Normal EEG Waveforms Flashcards

Which EEG frequency band is most prominent during deep NREM sleep (stage N3)?

Answer: Delta (0.5–4 Hz)

Stage N3 (slow-wave sleep) is defined by high-amplitude delta waves occupying at least 20% of the epoch.

What is the typical voltage (amplitude) range of normal alpha waves recorded from the scalp?

Answer: 20–200 µV

Alpha waves normally range from about 20 to 200 µV in amplitude when recorded from scalp electrodes.

The 'mu rhythm' seen over the central scalp in a relaxed, awake subject has a frequency overlapping with which other rhythm?

Answer: Alpha

The mu rhythm (8–13 Hz) overlaps the alpha frequency band but is maximal over central (C3/C4) rather than occipital electrodes.

During hyperventilation in a normal adult, what EEG change is expected?

Answer: Increased high-amplitude slow activity

Hyperventilation causes cerebral vasoconstriction and hypocapnia, producing diffuse high-amplitude slow (delta/theta) activity in normal subjects.

Which waveform is considered a normal variant and is characteristically seen at the vertex during stage N1 sleep?

Answer: Vertex sharp wave

Vertex sharp waves (V-waves) are normal, high-amplitude transients maximal at Cz that appear during drowsiness and stage N1 sleep.

Lambda waves in the EEG are best elicited by which condition?

Answer: Active visual scanning of a patterned surface

Lambda waves are positive occipital transients that occur during active visual scanning (saccadic eye movements) of a patterned scene.

In a normal adult EEG, what is the expected effect of opening the eyes on the posterior alpha rhythm?

Answer: Alpha is attenuated or blocked

Eye opening causes alpha blocking (Berger effect), suppressing posterior alpha due to visual cortex activation.