What are arousals and how do they affect sleep stage scoring?

Updated: Aug 19, 2019
  • Author: Andres A Gonzalez, MD, MMM, FACNS; Chief Editor: Selim R Benbadis, MD  more...
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Arousals are paroxysms of activity (Alpha, Theta or frequency > 16 Hz, but no sleep spindles) lasting 3 seconds or longer with at least 10 seconds of sleep preceding the change. Arousals are used for computation of the arousal index (number of arousals per hour from lights off to lights on. The minimum arousal is simply a paroxysmal burst in the EEG channel, usually to alpha or theta activity. Arousals can be scored during any stage.

If the burst results in alpha activity for greater than 50% of the record, then the epoch is scored as wake. In addition to being recorded as a transition to wakefulness, an arousal is still scored. In this case both an arousal and a transition are scored. Arousals are scored in epochs of wake when 10 seconds of continuous sleep are present. 

Arousal from stage N1 is common and usually represented by a burst of activity on the EEG, EOG, and EMG. For an arousal to be scored during REM, there also must be an increase in the submental EEG for at least 1 second.

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