Dreaming

What it's like

A night, cycle by cycle — and what dreams are actually made of.

A night's sleep

• Every ~90 minutes, Round and round: Sleep cycles through non-REM stages and REM about 4 to 6 times a night.
• Early night, Deep sleep first: The first hours are dominated by deep, slow-wave sleep.
• Toward morning, Dream-heavy: Late sleep holds about three times as much REM as early sleep — which is why morning dreams are the vivid ones.

What dreams are like

• Seeing with your eyes shut: The visual areas that build objects and scenes are active, while the one that takes input from the eyes is quiet.
• Nothing seems strange: Flying, dead relatives, rooms that change — all accepted, because the dorsolateral prefrontal cortex that would object is turned down.
• Big feelings: Emotional areas like the amygdala and anterior cingulate are more active than when you're awake.
• Remixed days: Fragments of recent life, not replays — events turn up the next night or two, and again about a week later.
• Not only in REM: Dreaming happens in non-REM sleep too — in some studies up to 70% of non-REM awakenings yield a dream.
• Gone by breakfast: People who remember lots of dreams differ in brain activity in areas that may help them wake briefly and store them.

What's happening in the brain

A brain that's wide awake in some places and switched off in others. The model lights each one as you read.

Lit up

In REM, the pons, thalamus, both amygdalae and the anterior cingulate are more active. The brainstem, thalamus and limbic areas that shut down in deep sleep switch back on.

Turned down

A large area of dorsolateral prefrontal cortex, parts of the parietal cortex and the precuneus are less active — the brain's fact-checkers are off duty.

Pictures without eyes

The visual areas that build objects and scenes are active, while the primary visual cortex, where input from the eyes arrives, is quieter. You're seeing what the brain makes, not what the eyes send.

Feelings without the stress

The neurons that supply noradrenaline — a stress chemical — almost stop firing in REM. A night of REM was linked to a smaller amygdala response to emotional images seen the day before, and to them feeling less intense.

The body switched off

Circuits in the brainstem generate REM sleep and the paralysis that comes with it. That's why running in a dream doesn't move your legs.

Questions people ask

The things people wonder about sleep and dreams — answered.

When nights get strange

Sleep paralysis, and when acting out dreams is worth a doctor's visit.

Sleep paralysis is waking with the body still switched off for REM. About 7.6% of people have had it at least once — 28% of students. Its hallucinations fall into three kinds: an intruder (a sensed presence, fear, sounds, visions), an incubus (pressure on the chest, trouble breathing) and odd bodily feelings like floating. It's frightening, and it ends.

Acting out dreams

If someone repeatedly punches, kicks or shouts in their sleep, as if acting out dreams, it may be REM sleep behaviour disorder — the paralysis failing. It's worth seeing a doctor: of 1,280 people with it, 73.5% had developed Parkinson's or a related condition after 12 years.

Lucid dreaming

Knowing you're dreaming — and how people learn it.

In a lucid dream you know you're dreaming, and often can steer it. About 55% of people have had one, and about 23% have them at least monthly. Lucid dreamers in REM sleep have even answered experimenters' questions — including simple maths — with eye movements.

The fact-checker wakes up

During lucid dreams, frontal areas that are normally quiet in REM switch back on, making a hybrid of dreaming and waking. The evidence is still thin — mostly small studies.

What helped people learn it

• Wake up after about five hours of sleep, then go back to sleep intending to notice the next dream — lucid dreams rose from about 5% to 16% of nights in a week of practice.
• Falling back asleep quickly, within about 10 minutes, made it more likely to work.
• Expect it to take practice: no technique has been shown to work reliably for everyone.

Check what you know

Four questions about the dreaming brain.

• In a dream, your old school is also an airport, and your gran — who died years ago — is the pilot. It all seems perfectly normal. Why didn't anything seem odd? The dorsolateral prefrontal cortex, which would flag it, is turned down in REM. In REM a large area of dorsolateral prefrontal cortex is less active.
• You wake in the night unable to move, with a sense that someone is in the room and a weight on your chest. What's happening? Sleep paralysis: you've woken while your body is still switched off for REM. A sensed presence and pressure on the chest are classic sleep paralysis experiences, and about 7.6% of people have had it.
• You played a new video game all evening, and as you fell asleep you saw its shapes behind your eyes. What's the brain doing? Replaying what you've just learned — even people who couldn't remember playing saw it. After Tetris, people saw the game as they fell asleep, including amnesic patients who didn't remember playing.
• Your dad has started kicking and shouting in his sleep, as if fighting someone in his dreams. What's worth doing? Getting him to a doctor — it could be REM sleep behaviour disorder. Acting out dreams can mean REM's paralysis is failing, and it's linked to later Parkinson's or a related condition in most people who have it.