Difficulty: Intermediate | Prerequisites: Behavioral Neuroscience notes (brain structures, EEG, neurotransmitters)
Consciousness covers a wide sweep: what it means to be aware, how the brain generates waking and sleeping states, what happens during dreams, how brain damage alters consciousness, and how psychoactive drugs change it. The sleep section is particularly detail-heavy (know your stages and their associated brain waves), and the drug section requires you to match each substance to its mechanism and effects.
Consciousness is your awareness of yourself and your environment, and it varies along a continuum from full alertness to deep sleep to coma. The brain generates different patterns of electrical activity (measured by EEG) at each level. Sleep cycles through distinct stages with different brain waves and functions. Disruptions to consciousness range from sleep disorders to drug-altered states to brain damage. Know the sleep stages by their EEG signatures, what each stage does for you, and how the major classes of psychoactive drugs change neural activity.
Consciousness
Awareness of internal states and the external environment. Psychologists study it as variations in alertness, awareness of ongoing sensations, and self-awareness.
Rouge test of self-awareness
A test in which a mark is secretly placed on a child's (or animal's) face. If they look in a mirror and touch the mark on their own face (rather than the mirror), they demonstrate self-recognition. Most children pass by about 18-24 months.
Circadian rhythm
The roughly 24-hour biological cycle that regulates sleep-wake patterns, body temperature, hormone release, and other functions. Driven by an internal clock in the hypothalamus (suprachiasmatic nucleus) and synchronised by external cues.
Zeitgeber
An external time cue that helps reset the internal biological clock each day. Light is the most powerful zeitgeber.
Melatonin
A hormone released by the pineal gland in response to darkness. Promotes sleepiness and helps regulate circadian rhythms.
Beta waves
Fast, low-amplitude brain waves associated with active, alert wakefulness. Also appear during REM sleep.
Alpha waves
Slightly slower, more regular brain waves that appear when you are relaxed, calm, or drowsy with eyes closed. Also associated with daydreaming.
Theta waves
Even slower brain waves characteristic of light sleep (Stage 1 NREM).
Delta waves
The slowest, highest-amplitude brain waves. Dominant during deep sleep (Stages 3 and 4 NREM).
Sleep spindles
Brief bursts of rapid brain-wave activity during Stage 2 NREM sleep. Thought to play a role in memory consolidation.
K-complexes
Sharp, high-amplitude waves during Stage 2 NREM sleep. May serve a protective function by suppressing arousal to minor stimuli.
REM sleep
Rapid eye movement sleep, characterised by beta-wave activity (similar to waking), vivid dreaming, and temporary muscle paralysis (atonia). Also called paradoxical sleep.
Activation-synthesis theory
The theory that dreams result from the brain's attempt to make sense of random neural activity generated in the brainstem during REM sleep.
Insomnia
Difficulty falling asleep (onset insomnia) or staying asleep (maintenance insomnia), despite adequate opportunity to sleep.
Narcolepsy
A sleep disorder characterised by sudden, uncontrollable episodes of sleep during waking hours, sometimes accompanied by cataplexy (sudden loss of muscle tone triggered by emotion).
Sleep apnea
A breathing-related sleep disorder in which the person repeatedly stops breathing during sleep, leading to frequent awakenings and poor sleep quality.
Tolerance
The need for increasingly larger doses of a drug to achieve the same effect, because the body adapts to the drug's presence.
Withdrawal
Physical and psychological symptoms that occur when a person stops taking a drug their body has become dependent on. Symptoms are often the opposite of the drug's effects.
Addiction
Compulsive drug use despite negative consequences. Characterised by tolerance, withdrawal, and an inability to stop. Involves the brain's reward circuitry, particularly dopamine pathways and the nucleus accumbens.
Psychologists study consciousness along several dimensions:
Variations in alertness: from full wakefulness to drowsiness to deep sleep to coma.
Awareness of ongoing sensations: the ability to perceive and respond to stimuli.
