Lecture: Consciousness
Lecture script · about 15–20 minutes spoken · Week 5
Opening
A nurse rotating onto night shifts fights to stay sharp at the hour his body expects sleep. A long-haul driver wonders whether one more coffee is enough. A student weighs an all-nighter against a full night's sleep before an exam. Each of them is asking what changes your awareness across a day and a night.
That's the subject of this lecture. In Week 1, you learned that mental processes can't be watched directly, so psychologists measure what they can observe. In Week 2, you learned what a correlation can and can't claim. In Week 3, you toured the brain and met the hypothalamus. In Week 4, you followed light into the eye. This week, that light helps set a clock inside your brain. Next week, in Week 6, the course turns to learning.
Here's the plan: what consciousness is, the body clock, the stages of one night, what sleep is for, a sleep claim put to the test, three theories of dreams, and three families of drugs. If you keep one sentence, keep this one: asleep is not off, because your brain changes jobs.
1. Define consciousness: awareness on a dial, not a switch
Think about a lamp with a dimmer instead of an on-off switch. In a lively conversation, you're turned all the way up. Late in a long day, you drift lower. As you fall asleep, you drop lower still. But the lamp never goes fully dark.
That's the idea. 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.
The last part surprises people. A sleeping person seems to have left the room. Yet when researchers record a sleeping brain's electrical activity, it changes all night and never stops.
Here's a quick story to hold it. A child falls asleep at a sleepover while a movie is still playing. She doesn't hear the movie. But when someone says her name, she shifts and mumbles. Her awareness is turned way down, and part of her brain is still listening.
How do researchers know any of this? Awareness can't be seen directly, which was Week 1's lesson about mental processes. So they measure what they can observe, such as brain waves, eye movements, and whether a person responds, and they infer the level of awareness from that.
Pause and try this. Picture a cyclist in traffic, a dozing bus passenger, and a sleeping child who stirs at her name. Who is lowest on the dial, and is anyone at "off"?
Put them in order before you go on.
Here's the answer. The sleeping child is lowest on the dial, and none of the three is at "off," because even a sleeping brain stays active and keeps listening.
2. Keep time: the circadian rhythm, the SCN, and melatonin
You don't need an alarm to feel sleepy late at night. Your body keeps its own time.
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's the clock? It's in the hypothalamus, the small structure you met in Week 3. The suprachiasmatic nucleus, or SCN for short, 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. And 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.
Put the chain together. Light reaches your retina, the story from Week 4. A signal travels to the SCN. As the evening light fades, melatonin rises, and you start to feel sleepy. Morning light tells the SCN that the day has begun.
Now two clocks out of step. A traveler flies east to visit his grandmother, and at local bedtime he's wide awake, because his SCN is still running on home time. A student scrolls a bright phone in bed at midnight, and that light can hold back melatonin. In both cases, the clock is doing its job. It's the light that's out of step with the schedule.
A common belief is that your body clock follows the clock on the wall, or that you can reset it by deciding to. It follows light. That's why a traveler's clock shifts a little each day with local daylight, not the moment the plane lands.
Pause and try this. After the eastward flight, what signal will slowly move the traveler's body clock onto local time, and which part of the brain reads it?
Say the signal and the brain part to yourself.
Here's the answer. Daylight at his destination is the signal, and the SCN in the hypothalamus reads it, shifting his clock a little each day.
3. Walk through one night: the sleep stages
Picture a sleep laboratory. A volunteer sleeps with sensors that record her brain waves, her eye movements, and her muscle tone. It isn't one long, even sleep. It's a sequence of stages, and the sequence repeats.
Sleep comes in two kinds. NREM sleep is non-rapid eye movement sleep, the three stages of a sleep cycle in which the eyes stay mostly still, running from light sleep to the deepest sleep of the night.
Walk through them with the volunteer. First, her brain waves slow, and a door closing down the hall would wake her. That's NREM-1, the lightest stage of sleep, the brief drifting stage right after falling asleep. Next, her brain-wave record shows short bursts of fast activity. Those are sleep spindles, short bursts of fast, rhythmic brain-wave activity that mark the NREM-2 stage of sleep. In NREM-2, she's harder to wake than before. Then her brain waves grow large and slow. That's NREM-3, the deepest stage of sleep, also called slow-wave sleep, in which a person is hardest to wake.
Then something changes. About 90 minutes after she fell asleep, her eyes start to dart, her brain waves look much like waking, and her chin sensor shows her muscles have gone limp. That's 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. After that first REM period, the cycle repeats through the night, NREM stages, then REM, again and again until morning.
Here's the trap to watch for. Many people think REM is the deepest sleep. It's the famous stage, the one with vivid dreams, so "deep" sounds right. But ask two separate questions. How hard is it to wake her? Hardest in NREM-3. How active is her brain? Most active in REM. Deepest and most active are different stages.
Pause and try this. The volunteer's brain waves are large and slow, and she's very hard to wake. Is she in REM sleep or NREM-3?
Ask yourself how hard she is to wake.
Here's the answer. She's in NREM-3, slow-wave sleep, because large, slow waves and being hardest to wake mark the deepest stage, while REM is the most brain-active one.
4. Ask what sleep is for: memory consolidation and how much you need
Imagine two students learning the same 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 those 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: sleep helps consolidate new memories. Week 7 takes memory apart in detail.
So how much sleep is enough? The National Institute of Neurological Disorders and Stroke puts the need for most adults at about 7 to 9 hours a night. Listen to the words "most" and "about." That's a range for a population, not a number every body has to hit.
