Difficulty: Introductory | Prerequisites: None
This unit covers the nature of consciousness, the biological rhythms that govern sleep, the architecture of sleep stages, common sleep disorders, and the major classes of psychoactive drugs. It sits early in the course because consciousness is the backdrop against which every other psychological process plays out. You should come in knowing basic brain anatomy (the unit on neuroscience pairs closely with this one). If you skipped the neuroscience material, circle back to neurotransmitters before tackling the drug section here.
Consciousness is your awareness of yourself and your environment, and it varies in depth from full alertness to deep sleep. Sleep cycles through distinct N-REM and REM stages, each with signature brain-wave patterns and functions. Psychoactive drugs alter consciousness by mimicking or blocking neurotransmitter activity, and repeated use can produce tolerance, dependence, and withdrawal.
Consciousness
Your awareness of your own sensations, thoughts, and environment. It includes self-awareness and variations in alertness. Increased activity in the default mode network does not describe consciousness; the default mode network is more active during mind-wandering and rest, not focused awareness.
In simple terms, consciousness is the fact that you know you are reading this sentence right now.
Circadian rhythm
A roughly 24-hour biological cycle, governed by light cues (zeitgebers), that regulates your sleep-wake pattern, hormone release, and body temperature.
Think of it as your body's internal clock that tells you when to feel sleepy and when to feel alert.
Zeitgeber
An external cue (most commonly light) that synchronises your circadian rhythm to the day-night cycle.
In simple terms, it is the environmental signal that resets your internal clock each day.
N-REM sleep (non-rapid eye movement)
The three stages of sleep (Stages 1, 2, and 3) that precede REM sleep. N-REM sleep is when the body does most of its physical repair and memory consolidation begins.
Think of it as the "quiet" sleep, where your eyes are still and brain waves progressively slow.
Stage 2 N-REM
The sleep stage characterised by the appearance of K-complexes and sleep spindles on an EEG. You spend more time in Stage 2 than any other single stage.
In simple terms, this is the stage where your brain produces distinctive bursts of electrical activity (spindles) and sharp waveforms (K-complexes).
Stage 3 N-REM (slow-wave sleep)
The deepest stage of N-REM sleep, dominated by delta waves. This is when the body repairs tissue, strengthens the immune system, and builds bone and muscle.
Think of it as your body's nightly maintenance window.
REM sleep (rapid eye movement)
A sleep stage characterised by beta waves (similar to waking), rapid eye movements, and temporary muscle paralysis. Most vivid dreaming occurs here.
In simple terms, your brain is highly active (almost like being awake) but your body is essentially switched off.
Beta waves
Fast, low-amplitude brain waves associated with alert wakefulness and REM sleep.
Delta waves
Slow, high-amplitude brain waves that dominate Stage 3 N-REM (deep sleep). They appear in Stages 3 and 4 of the older four-stage model.
Sleep terrors
Episodes of intense fear, screaming, or thrashing that occur during N-REM sleep. The person is difficult to wake and usually has no memory of the event.
Think of it as a panic episode that happens in deep sleep, not during dreaming.
Nightmares
Frightening dreams that occur during REM sleep. Unlike sleep terrors, the dreamer can usually be woken and will remember the content.
Sleep apnea
A disorder in which breathing repeatedly stops and starts during sleep, often causing the person to wake up gasping for air.
Insomnia
Persistent difficulty falling asleep, staying asleep, or both, despite having the opportunity to sleep.
Narcolepsy
A disorder marked by sudden, uncontrollable episodes of falling asleep during waking hours.
Tolerance
The need for increasing amounts of a substance to achieve the same effect. Your body adapts to the drug's presence.
In simple terms, one cup of coffee used to wake you up, but now you need two.
Withdrawal
The physical and psychological symptoms that occur when a person stops using a substance they have become dependent on. Symptoms often include headaches, fatigue, irritability, or nausea.
Dependence
A state in which the body has adapted to a substance so that its absence triggers withdrawal symptoms.
Methylphenidate (Ritalin)
A stimulant drug prescribed for ADHD that increases the activity of dopamine and norepinephrine, improving alertness and concentration.
In simple terms, Ritalin is a stimulant that helps people with ADHD focus by boosting key neurotransmitters.
Ecstasy (MDMA)
A psychoactive drug that elevates heart rate, blood pressure, and body temperature, and can cause dehydration and exhaustion. It acts primarily on serotonin.
Consciousness includes awareness of sensations, self-awareness, and variations in alertness.
Increased activity in the default mode network is not a feature of consciousness. The default mode network activates when you are daydreaming or not focused on the external world.
Sleep follows a cyclical pattern: Stage 1 N-REM, Stage 2 N-REM, Stage 3 N-REM, then REM, repeating roughly every 90 minutes.
