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

CONSCIOUSNESS AND THE SELF

Sleep and Dreams 172 173

Cleaning the brainDuring the day, our brain activity produces by-products that can become toxic if

they build up. Recent studies using mice have shown

that sleep gives the brain

a chance to clean these by-products away. It seems likely that something similar happens in humans, which may explain some of the negative effects sleep deprivation can have on our ability to learn, remember, and manage our emotions.

The dreaming brainScientists do not know why we dream, but they have theories. Dreams might help us process information and emotions encountered during the day and store them in our long-term memory (see pp.138–139). A dream might also be like a rehearsal—our brain is trying out responses to extreme events in safety so we would be prepared if the event happened in real life. This might explain why dreams are often stressful or negative. Another idea is that dreams are merely “screen savers” for the mind, with no real purpose at all.

Activity during REM sleepEmotional brain regions are very active during REM sleep, as is much of the cortex. The frontal lobes, involved in rational thinking, are much less active.

Thalamus delivers signals to cortex

Reticular formation switches between sleep and wakefulness

Hippocampus sends Visual cortex generates imagery

Parietal cortex, which controls awareness of oneself, is inactive new memories to cortex

Areas of prefrontal cortex are inactive,

so reason not

applied to dreams

Amygdala generates

emotions

SLEEP DISORDERSProblems like sleepwalking, sleep talking, and paralysis occur when the brain fails to make a clean shift between sleep states. This leaves part of our brain awake while other parts are sound asleep. When a person sleepwalks, the motor areas of the brain are awake and active, but the conscious awareness and memory areas are asleep. People can even perform complex tasks such as driving while fast asleep.

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There is evidence to suggest that while we sleep, some
of our brain cells shrink, allowing cerebrospinal
fluid to flow more easily between them. The
fluid carries away any waste that has accumulated to the lymphatic ducts,
where it is removed from
the body.

LYMPHATIC

DUCT

BLOOD VESSEL

Astrocytes shrink, allowing fluid through

Flow of

cerebrospinal fluid

Debris swept away by

cerebrospinal fluid

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G

LY

M

PH

AT

IC

SY

STE

M

THE

LONGEST

RECORDED ATTEMPT TO S TAY AWAKE

IS

264 HOURS

Neurons produce debris

Active

Inactive

KEY

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