Two beliefs trip people up here. The first is that sleep is wasted time, so cutting it is a free way to gain hours. But part of the work of keeping what you learned happens while you sleep. The second is that everyone needs exactly 8 hours. The guideline is a range, about 7 to 9 hours, for most adults.
Pause and try this. Someone says, "Sleep is downtime; nothing useful happens." Which idea from this section answers them?
Name the process before you read on.
Here's the answer. Memory consolidation answers them, because sleep is one of the times the brain strengthens and stabilizes new memories so they last.
5. Test a sleep claim: what the sleep and quiz-score data can say
Here's a claim you'll hear everywhere: students who sleep more do better on tests. 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 their hours of sleep the night before a 20-point quiz, and their scores were recorded. This dataset was built for this course to teach with. It's illustrative, not from a real study.
Mean sleep was 7.25 hours, and the mean score was 14.7 points. Now split the group using the 7 to 9 hour guideline. Three students slept fewer than 7 hours, and seven slept 7 to 9 hours. The short-sleep group averaged about 12.3 points out of 20. The 7 to 9 hour group averaged about 15.7. And r, the correlation coefficient, is 0.8457. The sign is positive, so sleep and score rise together. The value is close to 1, so the association is strong. In this sample, students who slept more tended to score higher.
Now the part that matters most. A student who slept more may also have finished studying earlier, had a lighter work schedule, or felt less anxious. Any of those could raise both sleep and score. That's the third-variable problem. And a good day of studying may have made sleep easier, so the arrow could run from preparation to sleep. That's the directionality problem. This is a correlational study. The researchers measured two things and changed nothing. So it supports "associated with," and nothing stronger.
To test "sleep raises scores" as a cause, you'd need an experiment that randomly assigned how long students slept.
Pause and try this. A classmate reads r of 0.8457 and says, "So 84.57 percent of a quiz score comes from sleep." What two mistakes are in that sentence?
Find both mistakes before you go on.
Here's the answer. The correlation coefficient isn't a percentage, and a correlation can't show that sleep causes the score; it shows only that the two are strongly associated in this sample.
6. Compare three theories of dreams: one dream, three readings
Here's a dream you may have had. You're late for an exam in a building you know. The hallway keeps going, the room numbers skip, and the clock won't hold still. You wake up with your heart racing. Why would a brain make that?
There are three major answers in this course, and each one reads the same dream differently.
The first is Freud's, from The Interpretation of Dreams, in 1900. 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. Freud split every dream in two. Manifest content is the story of a dream as the dreamer remembers and tells it: the hallway, the skipping numbers. Latent content is the hidden wish or meaning he believed the remembered story disguised, perhaps a wish to escape a demand.
The second came from Hobson and McCarley in 1977. 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. On this view, a racing heart and a sense of being stuck get stitched into a chase down a hallway, and the story carries no hidden message.
The third is the information-processing view, the view that dreaming is part of how the sleeping brain sorts, connects, and stores the day's experiences and memories. You had an exam coming, the worry was on your mind all day, and so it shows up in the plot.
How do we choose? Use Week 1's test: 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 make claims about brain activity during sleep, and that activity can be measured.
One more trap. People often say dreams happen only in REM sleep. The most vivid dreams do. But some dreaming happens in NREM sleep too, usually less vivid.
Pause and try this. A friend says, "My dream was my brain filing away the stress of the week." Which of the three theories is your friend using?
Match the words "filing away" to a theory.
Here's the answer. That's the information-processing view, because it treats dreaming as the brain sorting and storing the day's experiences.
7. Sort psychoactive drugs: three families and three warning words
Picture two ordinary moments. Before a morning exam, one student orders a double espresso to stay awake. At a party, someone has one drink to relax. Both are taking a psychoactive drug, a chemical substance that changes perception, mood, or awareness by acting on the nervous system. And they're taking drugs from opposite families.
Psychologists sort 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.
Then there are three words for what regular use can do. 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.
Picture a coworker who once felt alert after one energy drink and now needs two for the same lift. That's tolerance.
Now the classic myth. Many people say alcohol is a stimulant, because the first drink can make a person more talkative and less inhibited. Ask what the drug does to the nervous system. Alcohol slows it, including reaction time and judgment. Feeling less inhibited is part of that slowing, not a sign of speeding up.
If you or someone you know is ever worried about a substance, your campus health or counseling office is a confidential place to start.
Pause and try this. The double espresso and the one drink to relax: which family does each drug belong to?
Ask whether each one speeds the nervous system or slows it.
Here's the answer. The espresso's caffeine is a stimulant because it speeds the nervous system up, and the drink's alcohol is a depressant because it slows the nervous system down.
Closing
Let me pull it together. Consciousness is a dimmer, not a switch, and a sleeping brain is never off. Your circadian rhythm runs about 24 hours, and light sets it through the SCN, with melatonin rising as light falls. One night cycles through NREM-1, NREM-2, NREM-3, and REM, with the first REM period about 90 minutes in; NREM-3 is the deepest, and REM is the most active. Sleep helps consolidate memories, and most adults need about 7 to 9 hours. In the sleep and quiz-score data, more sleep is associated with higher scores. Only an experiment could earn the word "cause." A dream can be read as a disguised wish, as a story built from random activity, or as the day being filed. And drugs slow, speed, or distort, with tolerance, dependence, and withdrawal describing what regular use can do.
Next in this module come the slide deck, the Readings and Resources page, the lecture tutorial, the practice set, and the quiz. Next week, in Week 6, the course turns to learning, starting with a dog that learns to expect food.
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