Week 5 · Chapter

Chapter 5 — Consciousness

Introduction to Psychology Free sample edition

The module's primary reading · ~35–45 minutes · Objective 4 (explain how humans sense and perceive the world and how sleep, dreaming, and psychoactive drugs shape states of consciousness), Objective 3 (describe the biological bases of behavior: neurons and neural transmission, the major neurotransmitters, and the structures and functions of the nervous system and brain) · Read it first this week; the lecture, the slides, the tutorial, the quiz, and the Analysis Workshop all build on it.

In plain language

Right now you are aware of these words, the chair under you, and maybe a sound in the next room. That awareness is called consciousness, which means your awareness of yourself and your surroundings, and it rises and falls through every day and night. This week you will learn how your body keeps time on a circadian rhythm, which is a daily cycle of alertness and sleepiness, and what your brain does across one night's sleep. You will compare three ideas about why we dream. You will also sort psychoactive drugs, which are chemicals that change awareness by acting on the nervous system, into three families.

Why you already care about this

It is late, and a reading for tomorrow's class is open in front of you. You read the same paragraph three times. The words stop landing. Your head drops, you jerk awake, and twenty minutes have vanished. What happened in those twenty minutes? Did your brain switch off?

It did not. Sleep researchers can watch a sleeping brain, and it is busy all night. About 90 minutes after you fall asleep, it enters a stage where its activity looks much like waking, your eyes dart under closed lids, and your arms and legs go limp. Most adults need about 7 to 9 hours of this every night, and the whole pattern is timed by a clock that runs on a cycle of about 24 hours. Those three numbers come from the National Institute of Neurological Disorders and Stroke (NINDS), and you will use all three this week.

Then there is the coffee you might reach for to stay awake, and the drink someone has "to relax." Both change your awareness, and they change it in opposite directions.

By the end of this chapter you will be able to:

describe consciousness as a continuum and explain why a sleeping brain is never "off";
explain how the suprachiasmatic nucleus and melatonin keep the circadian rhythm in step with light, and apply that to jet lag and night shifts;
name the four sleep stages in order, say what marks each one, and explain why NREM-3, not REM, is the deepest sleep;
interpret the sleep and quiz-score correlation as an association, naming a third variable and the directionality problem;
compare three theories of dreaming on one dream, and sort a psychoactive drug into its family using the words tolerance, dependence, and withdrawal.

Carry this sentence with you: asleep is not off — your brain changes jobs.

Where we are

Already covered: Week 1 showed that mental processes must be inferred; Week 2 taught what a correlation can claim; Week 3 toured the brain; Week 4 showed how perception is built.
This week: what it means to be aware, how a daily clock times your sleep, what happens across one night, why we might dream, and how three families of drugs change awareness.
How they connect: the body clock sits in Week 3's hypothalamus, and this week's sleep data get Week 2's "how do we know?" questions.
Where we're going next: Week 6, Learning, asks how experience changes behavior, starting with the dogs that learned to expect food.

Each earlier week hands you a tool. In Week 1 you learned that a mental process cannot be watched directly, so psychologists measure what they can observe; sleep researchers do exactly that with brain waves and eye movements. In Week 2 you met ten students who reported their hours of sleep and their next-day quiz scores, with r (the correlation coefficient) of 0.8457. You will meet them again here. In Week 3 you learned that serotonin is associated with mood and sleep, and that the hypothalamus helps regulate hunger, thirst, body temperature, and the release of hormones. In Week 4 you saw light reach the retina. This week, that same light helps set your body's clock.

1. Define consciousness: awareness on a dial, not a switch

Think of a lamp with a dimmer, not a lamp with an on-off switch. At noon in a lively conversation, you are turned all the way up. Late in a long lecture, you drift lower. Falling asleep, you drop lower still. Even then, the lamp never goes fully dark.

Psychologists define it this way:

Consciousness is awareness of yourself and your surroundings. It runs on a continuum from fully alert, through drowsy, to asleep, and the brain stays active at every point on it.

That last clause is the surprise for most people. A sleeping person seems to have left the room. Yet researchers who record the electrical activity of a sleeping brain see it change all night, never stop. Some of that activity looks almost like waking.