Stage 1 N-REM: Light sleep, easily awakened, theta waves begin.
Stage 2 N-REM: K-complexes and sleep spindles appear. This is a key identifier on exams.
Stage 3 N-REM: Deep sleep, delta waves dominate. Stages 3 and 4 (in the older model) both feature delta waves.
REM sleep: Beta waves, rapid eye movements, vivid dreams, muscle atonia (paralysis).
Sleep serves multiple functions simultaneously:
Body reparation (tissue repair, immune function)
Increased memory consolidation (N-REM sleep transforms memories into long-term storage)
Brain development
The correct answer when all three are listed is "all of the above."
Sleep terrors occur during N-REM sleep and involve intense fear without dream recall.
Nightmares occur during REM sleep and involve vivid, recalled dream content.
Sleep apnea involves waking up gasping for air due to interrupted breathing.
Shortened daylight in winter can shift the sleep-wake cycle and contribute to depressed mood (seasonal affective disorder).
Stimulants (Ritalin, amphetamines, cocaine) increase nervous system activity, boosting dopamine and norepinephrine.
Ecstasy/MDMA causes elevated heart rate, blood pressure, body temperature, dehydration, and exhaustion.
Tolerance develops with repeated use (needing more of a substance for the same effect).
Withdrawal is what happens when a habitual user stops (headaches, fatigue, irritability).
Students often confuse sleep terrors with nightmares. Sleep terrors happen in N-REM sleep and the person does not recall them. Nightmares happen in REM sleep and are remembered.
Students sometimes think K-complexes and sleep spindles appear in Stage 3. They are the signature features of Stage 2 N-REM.
Tolerance and withdrawal are not the same thing. Tolerance is needing more; withdrawal is the reaction to stopping.
The default mode network being active is not a feature of consciousness. This is a common trick answer.
⚠️ Know which sleep stage features K-complexes and sleep spindles (Stage 2 N-REM). This appears in multiple forms on the exam.
⚠️ Be able to distinguish sleep terrors (N-REM) from nightmares (REM).
⚠️ Know that delta waves appear in Stages 3 and 4 (deep sleep).
⚠️ REM sleep is characterised by beta waves, not delta waves.
⚠️ "All of the above" is correct for benefits of sleep when the options are body reparation, brain development, and memory.
⚠️ Know the difference between tolerance, withdrawal, and dependence.
⚠️ Increased default mode network activity does NOT describe consciousness.
True or False: K-complexes and sleep spindles are found in Stage 3 N-REM sleep. False. They are found in Stage 2 N-REM.
True or False: Sleep terrors occur during REM sleep. False. They occur during N-REM sleep.
Fill in the blank: Needing two cups of coffee to get the same effect you used to get from one is an example of __________. Tolerance.
True or False: N-REM sleep plays a role in transforming memories into long-term memory. True.
True or False: The default mode network being active is a defining feature of consciousness. False.
Q: Which brain wave type characterises REM sleep?
A: Beta waves. REM sleep produces fast, low-amplitude brain waves similar to those seen during alert wakefulness.
Q: A student needs to drink two energy drinks to stay awake for studying, when one used to be enough. What is this called?
A: Tolerance. The body has adapted to the substance, requiring a higher dose for the same effect.
Q: Theresa has upsetting experiences that wake her from N-REM sleep. What is she most likely experiencing?
A: Sleep terrors. Nightmares occur during REM sleep; sleep terrors are the N-REM counterpart and involve intense fear without dream recall.
Q: Joan notices her sleep-wake cycle changes and she becomes depressed at a certain time of year. Which season is most likely?
A: Winter. Reduced daylight disrupts circadian rhythms and is associated with seasonal affective disorder.
Q: Bobby is in hospital with elevated heart rate, blood pressure, body temperature, dehydration, and exhaustion. Which drug is most likely responsible?
A: Ecstasy (MDMA). These are its characteristic physiological effects.
Sleep and memory consolidation connect directly to the Memory unit. Understanding that N-REM sleep helps transfer information to long-term memory explains why cramming the night before (and losing sleep) is counterproductive.
Neurotransmitters covered in the Neuroscience unit (dopamine, norepinephrine, serotonin) reappear here as the targets of psychoactive drugs.
The stress unit revisits circadian disruption: chronic stress can impair sleep quality, which in turn worsens stress responses.
consciousness, sleep stages, N-REM, REM, beta waves, delta waves, theta waves, alpha waves, K-complexes, sleep spindles, Stage 2 sleep, deep sleep, slow-wave sleep, sleep terrors, nightmares, sleep apnea, insomnia, narcolepsy, circadian rhythm, zeitgeber, seasonal affective disorder, psychoactive drugs, stimulants, Ritalin, methylphenidate, MDMA, ecstasy, tolerance, withdrawal, dependence, PSYCH 1100, general psychology, Ohio State