EEG, Sleep Stages & Arousals

For patients who generate a posterior dominant rhythm, score W when this rhythm occupies more than 50% of the epoch.

Posterior dominant rhythm, traditionally called alpha rhythm, is typically occipital, appears with eye closure, and attenuates with eye opening.

When a clear posterior rhythm is absent: Wake can be identified using the AASM eye-movement criteria, including blinks, reading movements, or appropriate irregular rapid eye movements with normal/high chin tone.

Do not label every low-amplitude fast EEG segment REM.

Attenuation of the waking posterior rhythm with low-amplitude mixed-frequency activity, commonly 4–7 Hz.

For a patient who generates a posterior dominant rhythm, the replacement pattern occupies more than 50% of the epoch.

• Slow rolling eye movements.
• Vertex sharp waves.
• Reduced muscle tone compared with wake.

Vertex waves and slow eye movements are not required in every N1 epoch.

In the absence of N3 criteria, look for a sleep spindle or a K complex unassociated with arousal in the first half of the current epoch or the last half of the preceding epoch.

Sleep spindle

Frequency 11–16 Hz; duration ≥0.5 seconds; usually most prominent centrally.

K complex

Clearly defined negative sharp component followed by a positive component. Total duration ≥0.5 seconds; usually most prominent frontally.

Once established, N2 can continue through low-amplitude mixed-frequency EEG without a new spindle or K complex in every epoch, provided no ending/transition rule applies.

A K complex associated with an arousal does not by itself establish N2. A spindle is not an arousal.

Do not automatically change the whole epoch to N1 because an arousal occurred somewhere within it.

All required:

Qualifying slow waves at 0.5–2 Hz AND minimum peak-to-peak amplitude of 75 µV in frontal derivations AND at least 20% of the epoch.

For a 30-second epoch: 20% = 6 seconds of qualifying slow-wave activity.

Count the cumulative qualifying duration; it does not need to be one uninterrupted six-second block.

• Not every wave in the broader delta band qualifies for N3.
• Do not count artifact or pathological slowing as normal sleep slow-wave activity.
• Spindles can still occur during N3.
• A K complex may contribute if it meets the qualifying slow-wave definition.

Definite REM recognition:

• Low-amplitude mixed-frequency EEG.
• Low chin EMG tone.
• Rapid eye movements.

Sawtooth waves may occur, but are not required.

REM may continue without rapid eye movements in every epoch when its continuation criteria remain satisfied.

Low chin tone alone does not establish REM. Low-amplitude EEG alone does not establish REM.

Brief muscle twitches can occur during REM.

REM without atonia requires separate evaluation; increased tone does not automatically prove wake or establish REM behavior disorder.