In the depicted Stage 2 NREM EEG row, the general waveform is similar to the Stage 1 NREM waveform, but it includes a K-complex between about 10 and 12 seconds. The K-complex is shown as a brief section with doubled or tripled amplitude and shorter wavelength than the surrounding Stage 2 activity.

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Stage 2 sleep, or NREM2, is a phase characterized by a state of deep relaxation. During this stage, theta waves are the predominant brain activity, but they are punctuated by two distinct features: sleep spindles, which are brief bursts of high-frequency brain waves, and K-complexes, which are high-amplitude patterns of brain activity.

Stage 2 Sleep

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

A sharp, biphasic wave observed by EEG during Stage 2 of NREM sleep. The K complex is associated with activity in the paracentral gyri, thalamus, medial regions of the parietal and frontal lobes, and the superior temporal lobe. Its functions include sleep maintenance and arousal, memory consolidation, and synaptic homeostasis.

K complex

A sleep spindle is a rapid burst of higher-frequency brain waves that appears during Stage 2 NREM sleep and is considered important for learning and memory. Visually, on an EEG graph, a sleep spindle is represented by a brief period of waves with a decreased wavelength and moderately increased amplitude. These sinusoidal bursts of neural activity are linked to the thalamus and neocortex and also contribute to sleep maintenance.

Sleep Spindles

Visual Characteristics of Stage 2 Sleep Waveforms

Based on the technician's observations in the case study, identify the patient's most likely stage of sleep and justify your answer by referencing the specific brainwave patterns described.

Sleep Stage Analysis

A sleep study participant is in a state of deep relaxation. An electroencephalogram (EEG) shows that their brain is producing theta waves, but these are frequently punctuated by both brief, rapid bursts of high-frequency waves and single, large high-amplitude patterns of activity. Which phase of sleep do these combined features characterize?

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