Worked example — three moments on the dial. Place each moment on the continuum, from most alert to least.

A cyclist threading through traffic. She tracks cars, signals, and her own speed at once. This is high alertness.
A passenger dozing on a long bus ride. He half hears the driver call his stop and stirs. This is drowsy awareness, low but not gone.
A child asleep at a sleepover. She does not hear the movie still playing. Yet she shifts when someone says her name. Even asleep, her brain keeps listening.

In words: the three moments sit at three points on one dial, and none of them is "off."

Misconception check. Students often think sleep means the brain shuts down, like a computer powering off. It is tempting because a sleeping person does not answer, move much, or remember the night. The cure is the evidence from sleep research: the brain stays active all night, and in one stage its activity looks much like waking. Sleep is a different state of consciousness, not the absence of a brain at work.

An honesty note: "awareness" is hard to measure directly, which is Week 1's lesson about mental processes. Researchers measure what they can observe, such as brain waves, eye movements, and whether a person responds. Then they infer the level of awareness.

Memory hook: a dimmer, not a switch.

2. Keep time: the circadian rhythm, the SCN, and melatonin

You do not need an alarm to feel sleepy late at night. Your body keeps its own time. If you have ever flown across several time zones, you have felt that clock argue with the one on the wall.

The circadian rhythm is the body's internal cycle of alertness and sleepiness that repeats about every 24 hours and is kept in step with day and night by light.

Where is the clock? It sits in a small cluster of neurons in the hypothalamus, the brain region you met in Week 3.

The suprachiasmatic nucleus (SCN) is a small cluster of neurons in the hypothalamus that receives light information from the eyes and keeps the body's circadian rhythm in step with the light-dark cycle.
Melatonin is a hormone whose level rises when light falls in the evening and helps the body start sleep; bright light in the evening holds it back.

So the chain runs like this. Light reaches your retina, the Week 4 story. A signal travels to the SCN. As evening light fades, melatonin rises, and you start to feel sleepy. Morning light tells the SCN that the day has begun.

Worked example — three clocks out of step. For each case, name what the SCN is getting and why the person feels off.

Jet lag. Kwame flies east across several time zones to visit his grandmother. At local bedtime he feels wide awake, because his SCN is still running on home time. Daylight at his destination is the signal that will shift it, a little each day.
A night shift. Ines works overnight stocking shelves at a warehouse and sleeps after sunrise. Her shift asks her to be alert while her body clock signals sleep, and daylight on the drive home tells her SCN that morning has begun.
A late-night screen. Dev scrolls a bright phone in bed at midnight. The light reaching his eyes tells his SCN it is still day, which can hold back melatonin and push his sleepiness later.

In words: in all three cases the clock is doing its job; the light it receives is out of step with the schedule the person is keeping.

Misconception check. Students often think the body clock follows the clock on the wall, or that you can reset it by deciding to. It is tempting because we schedule our lives by the wall clock. The cure is the mechanism: the SCN follows light. That is why a traveler's clock shifts gradually with local daylight rather than the moment the plane lands.

Pause and think. Choose one of these two prompts; they carry equal weight.

(a) Describe a time your sleep schedule moved out of step with your body clock, such as travel, a late shift, or a week of late nights, and explain what light was telling your SCN.
(b) Describe a daily routine that keeps your body clock steady, such as a regular wake-up time or morning daylight, and explain why it works using light and melatonin.

Memory hook: light sets the clock; the wall clock does not.

3. Walk through one night: the sleep stages

Picture a sleep laboratory. A volunteer, Aiyana, sleeps with small sensors on her scalp that record brain waves, sensors near her eyes that record eye movement, and one on her chin that records muscle tone. In the next room, a technician watches the night unfold as a running record. It is not one long, even sleep. It is a sequence of stages that repeats.

Researchers split sleep into two kinds. NREM sleep is non-rapid eye movement sleep, the three stages of a sleep cycle (NREM-1, NREM-2, and NREM-3) in which the eyes stay mostly still, running from light sleep to the deepest sleep of the night. REM sleep is the other kind.

