The second stage of non-rapid eye movement. It is thought that memory formation and even learning occur in this state. It takes up about half of our sleep cycle. Dreams are not common but can occur in this stage.
The brain is still able to process external stimuli. Eye movement decreases further at this stage than N1 sleep. Blood pumping rate, metabolism, and body temperature all decrease in this stage.
Like N1, this stage commonly exhibits theta waves in the brain. This state tends to have the highest frequency of sleep spindles.
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