You dream mostly in one stage of sleep. What are the others for?

Why do we need sleep?

Sleep is an active state with three big benefits:

• Healthy brain: sleep clears waste from the brain and strengthens the pathways that store new memories.
• Physical repair: in deep sleep the body repairs tissue, builds bone and muscle and supports the immune system.
• Emotional stability: sleep, especially REM, helps you process emotions. After poor sleep people are more irritable and less able to cope.

Four stages, light to deep

• These are non-REM (NREM) stages. With REM sleep they make the five stages of one complete sleep cycle.
• Some sleep scientists now merge stages 3 and 4 into one stage. In the exam, use stages 1 to 4 plus REM.

REM sleep

• REM stands for rapid eye movement: the eyes dart about under closed lids.
• Brain activity is fast and close to waking levels.
• Breathing and heart rate become quicker and less regular.
• The arm and leg muscles are temporarily paralysed, so you can't act out dreams.
• Dreaming happens mostly in REM. Some dreaming also occurs in NREM sleep, but it is usually less vivid.

The sleep cycle

• One sleep cycle: stages 1, 2, 3, 4, back up through 3 and 2, then REM.
• A cycle lasts about 90 minutes, and a night usually has 4 to 5 cycles.
• Early cycles contain the most deep sleep (stages 3 and 4).
• Later cycles contain less deep sleep and longer REM periods; the last one can last up to an hour.

Long flight: your body says 3 a.m. at breakfast. What resets it?

Bodily rhythms

• Your body runs on cycles called biological rhythms.
• A circadian rhythm repeats about every 24 hours. The sleep–wake cycle is one: you feel sleepy at night and alert by day.
• Body temperature also follows a circadian rhythm, lowest in the early morning.

The clock inside you

• An endogenous pacemaker is a body clock that keeps rhythms going without outside cues.
• The main endogenous pacemaker is the suprachiasmatic nucleus (SCN) in the hypothalamus. It receives light information from the eyes.
• As it gets dark, the brain signals the pineal gland to release the hormone melatonin, which makes you sleepy.
• Melatonin levels are high at night and low in the morning.

Cues from outside

• An exogenous zeitgeber ("time-giver") is an environmental cue that resets the body clock daily.
• Light is the most important. Light reaching the eyes stops melatonin release and shifts the clock.
• Others: meal times, alarm clocks, social routines.
• Jet lag and shift work: the clock is out of step with these cues.
• With no zeitgebers, rhythms continue but drift from 24 hours.

Lying awake at 3 a.m.: is it the body, the bedroom or the brain?

What is insomnia?

• Insomnia means regularly having problems sleeping.
• Symptoms: finding it hard to fall asleep, waking in the night and lying awake, waking too early, and still feeling tired, irritable or unable to concentrate during the day.
• Sleep onset insomnia: difficulty getting to sleep. Sleep maintenance insomnia: difficulty staying asleep.

Why do people lie awake?

• Stress and anxiety activate the sympathetic nervous system: heart and breathing speed up and the mind races, so the body is too aroused to sleep.
• The bedroom: noise, light, heat, an uncomfortable bed.
• Lifestyle: late caffeine, a large meal, late gaming, jet lag, shift work.
• Health: pain or illness.
• Evaluation: poor sleep also raises stress, so cause and effect are hard to separate.

Damage to the hypothalamus

• The hypothalamus contains the SCN, the body clock. After SCN damage, people can sleep erratically through day and night, because their sleep–wake cycle no longer follows light and dark.
• It also contains the cells that make hypocretin, which keeps us awake. Damage there (such as injury or a tumour) can cause extreme daytime sleepiness.
• One small brain area can disrupt sleep.

Managing insomnia

• Relaxation techniques (deep breathing, muscle relaxation, meditation) activate the parasympathetic nervous system, slowing heart rate and breathing so sleep comes more easily.
• Sleep hygiene improves the physical environment: blackout blinds, a quiet, cool, tidy room, devices out of sight, the clock turned away.
• This describes what psychologists study, not personal advice. Long-lasting sleep problems are for a GP to assess.

Freud thought every dream is a disguised wish. Disguised from whom?

The unconscious mind

• Freud said most of the mind is unconscious: thoughts, memories and desires you are not aware of.
• Repression pushes disturbing or unacceptable wishes out of the conscious mind into the unconscious.
• Repressed wishes don't disappear. They push to be expressed.
• Freud called dreams "the royal road to the unconscious".