NREM-1 is the lightest stage of sleep, the brief drifting stage right after falling asleep, from which a person is easily woken.
NREM-2 is the stage of sleep that follows NREM-1, marked by sleep spindles, in which a person is harder to wake than in NREM-1.
Sleep spindles are short bursts of fast, rhythmic brain-wave activity that mark the NREM-2 stage of sleep.
NREM-3 is the deepest stage of sleep, also called slow-wave sleep, in which brain waves are large and slow and a person is hardest to wake.
Slow-wave sleep is another name for NREM-3, the deepest sleep stage, named for its large, slow (delta) brain waves.
REM sleep is rapid eye movement sleep, the stage in which the eyes dart, brain activity looks much like waking, the voluntary muscles are temporarily paralyzed, and the most vivid dreams occur.

Worked example — reading Aiyana's first cycle. Follow the technician's record from lights-out.

Drifting off. Aiyana's brain waves begin to slow. A door closing down the hall would wake her easily. This is NREM-1.
Spindles appear. Short bursts of fast activity, the sleep spindles, show up in her brain-wave record. She no longer reacts to small sounds. This is NREM-2.
Large, slow waves. Her brain waves become large and slow, and she would be groggy and hard to wake. This is NREM-3, slow-wave sleep, the deepest stage.
The eyes start to dart. About 90 minutes after she fell asleep, her eye sensors show rapid movements, her brain waves look much like waking, and her chin sensor shows her muscles have gone limp. This is the first REM period.
Again. The cycle then repeats through the night: NREM stages, then REM, again and again until morning.

In words: one night is not one state but a cycle, NREM-1, NREM-2, NREM-3, then REM, with the first REM period arriving about 90 minutes in.

Why are the muscles limp in REM? The voluntary muscles are temporarily paralyzed during REM sleep. That is part of why the most vivid dreams of the night play out without the sleeper acting them out.

Misconception check. Students often think REM is the deepest sleep. It is tempting because REM is the famous stage, the one with vivid dreams, and "deep" sounds like "dreamy." The cure is to separate two questions. How hard is it to wake her? Hardest in NREM-3, so NREM-3 is the deepest sleep. How active is her brain? Most active in REM, where activity looks much like waking. Deepest and most active are different stages.

Memory hook: REM is busy; NREM-3 is deep.

4. Ask what sleep is for: memory consolidation and how much you need

Imagine two students learning the same twenty new words for a language class in the evening. One sleeps a full night. The other stays up late on other work and sleeps far less. Sleep research suggests the first student is likely to hold on to more of the words, and one reason has a name.

Memory consolidation is the process by which a newly formed memory is strengthened and stabilized so it can last; sleep is one of the times the brain does this work.

You met the hippocampus in Week 3, the structure needed to form new declarative memories. This week adds one idea and no more: sleep helps consolidate those new memories. Week 7 will take memory apart in detail.

How much sleep is enough? NINDS puts the need for most adults at about 7 to 9 hours a night. Notice the words "most" and "about." This is a range for a population, not a single number every body must hit.

Misconception check. Students often think sleep is wasted time, downtime when nothing useful happens, so cutting it is a free way to gain hours. It is tempting because you remember almost nothing from a night's sleep. The cure is memory consolidation: some of the work of keeping what you learned happens while you sleep. A second trap is "everyone needs exactly 8 hours." The guideline is a range, about 7 to 9 hours, for most adults.

A caveat: "sleep helps consolidate memories" is a finding about the brain, not a promise about any one night. It does not tell you how many points one extra hour of sleep will add to your quiz. For that kind of claim, you need the next section's habit.

Memory hook: sleep is not downtime; it files the day.

5. Test a sleep claim: what the sleep and quiz-score data can say

Here is the claim you will hear everywhere: "Students who sleep more do better on tests." It sounds true, and section 4 gives a reason it might be. But a psychologist asks Week 2's question first: what design produced this, and what is it allowed to conclude?

You already know the data. Ten students reported how many hours they slept the night before a 20-point quiz, and their scores were recorded. This dataset was constructed for this course to teach with; it is illustrative, not from a real study.

