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Six hours that rest like eight
The compression hypothesis
Deep sleep and REM are the two stages that matter most, because deep sleep is when the body recovers and REM is when the brain does. Light sleep takes up more than half of the night. The hypothesis is that the way people currently sleep is inefficient, and that light sleep can be squeezed down.
Two hours a day
If two hours of light sleep were saved while everything else stayed the same, that would free two hours a day for anything a person wants. Over a lifetime that could add up to decades.
Progress so far
Part of the progress is already visible. Helping someone fall asleep faster and cutting down on tossing and turning both raise the efficiency of a night. The target is a version of sleep in which six hours leave a person more rested than eight hours do now.
Why is light sleep the biggest stage?
In adults, the lightest stage that sleep scoring identifies as N2 takes up roughly half of the night. It features brief bursts of brain activity called sleep spindles and sharp waves called K-complexes. Researchers link spindles to the transfer of new memories into long-term storage. The cycle moves through light, deep, and REM stages roughly every 90 minutes.
How do labs tell sleep stages apart?
A sleep lab records brain waves with electrodes on the scalp, eye movements with sensors near the eyes, and muscle tone with sensors on the chin. Together those readings make up a test called polysomnography. Technicians score the recording in 30-second blocks, assigning each one a stage. Deep sleep shows slow, large waves, while REM shows fast activity like wakefulness plus rapid eye movement.
How is sleep efficiency measured?
Sleep efficiency is the time spent asleep divided by the time spent in bed, expressed as a percentage. Sleep clinicians count tossing, awakenings, and a long wait to fall asleep against it. A figure of 85 percent or higher is commonly treated as normal in sleep medicine. Efficiency drops as awake time in bed rises.
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