Wish fulfilment: two layers of a dream

• Wish fulfilment: Freud claimed every dream fulfils a wish, often a repressed one.
• In sleep the mind's guard relaxes, so wishes can surface.
• A raw wish would shock the dreamer awake, so it is disguised. Freud called dreams the guardians of sleep.
• Manifest content: the dream as you remember it, its story, people and places.
• Latent content: the hidden meaning underneath, the real wish.

Dreamwork

Dreamwork turns the latent content into the manifest content:

• Condensation: several ideas are squeezed into one image.
• Displacement: a feeling is moved onto a less important person or object.
• Symbolism: the wish appears as a symbol.
• Secondary elaboration: the mind stitches the pieces into a story.

In dream analysis, the therapist works backwards from manifest to latent content.

The problem of subjectivity

• Subjectivity means a judgement is shaped by a person's own views, feelings or expectations.
• Only the analyst decides what the latent content is. Two analysts could find two different wishes in the same dream.
• Freud expected to find childhood sexual wishes, and he found them. The Wolfman disagreed with Freud's interpretation.
• An objective method would give the same result whoever applied it.

Brain busy, body paralysed: why does REM sleep turn into a story?

The brain in REM sleep

• In REM sleep brain activity is close to waking levels, the eyes move rapidly and most vivid dreams happen.
• Hobson and McCarley (1977) proposed the activation-synthesis theory: dreams are a by-product of brain activity in REM sleep.
• Dreams have no hidden message. They come from the brain trying to make sense of its own activity.

Activation

In REM sleep three things happen at once:

• Random activation: neurons in the pons, in the brain stem, fire randomly, sending signals up to the higher brain.
• Sensory blockade: sensory signals are blocked.
• Movement inhibition: signals to the muscles are blocked, so the body is paralysed and can't act out the dream.
• The limbic system is also activated, giving dreams strong emotions such as fear.

Synthesis

• The cerebral cortex receives the random signals and tries to make sense of them.
• It synthesises them, combining them with stored memories into a story: the dream.
• Because the input is random, dreams are often bizarre: sudden scene changes, impossible events, odd mixtures of people.
• Any meaning is added by the cortex as it builds the story, not hidden in advance.

Reductionism and holism

• Reductionism explains behaviour by breaking it into its simplest parts. Activation-synthesis reduces dreams to neurons firing in the pons and cortex.
• Strength: those parts can be measured with EEG and brain scans, so the theory is testable.
• Weakness: it ignores meaning, emotions and the dreamer's life, which may explain why dreams reflect real worries.
• Holism looks at the whole person: brain activity plus experiences and feelings.

Big ideas

• Sleep keeps the brain healthy, repairs the body and supports emotional stability.
• A complete sleep cycle has five stages: stages 1 to 4 (light to deep) and REM, when most dreaming occurs.
• A cycle lasts about 90 minutes and repeats 4 to 5 times a night, with more deep sleep early and more REM later.
• The sleep–wake cycle is a circadian rhythm of about 24 hours, kept going by endogenous pacemakers such as the SCN in the hypothalamus.
• The pineal gland releases melatonin as it gets dark, making you sleepy; levels are high at night and low in the morning.
• Exogenous zeitgebers, above all light, reset the endogenous clock each day.
• Insomnia means regularly having trouble getting to sleep or staying asleep, with tiredness during the day.
• Stress (through the sympathetic nervous system), the bedroom, lifestyle and health can all cause it, often together.
• Application: relaxation calms the nervous system and sleep hygiene improves the bedroom; damage to the hypothalamus can disrupt the body clock and wakefulness.
• Freud: dreams fulfil repressed wishes from the unconscious, disguised by dreamwork so they don't wake you.
• Manifest content is the remembered story; latent content is the hidden wish that dream analysis tries to uncover.
• Freud (1918) interpreted the Wolfman's wolf dream as a repressed childhood memory; the main criticism is subjectivity.
• Activation-synthesis (Hobson and McCarley, 1977): in REM sleep, random activation from the brain stem, sensory blockade and movement inhibition happen together.
• The cortex synthesises the random signals with memories into a story, which is why dreams are often bizarre.
• The pons and limbic system drive activation; Williams et al. (1992) found dreams about twice as bizarre as fantasies; the theory is reductionist.