The ten students, from least to most sleep, are shown below.

Hours of sleep and next-day quiz score (out of 20) for ten students, illustrative data
Hours of sleep	5	6	6.5	7	7	7.5	8	8	8.5	9
Quiz score (of 20)	11	14	12	15	13	16	17	14	18	17

Mean sleep is 7.25 hours, and the mean score is 14.7 points.

Worked example — sorting the ten students by the sleep guideline. Use the adult need of about 7 to 9 hours to split the group, compare the two groups, and then decide what you may claim.

Split at 7 hours. 3 students slept fewer than 7 hours (5, 6, and 6.5 hours). 7 students slept 7 to 9 hours (7, 7, 7.5, 8, 8, 8.5, and 9 hours). None slept more than 9 hours. Check: 3 + 7 = 10.
Mean of the short-sleep group. Their scores are 11, 14, and 12. Add them: 11 + 14 + 12 = 37. Divide by the 3 students: 37 ÷ 3 ≈ 12.3 points out of 20.
Mean of the 7-to-9-hour group. Their scores are 15, 13, 16, 17, 14, 18, and 17. Add them: 110. Divide by the 7 students: 110 ÷ 7 ≈ 15.7 points out of 20.
Check the totals. 37 + 110 = 147 points across all ten students, and 147 ÷ 10 = 14.7, the mean score you started with.
Read r (the correlation coefficient). It is 0.8457. The sign is positive, so sleep and score rise together. The value 0.8457 is close to +1, so the linear association is strong.
Say it in words. In this sample, students who slept more tended to score higher. The 7-to-9-hour group averaged about 15.7 points versus about 12.3 for the short-sleep group, a gap of about 3.4 points.

Now the part that matters most. What can a reader conclude from this?

A third variable. A student who slept more may also have finished studying earlier, had a lighter work schedule, or felt less anxious. Any of these could raise both sleep and score. Finishing early, for example, would leave more time for sleep and also mean better preparation.
The directionality problem. A good day of studying may have made sleep easier. Then preparation drives sleep, and sleep is along for the ride.
The design. This is a correlational study: the researchers measured two variables and changed nothing. It supports "associated with" and nothing stronger.

So how would you test "sleep raises scores" as a cause? You would need an experiment: randomly assign students to sleep a set number of hours, keep everything else the same, and compare scores. Random assignment would spread the early finishers and the anxious students evenly across the groups, which no correlation can do.

Misconception check. Students often read r (the correlation coefficient) of 0.8457 as proof that sleep raises scores, or as "84.57 percent." Both are wrong. The tempting part is that the number is large and the story is believable. The cure is Week 2's rule: r is not a percentage, and a correlation does not show a cause. Memory consolidation makes "sleep helps" a reasonable hypothesis. Only an experiment could test it as a cause.

A limitation worth naming: ten students is a very small sample, and these data are illustrative. A real study would need many more people before anyone trusted the size of the gap.

Memory hook: associated with — not caused by — until an experiment says more.

6. Compare three theories of dreams: one dream, three readings

Here is a dream you may have had. You are late for an exam in a building you know. The hallway keeps going, the room numbers skip, and the clock on the wall will not hold still. You wake with your heart racing. Why would a brain produce that?

Psychologists have offered several answers. Three are the major ones for this course. Each one is a different way to read the same dream.

Wish-fulfillment theory is Freud's theory that a dream is a disguised expression of a wish the dreamer is not aware of, so the remembered story hides a deeper meaning.
Manifest content is, in Freud's theory of dreams, the story of a dream as the dreamer remembers and tells it.
Latent content is, in Freud's theory of dreams, the hidden wish or meaning he believed the remembered story disguised.
The activation-synthesis hypothesis is the proposal that dreams are the brain's attempt to build a story out of largely random neural activity generated during REM sleep.
The information-processing view is the view that dreaming is part of how the sleeping brain sorts, connects, and stores the day's experiences and memories.

Freud laid out his theory in The Interpretation of Dreams (1900). Hobson and McCarley proposed activation-synthesis in 1977.

Worked example — the endless hallway, read three ways. Read the dream once per theory.

