Lesson 1.12 · Unit 1 · CED topic 1.5 (part 2)
Why we dream, why we sleep, and sleep disorders
Why do people spend a third of their lives unconscious, and why does the sleeping brain produce vivid, strange stories? Scientists do not have complete answers, but they have well-supported theories, and the exam expects you to know the main ones. This lesson covers the two current theories of dreaming, the two main explanations of why we sleep, the sleep disorders the course names, and what happens to behavior and health when sleep is disrupted. It is also a topic where you will practice making a defensible claim from evidence, which is skill 4.A.
Learning objective.
- 1.5.A. Explain how the sleep/wake cycle affects behavior and mental processes throughout the day and night.
Essential knowledge.
- 1.5.A.4. Theories regarding the structure and function of dreams include activation-synthesis and consolidation theory. Exclusion Statement: The psychoanalytic theory of dreams is outside of the scope of the AP Psychology Exam.
- 1.5.A.5. Memory consolidation and restoration are current theories about why sleep occurs. These theories suggest that sleep is useful for organizing and consolidating memories or restoring depleted resources used throughout a given day.
- 1.5.A.6. Many disorders interrupt healthy sleep, and their effects on waking behavior and health vary. Sleep disruptions can affect physical and cognitive performance during wakefulness. Treating sleep disorders and following regular schedules for sleeping can improve waking performance and overall well-being. Disorders commonly studied in introductory psychology include insomnia, narcolepsy, REM sleep behavior disorder, sleep apnea, and somnambulism. Exclusion Statement: The AP Psychology Exam will only address the listed disorders in EK 1.5.A.6.
Theories of dreaming
Dreams are experiences of images, thoughts, and emotions during sleep, and they occur most often in REM sleep (though they can occur in other stages). Two theories are tested on the exam. (The older psychoanalytic theory that dreams hide wishes is outside the scope of the AP Exam.)
- Activation-synthesis theory, proposed by J. Allan Hobson and Robert McCarley in 1977, says that dreams have a biological origin. During REM sleep, the brain stem fires bursts of random neural signals. This is the activation. The cortex then tries to make sense of the signals by weaving them into a story, using memories and emotions. This is the synthesis. A dream's strange plot is the brain's best attempt to interpret chaotic input, which is why dreams combine odd events and why they often reflect recent experiences and worries.
- Consolidation theory says that dreaming is linked to the memory consolidation that goes on during sleep. The brain replays and sorts the day's experiences, strengthening important memories and discarding others. Dreams may be a conscious by-product of this processing, which is why they often draw on recent events.
The two theories are not necessarily in conflict. Activation-synthesis explains where the content of a dream comes from, and consolidation theory explains what the sleeping brain may be doing with it.
Why do we sleep?
Everyone sleeps, including animals, and long deprivation is deadly in animal studies, so sleep must serve important functions. The exam names two current theories.
- Restoration. Sleep allows the body and brain to repair and restore resources that were used up during the day. Tissue growth and repair, immune function, and the clearing of waste from the brain are all active in sleep, particularly in deep NREM sleep, when growth hormone is released.
- Memory consolidation. Sleep helps organize and consolidate memories: strengthening new learning, moving it into long-term storage, and linking it to existing knowledge. People who sleep after learning tend to remember more than people who stay awake for the same period.
Matthew Wilson and Bruce McNaughton recorded the activity of many individual hippocampal neurons in rats as the rats ran along a track. Different neurons fired as the rat passed different places, producing a pattern for each location. When the researchers later recorded from the same neurons while the rats slept, they found that the neurons fired in the same sequence as when the rats were running the track, as if the rats were replaying the experience.
Reading the research: an animal experiment using recordings (and therefore under animal care review). It supports consolidation, since the hippocampus seemed to replay the day's experience during sleep, but it does not show that this replay is necessary for memory, and the findings in rats must be tested in humans.
Sleep disorders
Many disorders interrupt healthy sleep, and their effects on waking behavior and health vary. The exam names five.
- Insomnia is persistent difficulty falling asleep, staying asleep, or waking too early, with daytime effects such as fatigue, poor concentration, and irritability. Stress, irregular schedules, caffeine, and screens at night all contribute.
- Narcolepsy is a disorder in which a person has sudden attacks of overwhelming sleepiness during the day and may fall asleep in the middle of an activity. People with narcolepsy may drop directly into REM sleep, and some experience sudden loss of muscle tone when excited or laughing.
- REM sleep behavior disorder occurs when the muscle paralysis that normally accompanies REM sleep fails, so the person physically acts out their dreams, by shouting, punching, or kicking, sometimes injuring themselves or a bed partner.
- Sleep apnea is a condition in which breathing repeatedly stops for short periods during sleep, often because the airway is blocked. The sleeper briefly wakes to gasp, usually without remembering it. It causes loud snoring, poor-quality sleep, and daytime sleepiness, and it is linked to heart problems. It is common in people who are overweight, and treated with devices that keep the airway open.
- Somnambulism (sleepwalking) is walking or doing other complex activities while asleep. It happens mostly in children, in deep NREM sleep (stage 3), not during dreaming, and the person usually does not remember it. Compare it with REM sleep behavior disorder, in which the person acts out a dream during REM sleep and may remember the dream.