Self-awareness: recognising yourself as a distinct entity. Tested in young children and some animals using the rouge test (mirror test).
The cerebral cortex is essential for conscious experience. Damage to large cortical areas can eliminate awareness.
The thalamus relays sensory information to the cortex; disruption here can impair consciousness.
The reticular formation in the brainstem regulates general arousal and sleep-wake transitions.
The default mode network (DMN) is a set of brain regions (including the posterior cingulate cortex and medial prefrontal cortex) that are active during rest, mind-wandering, and daydreaming, rather than during focused external tasks.
Roughly 24-hour cycles governing sleep, wakefulness, body temperature, and hormone release.
Internal factors: the suprachiasmatic nucleus (SCN) in the hypothalamus acts as the master clock.
External factors (zeitgebers): light is the primary zeitgeber. It resets the clock each day.
Major Depressive Disorder with Seasonal Pattern (formerly SAD): a mood disorder linked to reduced light exposure during winter months.
Artificial light and technology: screens emit blue light that can delay melatonin release and shift circadian timing.
Shift Maladaptation Syndrome: difficulties (sleep disruption, fatigue, health problems) experienced by people who work irregular or night shifts.
Time zones and jet lag: crossing time zones forces the circadian clock to resynchronise, causing temporary fatigue and cognitive impairment.
Eating patterns are also regulated by circadian rhythms.
Individual differences: "larks" (morning people) have circadian peaks earlier in the day; "owls" (evening people) peak later.
Beta waves: alert, active thinking.
Alpha waves: relaxed, calm, eyes closed.
Gamma waves: associated with higher-order cognitive processing and binding of information across brain areas.
When your mind wanders, the default mode network becomes active and EEG shows alpha-wave patterns.
Mind-wandering consumes a significant portion of waking life and may serve functions like planning and creative problem-solving.
Sleep cycles through distinct stages, each with a characteristic EEG pattern.
Non-REM (NREM) sleep:
Stage 1: light sleep, easily awakened. EEG shows theta waves. Lasts a few minutes. You may experience hypnagogic hallucinations or a sensation of falling.
Stage 2: slightly deeper. EEG shows sleep spindles (brief bursts of activity) and K-complexes (sharp waves). This is where you spend the largest portion of total sleep time.
Stage 3: deep sleep begins. EEG shows increasing delta waves (slow, high-amplitude).
Stage 4: deepest sleep, dominated by delta waves. Hardest to wake someone. Most physical restoration occurs here.
REM sleep:
EEG resembles waking brain activity (beta waves).
Rapid eye movements, vivid dreaming, and temporary muscle paralysis (atonia), which prevents you from acting out dreams.
Called paradoxical sleep because the brain is highly active while the body is effectively paralysed.
Cycling between stages:
A full sleep cycle (NREM Stages 1 through 4, then back up to REM) takes roughly 90 minutes.
Early in the night, more time is spent in deep NREM (Stages 3 and 4). Later in the night, REM periods grow longer.
NREM Stages 3 and 4 (deep sleep): physical restoration, immune function, growth hormone release, memory consolidation (especially declarative memory).
REM sleep: emotional regulation, procedural and emotional memory consolidation, brain development (particularly in infants, who spend far more time in REM).
Loss of deep NREM sleep: impairs physical recovery, weakens immune response, reduces concentration.
Loss of REM sleep: causes irritability, difficulty with complex tasks, and REM rebound (the body compensates by spending more time in REM on subsequent nights).
Activation-synthesis theory: random brainstem signals during REM are interpreted by the cortex, producing the narrative of a dream. Dreams are the brain's attempt to make sense of noise.
Default mode network involvement: parts of the DMN are active during REM, suggesting overlap between dreaming and waking mind-wandering.
Lucid dreaming: a state in which the dreamer becomes aware that they are dreaming and may exert some control over the dream content.