Wish-fulfillment. The manifest content is the story you remember: the hallway, the skipping numbers, the clock. Freud would look past it for the latent content, a hidden wish the story disguises. A Freudian reading might be a wish to escape a demand you feel you cannot meet, dressed up as a hallway that never ends.
Activation-synthesis. During REM sleep, parts of the brain fire in largely random bursts. The brain does what it always does with signals: it tries to make sense of them. It stitches the bursts into a story, and a racing heart and a sense of being stuck become a chase down a hallway. On this view the story has no hidden message.
Information processing. You have an exam coming, and the worry was on your mind all day. On this view, the dream is part of the brain sorting and storing the day's experiences, so your real concern shows up in the plot.

In words: the same dream is a disguised wish to Freud, a story stitched from random activity to activation-synthesis, and the day being filed to the information-processing view.

How do we know which to believe? Ask Week 1's question: is the claim falsifiable? Freud's latent content can be read into almost any dream, which makes it very hard to test. The other two views make claims about brain activity during sleep, which researchers can measure. That is one reason Freud's theory is much harder to support with evidence than the other two.

Misconception check. Students often think dreams happen only in REM sleep. It is tempting because REM is the dream stage in most summaries, and the most vivid dreams do happen there. The cure is the full finding: some dreaming also happens in NREM sleep, usually less vivid. "Most vivid dreams happen in REM" is accurate; "all dreams happen in REM" is not.

Pause and think. Choose one of these two prompts; they carry equal weight.

(a) Describe a dream you remember, or one you have heard a friend describe, and read it two ways: once as activation-synthesis would, and once as the information-processing view would.
(b) Explain which of the three theories you find most convincing, and name one observation that would count as evidence against it.

Memory hook: one dream — not one meaning.

7. Sort psychoactive drugs: three families and three warning words

Think of two ordinary scenes. Before a morning exam, Lucía orders a double espresso to stay awake and feel sharper. At a party, Tomasz has "one drink to relax." Both are taking a psychoactive drug, and they are taking drugs from opposite families.

A psychoactive drug is a chemical substance that changes perception, mood, or awareness by acting on the nervous system.

Psychologists group these drugs by what they do to the nervous system.

Depressants are psychoactive drugs, such as alcohol, that slow down the activity of the nervous system, including reaction time and judgment.
Stimulants are psychoactive drugs, such as caffeine and nicotine, that speed up the activity of the nervous system and increase alertness.
Hallucinogens are psychoactive drugs that distort perception, changing how a person sees, hears, or experiences the world without an outside stimulus to match.

Three more words describe what can happen when a person uses a drug regularly.

Tolerance is the state in which a larger dose of a drug is needed to produce the same effect a smaller dose once produced.
Dependence is a physical or psychological need for a drug, so that a person feels unable to function normally without it.
Withdrawal is the set of unpleasant physical and psychological symptoms that follows stopping or cutting back a drug a person has come to depend on.

Worked example — sorting four scenes. For each scene, name the drug family and, where it fits, the warning word.

Lucía's double espresso before class. Caffeine speeds up the nervous system, so it is a stimulant.
Tomasz's one drink. Alcohol slows the nervous system, so it is a depressant, and slower reaction time is part of that effect.
A coworker's afternoon energy drinks. Femi once felt alert after one can. Now he needs two cans for the same effect. Needing a larger dose for the same effect is tolerance.
A missed morning coffee. Suppose Mariam drinks coffee every morning, skips it one day, and feels foggy and irritable until lunch. If those unpleasant symptoms follow stopping a drug she has come to depend on, that is withdrawal, and the need behind it is dependence.

In words: sort first by what the drug does to the nervous system, slow, speed, or distort, and then use the three warning words for what regular use can do.

Misconception check. Students often say alcohol is a stimulant. It is tempting because the first drink can make a person feel more talkative and less inhibited. The cure is to ask what the drug does to the nervous system. Alcohol slows it, including reaction time and judgment, so it is a depressant. Feeling less inhibited is part of that slowing, not a sign of speeding up.

