Sleep and Dreaming — AQA GCSE Psychology Revision Notes

What you'll learn

• The three types of biological rhythm, and which one the sleep cycle belongs to
• How the internal body clock works, and what happens when external cues are removed
• The stages of sleep, and why REM sleep is described as paradoxical
• Two theories of why we sleep, and why they may not actually compete
• Freud's theory of dreaming and the activation synthesis theory
• Insomnia: the difference between primary and secondary, and why worry makes it worse
• Why dreaming is one of the hardest things in psychology to study scientifically

Key terms and definitions

Circadian rhythm — a biological rhythm with a cycle of roughly 24 hours, such as the sleep–wake cycle.

Infradian rhythm — a biological rhythm with a cycle longer than 24 hours, such as the menstrual cycle.

Ultradian rhythm — a biological rhythm with a cycle shorter than 24 hours, such as the cycle of sleep stages.

Zeitgeber — an external cue, principally light, that resets the internal body clock.

Melatonin — a hormone released in darkness that helps control sleep.

REM sleep — rapid eye movement sleep, the stage in which most vivid dreaming occurs.

EEG — a recording of the brain's electrical activity, used to identify sleep stages.

Restoration theory — the view that sleep allows the body and brain to repair and recover.

Evolutionary theory of sleep — the view that sleep conserved energy and kept animals safe, and so had survival value.

Consolidation — the process by which new learning is stabilised into long-term storage.

Insomnia — a disorder involving difficulty falling or staying asleep.

Primary insomnia — insomnia occurring without another condition causing it.

Secondary insomnia — insomnia resulting from another condition such as pain, depression or medication.

Manifest content — in Freud's theory, the dream as it is remembered and described.

Latent content — in Freud's theory, the hidden unconscious meaning the dream is thought to disguise.

Activation synthesis theory — the view that dreams are the brain's interpretation of random neural activity during REM sleep.

Core concepts

Biological rhythms

Three types are distinguished by cycle length. Circadian rhythms run for about 24 hours — the sleep–wake cycle is the obvious example. Infradian rhythms take longer than 24 hours, such as the menstrual cycle. Ultradian rhythms take less than 24 hours, and the cycle of sleep stages is the one to know: one complete pass takes around 90 minutes, so it repeats several times a night.

The body clock and zeitgebers

The sleep–wake cycle is generated internally, but it is reset daily by external cues called zeitgebers, of which light is by far the most important. Light suppresses melatonin release; darkness permits it.

The decisive evidence comes from isolating people from all time cues. The rhythm does not stop — it continues, but settles slightly longer than 24 hours. This shows two things at once: the clock is internally generated, and it needs external correction to stay aligned with the actual day.

That detail explains two practical phenomena. Jet lag is worse travelling east than west, because travelling east shortens the day and requires the clock to advance, which is harder than the delay needed travelling west — the free-running rhythm already runs long, so delaying it works with the grain. And a bright screen late at night delays sleep onset not merely because the content is engaging but because the light itself is a zeitgeber signalling daytime.

Shift work produces a direct conflict: the worker must sleep when the body clock signals wakefulness and work when it signals sleep. Daylight exposure on the journey home makes it worse. If the clock adjusts slowly and delays more easily than it advances, then rotating shifts forwards rather than backwards, keeping rotations long enough for partial adjustment, and controlling light exposure after a night shift should all reduce the disruption — the research turns a matter of convenience into a design problem with testable answers.

Sleep stages and REM

EEG recordings made sleep stages discoverable. By recording the brain's electrical activity, the changing patterns allow stages to be identified objectively rather than relying on the sleeper's report.

Sleep moves through progressively deeper stages and then into REM sleep, before repeating. Later cycles in the night contain proportionally more REM.

REM is called paradoxical sleep because brain activity resembles that of a waking person and the eyes move rapidly, yet the body's voluntary muscles are effectively paralysed — an active brain in an immobile body. The paralysis is thought to prevent dreams being acted out.

Why do we sleep?

Restoration theory holds that sleep allows the body and brain to repair and recover. The evidence is reasonable: growth hormone is released during deep sleep, tissue repair increases, and people who have exercised heavily or been deprived of sleep show more deep sleep afterwards. The recovery of deep sleep first after deprivation is the strongest part of the case. Its difficulty is explaining why the brain remains so active during REM if the purpose is rest.

Evolutionary theory holds that sleep conserved energy and kept an animal still and hidden during hours when it could neither feed nor defend itself effectively, so it improved survival. Differences in sleep duration between species support this. Its difficulty is explaining why sleep appears physiologically necessary rather than merely useful — animals deprived of it suffer badly.

The two answer different questions — one about mechanism, one about origin — and are better treated as complementary than as rivals.

Sleep also serves consolidation: new learning is stabilised into long-term storage during sleep, which is why losing sleep interrupts the process before learning is secured, and why revising all night is self-defeating.

Theories of dreaming

Freud's theory treats dreams as expressions of unconscious wishes. He distinguished the manifest content — the dream as remembered and described — from the latent content, the hidden meaning it disguises. A dream about missing a train is manifest content; an interpretation of it as anxiety about lost opportunity is the proposed latent content.

Activation synthesis theory offers a biological alternative. Random neural activity occurs during REM sleep, and the brain interprets and synthesises those signals into a story. The dream is a by-product of brain activity rather than a coded message, which explains why dreams are so often disjointed.

Insomnia

Primary insomnia occurs without another condition causing it. Secondary insomnia is a consequence of something else — pain, depression, medication. The distinction matters clinically, because secondary insomnia is treated by addressing the underlying cause.

