Source: Chapter 6, Pages 193–212; 217–224, Dr. McGinty
Tags: consciousness, sleep, circadian rhythm, REM, NREM, sleep disorders, psychoactive drugs, neurotransmitters, addiction, tolerance, withdrawal
Difficulty: Intermediate Prerequisites: Chapter 4 (The Biological Mind), particularly the sections on neurotransmitters, the hypothalamus, and the brain's reward pathway (nucleus accumbens).
This chapter covers two related questions: what does it mean to be conscious, and what happens when consciousness changes? The first half deals with sleep, from the brain regions involved in awareness to the stages of sleep, the consequences of sleep deprivation, and common sleep disorders. The second half covers how psychoactive drugs alter consciousness, focusing on tolerance, withdrawal, addiction, and the specific effects and neurotransmitters associated with common drugs. If you can walk through the sleep stages in order, explain what happens during REM vs. deep sleep, and match each drug to its mechanism, you are in good shape.
Consciousness ranges from full alertness to deep sleep and can be altered by drugs. Sleep cycles through stages (light sleep, deep sleep, REM) with each serving different functions. Sleep deprivation impairs cognition, mood, and health. Psychoactive drugs alter consciousness by affecting neurotransmitter systems, and repeated use can lead to tolerance, withdrawal, and addiction.
Consciousness
Awareness of internal and external stimuli. It includes variations in alertness (from wide awake to deeply asleep), awareness of ongoing sensations, and self-awareness (knowing that you are you).
Default mode network
A set of brain regions that become active when you are not focused on an external task, such as during daydreaming, mind-wandering, or self-reflection.
Circadian rhythm
The body's roughly 24-hour biological clock that regulates the sleep-wake cycle, body temperature, hormone release, and other functions. Driven largely by the suprachiasmatic nucleus in the hypothalamus and influenced by light exposure.
Jet lag
The disruption of circadian rhythms caused by rapid travel across time zones. The body's internal clock is out of sync with the local light-dark cycle.
NREM sleep (non-REM sleep)
The sleep stages that do not involve rapid eye movement. Includes light sleep (stages 1 and 2) and deep sleep (stage 3). Characterised by progressively slower brain waves.
REM sleep (rapid eye movement sleep)
A sleep stage characterised by rapid eye movements, vivid dreaming, and near-complete muscle paralysis. Brain activity during REM resembles waking activity.
Deep sleep (slow-wave sleep, stage 3)
The deepest stage of NREM sleep, characterised by large, slow delta waves. Critical for physical restoration, immune function, and memory consolidation.
Sleep deprivation
A state of not getting enough sleep. Consequences include impaired attention, decision-making, emotional regulation, immune function, and increased risk of accidents.
Insomnia
Difficulty falling asleep or staying asleep. Comes in two types: onset insomnia (trouble falling asleep) and maintenance insomnia (trouble staying asleep). Can be treated with sleep hygiene, cognitive-behavioural therapy, and sometimes medication.
Narcolepsy
A sleep disorder involving sudden, uncontrollable episodes of falling asleep during the day. Often triggered by strong emotions.
Cataplexy
A sudden loss of muscle tone while awake, often triggered by strong emotions such as laughter or surprise. Frequently associated with narcolepsy.
Sleep apnea
A breathing-related sleep disorder in which a person repeatedly stops breathing during sleep. Risk factors include obesity, age, and anatomical features of the airway.
Tolerance
The body's decreasing response to a drug after repeated use, requiring larger doses to achieve the same effect.
Withdrawal
Physical and psychological symptoms that occur when a person stops taking a drug their body has adapted to. Symptoms are often the opposite of the drug's effects.
Addiction
A pattern of compulsive drug use despite negative consequences. Characterised by tolerance, withdrawal, loss of control over use, and continued use despite harm.
Psychoactive drug
A substance that alters mood, perception, or behaviour by acting on the brain's neurotransmitter systems.
Consciousness can be understood in three ways:
Variations in alertness: From fully awake and focused to drowsy to deeply asleep.
Awareness of ongoing sensations: Noticing the temperature of the room, the sound of traffic, the feeling of your clothes.
Self-awareness: Recognising yourself as a distinct individual with your own thoughts and experiences.
Brain regions implicated in consciousness include the cerebral cortex (especially the prefrontal cortex) and the thalamus. The default mode network activates when you are not engaged in a specific task, during daydreaming, self-reflection, and mind-wandering.
The circadian rhythm is a roughly 24-hour cycle that regulates sleep, wakefulness, body temperature, and hormone secretion.
It is driven by the suprachiasmatic nucleus (SCN) in the hypothalamus, which receives light signals from the eyes.
Light is the primary external cue (zeitgeber) that keeps the circadian clock synchronised to the environment.