An honesty note: this course stays at the level of the three families and the three warning words. It does not rank drugs, give doses, or describe any one substance in detail. If you or someone you know is concerned about a substance, your campus health or counseling office is a confidential place to start.

Memory hook: slow, speed, or distort; then tolerance, dependence, withdrawal.

Key terms

Consciousness — Awareness of yourself and your surroundings. It runs on a continuum from fully alert, through drowsy, to asleep, and the brain stays active at every point on it. (first used: 1. Define consciousness: awareness on a dial, not a switch)
Circadian rhythm — The body's internal cycle of alertness and sleepiness that repeats about every 24 hours and is kept in step with day and night by light. (first used: 2. Keep time: the circadian rhythm, the SCN, and melatonin)
Suprachiasmatic nucleus (SCN) — A small cluster of neurons in the hypothalamus that receives light information from the eyes and keeps the body's circadian rhythm in step with the light-dark cycle. (first used: 2. Keep time: the circadian rhythm, the SCN, and melatonin)
Melatonin — A hormone whose level rises when light falls in the evening and helps the body start sleep; bright light in the evening holds it back. (first used: 2. Keep time: the circadian rhythm, the SCN, and melatonin)
NREM sleep — Non-rapid eye movement sleep, the three stages of a sleep cycle (NREM-1, NREM-2, and NREM-3) in which the eyes stay mostly still, running from light sleep to the deepest sleep of the night. (first used: 3. Walk through one night: the sleep stages)
NREM-1 — The lightest stage of sleep, the brief drifting stage right after falling asleep, from which a person is easily woken. (first used: 3. Walk through one night: the sleep stages)
NREM-2 — The stage of sleep that follows NREM-1, marked by sleep spindles, in which a person is harder to wake than in NREM-1. (first used: 3. Walk through one night: the sleep stages)
Sleep spindles — Short bursts of fast, rhythmic brain-wave activity that mark the NREM-2 stage of sleep. (first used: 3. Walk through one night: the sleep stages)
NREM-3 — The deepest stage of sleep, also called slow-wave sleep, in which brain waves are large and slow and a person is hardest to wake. (first used: 3. Walk through one night: the sleep stages)
Slow-wave sleep — Another name for NREM-3, the deepest sleep stage, named for its large, slow (delta) brain waves. (first used: 3. Walk through one night: the sleep stages)
REM sleep — Rapid eye movement sleep, the stage in which the eyes dart, brain activity looks much like waking, the voluntary muscles are temporarily paralyzed, and the most vivid dreams occur. (first used: 3. Walk through one night: the sleep stages)
Memory consolidation — The process by which a newly formed memory is strengthened and stabilized so it can last; sleep is one of the times the brain does this work. (first used: 4. Ask what sleep is for: memory consolidation and how much you need)
Wish-fulfillment theory — Freud's theory that a dream is a disguised expression of a wish the dreamer is not aware of, so the remembered story hides a deeper meaning. (first used: 6. Compare three theories of dreams: one dream, three readings)
Manifest content — In Freud's theory of dreams, the story of a dream as the dreamer remembers and tells it. (first used: 6. Compare three theories of dreams: one dream, three readings)
Latent content — In Freud's theory of dreams, the hidden wish or meaning he believed the remembered story disguised. (first used: 6. Compare three theories of dreams: one dream, three readings)
Activation-synthesis hypothesis — The proposal that dreams are the brain's attempt to build a story out of largely random neural activity generated during REM sleep. (first used: 6. Compare three theories of dreams: one dream, three readings)
Information-processing view — The view that dreaming is part of how the sleeping brain sorts, connects, and stores the day's experiences and memories. (first used: 6. Compare three theories of dreams: one dream, three readings)
Psychoactive drug — A chemical substance that changes perception, mood, or awareness by acting on the nervous system. (first used: 7. Sort psychoactive drugs: three families and three warning words)
Depressants — Psychoactive drugs, such as alcohol, that slow down the activity of the nervous system, including reaction time and judgment. (first used: 7. Sort psychoactive drugs: three families and three warning words)
Stimulants — Psychoactive drugs, such as caffeine and nicotine, that speed up the activity of the nervous system and increase alertness. (first used: 7. Sort psychoactive drugs: three families and three warning words)
Hallucinogens — Psychoactive drugs that distort perception, changing how a person sees, hears, or experiences the world without an outside stimulus to match. (first used: 7. Sort psychoactive drugs: three families and three warning words)
Tolerance — The state in which a larger dose of a drug is needed to produce the same effect a smaller dose once produced. (first used: 7. Sort psychoactive drugs: three families and three warning words)
Dependence — A physical or psychological need for a drug, so that a person feels unable to function normally without it. (first used: 7. Sort psychoactive drugs: three families and three warning words)
Withdrawal — The set of unpleasant physical and psychological symptoms that follows stopping or cutting back a drug a person has come to depend on. (first used: 7. Sort psychoactive drugs: three families and three warning words)

