How the Brain Works The Facts Visually Explained by DK (z-lib.org)

CONSCIOUSNESS AND THE SELF

Sleep and Dreams

A not-so-silent night There are four distinct stages

of sleep, and we pass through each stage several times a night. During light sleep, we are easily woken.

It is much harder to wake from deep sleep.

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The stages of sleepDuring the night, we cycle through different sleep stages, moving from light to deep sleep then to rapid eye movement (REM) sleep. Our brain waves, produced by the electrical activity of neurons in the cortex (see p.42), change in each stage. As sleep becomes deeper, the waves become slower (with lower frequency) and more organized. We repeat this sleep cycle every few hours, but the proportions shift; we have more slow-wave sleep at the start of the night and more REM

Sleep and DreamsWhen we are asleep, it may seem like our brains are quietly resting, but they are actually busy processing and storing information that we have learned throughout the day.sleep in the early morning.

Period of wakefulness during night

If woken during REM sleep, we are more likely to remember our dreams

Longest periods of

deep sleep are at beginning of night

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HOW MANY
HOURS OF SLEEP
DO WE NEED A NIGHT?
Most adults need
7–9 hours of sleep a night,
but teenagers and children
(especially babies)
need more.
During level 2 sleep, heart rate and breathing become even
Level 1 is
lightest stage
of sleep
In REM sleep, body is paralyzed, but eyes dart about under eyelids
US_172-173_Sleep_and_dreams.indd 172 20/09/2019 12:38