Effects of sleep disruption, and the benefit of regular sleep
Missing sleep affects both waking performance and health. Sleep-deprived people have slower reaction times, poorer attention, weaker memory, more mistakes in judgment, and more irritability and low mood. They are more likely to be injured in car accidents and are more susceptible to illness. These effects are cumulative. Treating sleep disorders and following regular schedules for sleeping can improve waking performance and well-being. Healthy practices include going to bed and getting up at about the same times, avoiding caffeine late in the day, keeping screens away at night, and keeping the bedroom dark and cool.
Sleep needs vary by age: infants sleep most of the day, children need more than adults, and teenagers need about eight to ten hours. Around puberty the body clock shifts later, so teenagers naturally get sleepy later at night and want to wake later. Because of this, researchers such as Mary Carskadon have argued that very early school start times conflict with teenagers' biology, and some school districts have moved start times later. This is a good example of how cultural norms and circumstances (school schedules, work schedules, and social expectations) interact with biology to affect behavior.
Name the sleep disorder most likely in each case. (a) A man falls asleep without warning at his desk, in the middle of a conversation, several times a day. (b) A woman snores loudly, wakes gasping, and is exhausted all day despite 8 hours in bed. (c) A man is observed kicking and shouting during the night, and later describes a dream in which he was fighting off an attacker. (d) A 9-year-old gets out of bed and walks to the kitchen during deep sleep and remembers nothing in the morning. (e) A woman lies awake for hours most nights, worrying, and is tired and irritable at work.
Step 1, (a) sudden daytime sleep attacks: narcolepsy.
Step 2, (b) loud snoring, gasping, daytime fatigue: sleep apnea.
Step 3, (c) acting out a dream, as the REM paralysis fails: REM sleep behavior disorder.
Step 4, (d) walking during deep NREM sleep with no memory: somnambulism.
Step 5, (e) trouble falling asleep and daytime effects: insomnia.
After a week studying for finals, a student dreams that she is taking a test in a building that turns into her grandmother's kitchen. How would each theory explain it?
Step 1, activation-synthesis: during REM, random signals from the brain stem activate the cortex, and the cortex synthesizes a story from them. It drew on her recent experience (test) and old memories (grandmother's kitchen), which explains why the story is odd, combining unrelated settings.
Step 2, consolidation theory: the brain is replaying and organizing what she studied and her recent experiences during sleep. Dreaming about tests is a side effect of the brain's sorting and storing of that material.
Step 3, the psychoanalytic idea that the dream hides a secret wish is outside the scope of the AP Exam, so it is not required.
A school board is debating whether to move the start time of a high school from 7:30 a.m. to 8:30 a.m. A summary of a study of students at two schools says that, in the school that moved its start time later, students slept on average 45 more minutes on school nights and reported fewer days of daytime sleepiness, while a similar school that did not change start times showed no change. Write a defensible claim and support it.
Step 1, a claim takes a position that can be supported with evidence: "Moving the start time to 8:30 a.m. will improve students' sleep and alertness."
Step 2, evidence: students in the school with the later start gained an average of 45 minutes of sleep and reported less sleepiness, and the comparison school stayed the same.
Step 3, reasoning: teenagers' body clocks run later at puberty (a biological reason), so an earlier start forces them to wake during their body's night, and later starts allow more sleep, which improves alertness and performance. The comparison school helps rule out other explanations such as the time of year.
Step 4, limitations: the sample is two schools, and students reported sleepiness themselves, so the claim should be stated cautiously ("is likely to improve").
- Dream theories: activation-synthesis (random brain stem signals are interpreted by the cortex) and consolidation (dreaming linked to memory processing). The psychoanalytic theory is not tested.
- Why we sleep: restoration and memory consolidation.
- Disorders: insomnia, narcolepsy, REM sleep behavior disorder, sleep apnea, somnambulism (sleepwalking in NREM stage 3). Only these five are tested.
- Sleep loss harms attention, memory, mood, and health; regular schedules help. Teen body clocks shift later.
- Compare activation-synthesis theory and consolidation theory of dreaming in one sentence each.
Show answer
Activation-synthesis: dreams result from the cortex interpreting random neural activity generated by the brain stem during REM sleep. Consolidation: dreams are linked to the brain's processing and storing of memories during sleep.
- Why do researchers think sleep helps memory? Give evidence.
Show answer
Sleep seems to consolidate memories: people who sleep after learning remember more, and rat hippocampal neurons replay the pattern of a previous experience during sleep.
- How is REM sleep behavior disorder different from sleepwalking?
Show answer
In REM sleep behavior disorder the normal paralysis of REM fails and the person acts out a dream (and may remember it). In sleepwalking (somnambulism) the person walks in deep NREM sleep and typically does not remember it.
- A truck driver has loud snoring and many brief awakenings at night and falls asleep at red lights. Name the disorder and explain how it affects waking behavior.
Show answer
Sleep apnea: breathing stops repeatedly, which fragments sleep, producing daytime sleepiness, slowed reactions, and reduced attention.
- Why might teenagers have trouble falling asleep before 11 p.m. and getting up at 6:30 a.m.?
Show answer
Around puberty, the circadian rhythm shifts later (melatonin is released later), so teens are not sleepy until later and need to sleep later in the morning.
- A student claims that "sleep deprivation cannot hurt me because I get by on 4 hours." What evidence would you cite to evaluate this claim?
Show answer
Studies show that reduced sleep slows reaction time, impairs attention and memory, and worsens mood, and people often underestimate their own impairment. Sleep deprivation is also associated with illness and accidents.