What are the biological differences in non-rem sleep in stages 1-4?
Answer:
During Stage 1, alpha activity decreases, activation is scarce, and the EEG (electroencephalogram) consists mostly of low voltage, mixed frequency activity, much of it at 3-7 Hz. REMs are absent, but slow rolling eye movements appear. The EMG (electromyogram) is moderate to low.
During Stage 2, against a continuing background of low voltage, mixed frequency activity, bursts of distinctive 12-14 Hz sinusoidal waves called "sleep spindles" appear in the EEG. Eye movements are rare, and the EMG is low to moderate.
During Stages 3 and 4, high amplitude (>75 mV), slow (0.5-2 Hz) waves called "delta waves" appear in the EEG; EOG (electrooculogram) and EMG continue as before. In stage 4, there is a quantitative increase in delta waves so that they come to dominate the EEG tracing.
For the most part, the major differences among Stages 1, 2, 3, and 4 are in their EEG patterns. Although there are some exceptions, the general physiology of these stages is fairly similar.
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