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| Courtesy: Johns Hopkins |
Sleep
accounts for one-quarter to one-third of the human lifespan. But what exactly
happens when you sleep?
Before the
1950s, most people believed sleep was a passive activity during which the body
and brain were dormant. “But it turns out that sleep is a period during which the
brain is engaged in a number of activities necessary to life—which are closely
linked to quality of life,” says Johns Hopkins sleep expert
and neurologist Mark Wu, M.D.,
Ph.D. Researchers like Wu are spending many of their waking hours
trying to learn more about these processes and how they affect mental and
physical health. Here is a glimpse into the powerful (often surprising)
findings of sleep researchers—and what they’re still trying to discover about
the science of sleep.
All Sleep
Is Not the Same
Throughout
your time asleep, your brain will cycle repeatedly through two different types
of sleep: REM (rapid-eye movement) sleep and non-REM sleep.
The first
part of the cycle is non-REM sleep, which is composed of four
stages. The first stage comes between being awake and falling asleep. The
second is light sleep, when heart rate and breathing regulate and body
temperature drops. The third and fourth stages are deep sleep. Though REM sleep
was previously believed to be the most important sleep phase for learning and
memory, newer data suggests that non-REM sleep is more important for these
tasks, as well as being the more restful and restorative phase of sleep.
As you cycle
into REM sleep, the eyes move rapidly behind closed lids, and brain
waves are similar to those during wakefulness. Breath rate increases and the
body becomes temporarily paralyzed as we dream.
The cycle
then repeats itself, but with each cycle you spend less time in the deeper
stages three and four of sleep and more time in REM sleep. On a typical night,
you’ll cycle through four or five times.