Summary

Consciousness is awareness on a continuum; a sleeping brain is never off.
The circadian rhythm runs about 24 hours, and light sets it.
The SCN reads light; melatonin rises as light falls and helps start sleep.
A night cycles through NREM-1, NREM-2, NREM-3, and REM.
The first REM period comes about 90 minutes after falling asleep.
NREM-3 is the deepest sleep; REM is the most brain-active.
Sleep helps consolidate memories; most adults need about 7 to 9 hours.
More sleep is associated with higher scores in the sample, which is not proof of a cause.
Dreams: a disguised wish, a story built from random activity, or the day being filed.
Depressants slow, stimulants speed up, hallucinogens distort.
Tolerance, dependence, and withdrawal describe what regular use can do.

Check your understanding

Work these before looking at the answers — they are ungraded, and the answers (with reasoning) are at the bottom of the page.

A nurse, Haruto, switches from day shifts to a run of night shifts. For the first few nights he feels groggy at work in the small hours and cannot fall asleep at noon. Which brain structure and which hormone explain his trouble, and what signal will slowly help his clock adjust?
In a sleep lab, a technician notes that about 40 minutes into the night a volunteer's brain waves are large and slow and she is very hard to wake. About 90 minutes into the night, her eyes begin to dart and her muscles go limp. Name the two stages, and say which is the deepest sleep.
A survey of 40 office workers finds r (the correlation coefficient) = −0.52 between cups of coffee per day and hours of sleep per night. A coworker says, "So coffee steals about half your sleep." Correct the statement: interpret r, then name one third variable and the directionality problem.
Rosa says a glass of wine at dinner is a stimulant because it makes her chatty. Later, she notices she now needs two glasses to feel as relaxed as one used to make her. Sort the drug into its family and name the term for the change she noticed.

Answers (worked reasoning — read after attempting)

The suprachiasmatic nucleus (SCN) and melatonin. Haruto's SCN is still in step with daylight, so at night it signals sleep while he must be alert, and at noon daylight tells it that it is day. Melatonin rises as light falls, so his sleepiness arrives in the middle of his shift. Light is the signal that shifts the clock, so controlling when he sees bright light, such as darkening his room at noon, is what helps it adjust over several days.
The large, slow brain waves and the difficulty waking mark NREM-3, slow-wave sleep. The darting eyes and limp muscles about 90 minutes in mark the first REM period. NREM-3 is the deepest sleep. REM is the most brain-active stage, not the deepest, so the "REM is deepest" trap does not apply here.
The sign is negative, so as cups of coffee go up, hours of sleep tend to go down. A value of 0.52 in size is a moderate association. It is not a percentage, so "half your sleep" misreads it, and it does not show that coffee causes less sleep. A third variable: long work hours could both raise coffee drinking and cut sleep. Directionality: workers who sleep poorly may drink more coffee to get through the day, so poor sleep could drive the coffee.
Alcohol is a depressant: it slows the nervous system, and feeling chatty is part of that slowing of inhibition, not speeding up. Needing two glasses for the effect one used to give is tolerance. Nothing in the scene shows dependence or withdrawal, so those terms do not apply yet.

Next up in this module: the Readings & Resources page, the lecture tutorial, the practice set, and the quiz — and next week, classical conditioning shows the learning rule behind a dog that drools at the sound of a can opener.

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