Jet lag occurs when rapid travel across time zones puts the internal clock out of step with local time. Eastward travel is generally harder to adjust to because it requires advancing the clock.
Individual variations exist: some people are natural "morning larks," others are "night owls." These chronotypes have a biological basis.
Sleep cycles through stages in a roughly 90-minute pattern:
Stage 1 (light sleep): Transition between wakefulness and sleep. Easy to wake someone. Theta waves appear.
Stage 2: Slightly deeper sleep. Sleep spindles and K-complexes appear in the EEG. Body temperature drops, heart rate slows.
Stage 3 (deep sleep / slow-wave sleep): Characterised by delta waves. Hardest to wake someone. Critical for physical restoration, immune function, and memory consolidation.
REM sleep: Brain activity resembles wakefulness. Vivid dreaming occurs. Muscles are essentially paralysed (to prevent acting out dreams). Important for emotional regulation and procedural memory.
As the night progresses, deep sleep periods get shorter and REM periods get longer. You spend more time in deep sleep early in the night and more time in REM later.
Deep sleep deprivation: Impairs physical recovery, weakens the immune system, and disrupts growth hormone release.
REM sleep deprivation: Leads to irritability, difficulty concentrating, and problems with emotional regulation. The brain compensates with "REM rebound," spending more time in REM the following night.
General sleep deprivation: Impairs attention, decision-making, reaction time, emotional regulation, and immune function. Increases risk of accidents, obesity, and chronic health conditions.
Dreams occur primarily during REM sleep, though simpler dreams can occur in other stages. Multiple theories attempt to explain dreaming (e.g., wish fulfilment, memory consolidation, random neural activation), and no single theory is universally accepted.
Nightmares vs. sleep terrors: Nightmares occur during REM sleep; you wake up and remember them. Sleep terrors occur during deep sleep (stage 3); the person appears terrified but usually does not remember the episode.
Insomnia: Two types: onset insomnia (difficulty falling asleep) and maintenance insomnia (difficulty staying asleep). Treatments include sleep hygiene practices, cognitive-behavioural therapy for insomnia (CBT-I), and medication.
Narcolepsy and cataplexy: Narcolepsy involves sudden, overwhelming sleepiness. Cataplexy is a sudden loss of muscle tone while awake. Both are often triggered by strong emotions.
Sleep apnea: Repeated pauses in breathing during sleep. Risk factors include obesity, older age, and structural features of the airway. Often treated with CPAP machines.
SIDS (Sudden infant death syndrome): The unexplained death of an apparently healthy infant during sleep.
Restless legs syndrome (RLS): An uncomfortable urge to move the legs, especially at rest, that disrupts sleep.
Why do people use psychoactive drugs? Reasons include stress relief, social pressure, curiosity, self-medication, pleasure seeking, and cultural or religious practices.
General features:
Tolerance: The body adapts to repeated drug exposure, so more of the drug is needed for the same effect.
Withdrawal: When drug use stops, the body reacts with symptoms often opposite to the drug's effects (e.g., stopping a depressant can cause agitation and anxiety).
Addiction is characterised by compulsive use despite negative consequences, loss of control, tolerance, and withdrawal.
Commonly used psychoactive drugs:
For each drug, know its general characteristics and the neurotransmitters it affects:
Marijuana: Affects the endocannabinoid system. Produces relaxation, altered time perception, increased appetite. Can impair memory and coordination.
LSD: A hallucinogen that primarily affects serotonin receptors. Produces vivid perceptual distortions, altered sense of self, and unpredictable experiences.
Caffeine: A stimulant that blocks adenosine receptors (adenosine promotes sleepiness). Increases alertness and can cause dependence with withdrawal symptoms such as headaches.
Nicotine: A stimulant that activates acetylcholine receptors. Highly addictive. Produces temporary alertness and relaxation, but long-term use carries serious health risks.
Cocaine and amphetamines: Stimulants that increase dopamine, norepinephrine, and serotonin activity. Cocaine blocks reuptake of these neurotransmitters; amphetamines stimulate their release. Produce euphoria, increased energy, but carry high addiction risk and cardiovascular dangers.
Methylphenidate (Ritalin): A stimulant used to treat ADHD. Increases dopamine and norepinephrine in the prefrontal cortex, improving focus and attention at therapeutic doses.
MDMA (Ecstasy): Primarily increases serotonin release, along with dopamine and norepinephrine. Produces feelings of euphoria, emotional closeness, and increased energy. Can cause dangerous overheating and serotonin depletion.
Opioids: Include heroin, morphine, and prescription painkillers. Mimic endorphins, binding to opioid receptors. Produce pain relief and euphoria. Extremely high addiction potential and risk of fatal overdose through respiratory depression.