A self-sustaining mechanism keeps insomnia going. Anxiety raises physiological arousal, which is incompatible with falling asleep, so the fear of a bad night becomes a cause of one. Breaking that cycle is the aim of psychological treatment.

This is also the argument against relying on medication. Sleeping tablets work quickly and can break an exhausting cycle where sleep loss is itself causing harm — which matters when someone is unsafe at work or acutely distressed. But they can produce dependence and tolerance, they suppress some sleep stages so the sleep obtained is not equivalent, and they do nothing about the worry or the habits maintaining the problem.

Adolescent sleep

The circadian rhythm shifts later during adolescence, so the biological signal for sleep arrives later while the school day stays fixed. The result is chronic sleep loss produced by a mismatch between a changed body clock and an unchanged timetable — which is why later school start times have been trialled rather than simply urging earlier bedtimes.

Worked examples

Example 1: Classifying a rhythm

A complete cycle of sleep stages takes about 90 minutes. Identify the type of biological rhythm and justify your answer. (2 marks)

It is an ultradian rhythm (1), because its cycle is shorter than 24 hours and therefore repeats several times within a single night (1).

Example 2: Explaining a zeitgeber effect

Explain why using a brightly lit phone in bed can delay sleep. (3 marks)

Light acts as a zeitgeber, an external cue that resets the internal body clock (1). Exposure to light suppresses the release of melatonin, the hormone that promotes sleep (1). The body clock therefore receives a signal that it is still daytime, so sleep onset is delayed (1).

Example 3: Applying Freud's theory

Kai dreams he is trapped in a locked room. Using Freud's theory, identify the manifest and latent content. (2 marks)

The manifest content is the dream as Kai remembers it — being trapped in a locked room (1). The latent content would be the underlying unconscious meaning proposed for it, such as feeling unable to escape a situation in his waking life (1).

You are not being asked whether the interpretation is correct — only to apply the distinction.

Example 4: Evaluating a theory of dreaming

Evaluate the activation synthesis theory of dreaming. (6 marks)

The theory is grounded in measurable brain activity during REM sleep rather than in interpretation that cannot be verified, which makes it more scientific than Freud's account (2). It explains the incoherence of many dreams better than a meaning-based theory, since random activity would not produce an orderly narrative (2). However, it may go too far in treating dream content as meaningless, because dreams often draw on a person's genuine concerns, and it cannot easily explain why some dreams are coherent or why particular themes recur (2).

Common mistakes and how to avoid them

Confusing the three rhythm types. Circadian is about 24 hours, infradian is longer, ultradian is shorter. The prefixes are the memory aid: infra below one day in frequency, ultra beyond it.

Saying melatonin is released in light. It is released in darkness; light suppresses it.

Describing REM as the deepest sleep. It is not. It is paradoxical because the brain is active while the body is immobile.

Mixing up manifest and latent content. Manifest is what you remember; latent is the proposed hidden meaning.

Saying restoration theory is simply wrong. It has real supporting evidence. State what it explains and what it struggles with.

Treating restoration and evolutionary theories as mutually exclusive. They answer different questions.

Forgetting the free-running rhythm runs long. This is what explains the east–west jet lag asymmetry, and it is a strong detail to include.

Claiming Freud's theory has no value. It was the first systematic attempt to explain dream content and generated therapeutic practice. Its weakness is that it cannot be falsified, not that it achieved nothing.

Exam technique for Sleep and Dreaming

Use the technical term and then explain it. "Zeitgeber" alone rarely earns the mark; "zeitgeber, an external cue that resets the body clock" does.

For evaluation of Freud, focus on testability. The central criticism is that latent content cannot be independently verified and any dream can be interpreted to fit, so the theory cannot be falsified. That single point, well made, outweighs a list of vaguer objections.

Link mechanism to consequence in applied questions. Shift work, jet lag and screen use all follow the same chain: rhythm disrupted → melatonin affected → sleep timing shifted.

Remember the methodological problem with dream research. Dream content is available only through the sleeper's report, which requires waking them and depends on memory that fades within minutes. The sleep laboratory is itself an unfamiliar environment that alters sleep. Brain activity can be measured objectively, but no instrument can access what the dream was about — the most interesting variable is the least measurable.

Distinguish REM's function from dreaming's function. REM sleep increases after learning and recovers first when selectively lost, which suggests it does something necessary. But showing REM matters is not showing that the experience of dreaming matters. These are separate claims and only the first is well supported.

On sleep deprivation studies, note the ethical limit. Severe deprivation cannot be imposed on humans, so studies are short or use animals, and the effects of stress and fatigue are hard to separate from the loss of sleep itself.

Quick revision summary

• Circadian ≈ 24 hours, infradian longer, ultradian shorter; the sleep cycle is ultradian at about 90 minutes
• Zeitgebers, mainly light, reset the internal clock; melatonin is released in darkness
• Isolated from time cues the rhythm continues but runs slightly over 24 hours
• Eastward jet lag is worse because advancing the clock is harder than delaying it
• EEG made sleep stages objectively identifiable
• REM is paradoxical: active brain, rapid eye movement, paralysed voluntary muscles
• Restoration theory: growth hormone, tissue repair, deep sleep recovers first after deprivation
• Evolutionary theory: energy conservation and safety; explains species differences in sleep duration
• Sleep consolidates new learning into long-term storage
• Freud: manifest content remembered, latent content hidden — untestable, cannot be falsified
• Activation synthesis: dreams are the brain's interpretation of random REM activity
• Primary insomnia stands alone; secondary insomnia follows another condition
• Anxiety about sleeping raises arousal and sustains insomnia by itself
• Adolescent body clocks shift later, colliding with fixed school start times