Stage 2 NREM sleep is associated with Theta waves. It is comprised of a similar wavelength as stage 1, but it introduces sleep spindles and the K-complex, which is a short burst of doubled or tripled amplitude and decreased wavelength.

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Brainwave activity (measured by EEG) changes dramatically across the different stages of sleep. Each sleep stage has associated wavelengths of varying amplitude and frequency.

Brainwave Activity Across Sleep Stages

Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020, April 22). Psychology (2nd ed.). OpenStax. https://openstax.org/books/psychology-2e/pages/1-introduction

OpenStax Psychology (2nd ed.) Textbook

When a person is awake, their brainwave activity (EEG) is characterized by a very close wavelength (high frequency) and a medium amplitude relative to the sleep stages.

Awake Brainwave Activity

Stage 1 NREM sleep is associated with Alpha waves. Its brainwave activity is characterized by a generally uniform wavelength and a relatively low amplitude which doubles and quickly reverts to normal every 2 seconds.

Stage 1 NREM Brainwave Activity

Stage 2 NREM Brainwave Activity

Stage 3 NREM sleep is associated with Delta waves. Its brainwave activity features a more uniform wave with gradually increasing amplitude.

Stage 3 NREM Brainwave Activity

Brainwave activity during REM sleep looks much like that of Stage 2 NREM sleep, but without the presence of K-complexes.

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