Students often think we only dream during REM sleep. Dreaming can occur in other stages too, but REM dreams tend to be the most vivid and narrative.
Students sometimes confuse nightmares with sleep terrors. Nightmares happen during REM (you remember them). Sleep terrors happen during deep sleep (you typically do not remember them).
Students often assume tolerance and addiction are the same thing. Tolerance is one feature of addiction, but someone can develop tolerance (e.g., to caffeine) without meeting the full criteria for addiction.
Students sometimes think "natural" drugs like marijuana are not addictive. Marijuana can produce dependence, tolerance, and withdrawal symptoms.
⚠️ Be able to describe the characteristics of each sleep stage and the order in which they occur across the night.
⚠️ Know the difference between nightmares and sleep terrors, including which sleep stage each occurs in.
⚠️ Understand the consequences of sleep deprivation, and the specific consequences of deep sleep vs. REM deprivation.
⚠️ Be ready to match each psychoactive drug to its associated neurotransmitter(s) and primary effects.
⚠️ Know the definitions of tolerance, withdrawal, and addiction, and how they relate to each other.
⚠️ Understand what the circadian rhythm is and what factors disrupt it.
True or False: Sleep terrors occur during REM sleep. False. Sleep terrors occur during deep sleep (stage 3).
Fill in the blank: The neurotransmitter most associated with cocaine's effects is ________. Dopamine.
True or False: As the night progresses, REM periods get longer. True.
Fill in the blank: ________ is the body's decreased response to a drug after repeated use. Tolerance.
True or False: The default mode network is most active when you are concentrating on a difficult task. False. It is most active during rest, daydreaming, and mind-wandering.
Q: Describe the progression of sleep stages across a typical night.
A: Sleep begins with stage 1 (light sleep), progresses to stage 2, then to stage 3 (deep sleep), and then back up to stage 2 before entering REM sleep. This cycle repeats roughly every 90 minutes. Early in the night, deep sleep periods are longer and REM is shorter. As the night progresses, deep sleep periods shorten and REM periods lengthen.
Q: What is the difference between onset insomnia and maintenance insomnia?
A: Onset insomnia is difficulty falling asleep at the start of the night. Maintenance insomnia is difficulty staying asleep, characterised by waking up during the night or too early in the morning.
Q: A person who regularly drinks several cups of coffee per day suddenly stops. What might they experience, and why?
A: They would likely experience withdrawal symptoms, including headaches, fatigue, irritability, and difficulty concentrating. These occur because the body adapted to the regular presence of caffeine (tolerance developed), and its sudden absence creates a rebound effect as adenosine receptors, no longer blocked, are now flooded.
Q: Explain how cocaine affects neurotransmitter activity in the brain.
A: Cocaine blocks the reuptake of dopamine (and norepinephrine and serotonin) in the synapse. This means the neurotransmitter remains in the synaptic gap longer than usual, prolonging its stimulating effects and producing the characteristic euphoria.
Q: What is REM rebound, and what does it suggest about the importance of REM sleep?
A: REM rebound is the tendency to spend more time in REM sleep following a period of REM deprivation. It suggests that REM sleep serves essential functions (likely including emotional processing and memory consolidation) and that the brain will compensate if it misses out.
Q: How do nightmares and sleep terrors differ?
A: Nightmares occur during REM sleep, involve vivid and often remembered dreams, and the sleeper can typically be woken and comforted. Sleep terrors occur during deep sleep (stage 3), involve intense fear and often screaming or flailing, but the person usually does not wake fully and has no memory of the episode.
The neurotransmitter systems discussed in this chapter (dopamine, serotonin, acetylcholine, endorphins) build directly on Chapter 4's coverage of neural communication. Understanding how drugs alter these systems requires knowing what a synapse is, what reuptake means, and how receptors work. The sleep and circadian rhythm material also connects to the hypothalamus, covered in Chapter 4 as a regulator of basic drives.
Consciousness, alertness, self-awareness, default mode network, circadian rhythm, suprachiasmatic nucleus, SCN, zeitgeber, jet lag, chronotype, NREM sleep, REM sleep, stage 1, stage 2, stage 3, deep sleep, slow-wave sleep, delta waves, theta waves, sleep spindles, K-complexes, REM rebound, sleep deprivation, dreams, nightmares, sleep terrors, insomnia, onset insomnia, maintenance insomnia, narcolepsy, cataplexy, sleep apnea, CPAP, SIDS, restless legs syndrome, psychoactive drugs, tolerance, withdrawal, addiction, dependence, marijuana, endocannabinoid, LSD, serotonin, caffeine, adenosine, nicotine, acetylcholine, cocaine, dopamine, amphetamines, Ritalin, methylphenidate, MDMA, ecstasy, opioids, endorphins, reuptake