 and are precipitated by voluntary eye movements.
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Lambda waves
- 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 亮V. Duration is 100250 msec except in 13 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 200500 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 200500 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 亮V.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 200500 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 亮V.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 215 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 亮V.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 215 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.