Nightmares vs. night terrors: nightmares are vivid, frightening dreams during REM (the person wakes up and remembers them). Night terrors occur during deep NREM sleep, involve intense fear and sometimes screaming, but the person usually has no memory of them.
Insomnia: onset insomnia (difficulty falling asleep) and maintenance insomnia (difficulty staying asleep).
Narcolepsy: sudden, irresistible sleep attacks during the day. May include cataplexy (sudden muscle collapse triggered by strong emotions) and sleep paralysis (temporary inability to move when falling asleep or waking up).
Sleep apnea: repeated breathing interruptions during sleep, leading to oxygen drops and frequent awakenings. Often caused by airway obstruction.
Sudden Infant Death Syndrome (SIDS): the unexplained death of an apparently healthy infant during sleep. Risk is reduced by placing infants on their backs to sleep.
Restless Leg Syndrome: an uncomfortable urge to move the legs, especially at rest, that disrupts sleep onset.
Coma: a state of deep unconsciousness from which the person cannot be aroused. No sleep-wake cycles, no response to stimuli.
Vegetative state (VS): the person has sleep-wake cycles and some reflexive responses but shows no signs of awareness or purposeful behaviour. The brainstem functions, but the cortex does not.
Brain death: complete and irreversible cessation of all brain activity, including the brainstem. Legally and medically defined as death.
Near-death experiences: vivid subjective experiences (tunnels of light, out-of-body sensations) reported by some people who come close to death. Likely linked to oxygen deprivation and unusual neural activity, though the topic remains debated.
Seizures: sudden, uncontrolled bursts of electrical activity in the brain. Can range from brief lapses of awareness (absence seizures) to full-body convulsions (tonic-clonic seizures). Epilepsy is a condition defined by recurrent seizures.
Psychoactive drugs alter consciousness by changing neurotransmitter activity at the synapse.
Tolerance: the body adapts, so more of the drug is needed for the same effect.
Withdrawal: when the drug is removed, symptoms appear (often opposite to the drug's effects).
Addiction: compulsive use despite harm. Driven by changes in the brain's reward system, particularly dopamine release in the nucleus accumbens.
Marijuana (THC): binds to cannabinoid receptors. Alters mood, perception, appetite, and memory. Mild hallucinogenic and sedative effects.
LSD: a powerful hallucinogen. Acts primarily on serotonin receptors. Produces vivid distortions of perception and thought.
Caffeine: a stimulant that blocks adenosine receptors (adenosine promotes sleepiness). Increases alertness. Mildly addictive; withdrawal produces headaches and fatigue.
Nicotine: a stimulant found in tobacco. Activates acetylcholine (nicotinic) receptors and triggers dopamine release. Highly addictive.
Cocaine and amphetamines: stimulants that block reuptake of dopamine (and to some extent norepinephrine and serotonin), flooding the synapse with these neurotransmitters. Produce euphoria, increased energy, and heightened alertness. High addiction potential.
Methamphetamine: a particularly potent and long-lasting form of amphetamine. Causes massive dopamine release and is highly neurotoxic with chronic use.
Methylphenidate (Ritalin): a milder stimulant used to treat ADHD. Works by blocking dopamine and norepinephrine reuptake.
MDMA (Ecstasy): has both stimulant and hallucinogenic properties. Increases serotonin, dopamine, and norepinephrine release. Produces feelings of empathy and emotional closeness. Can cause dangerous overheating and serotonin depletion.
Alcohol: a depressant. Enhances GABA activity (inhibition) and suppresses glutamate activity (excitation), slowing neural processing. Impairs judgement, coordination, and memory. Chronic use causes tolerance, dependence, and organ damage.
Opioids (heroin, morphine, oxycodone): bind to endorphin receptors, producing pain relief and euphoria. Extremely addictive. Overdose suppresses brainstem breathing centres, which can be fatal.
Students often think REM sleep is the "deepest" stage. It is not. The deepest sleep is NREM Stages 3 and 4 (delta-wave sleep). REM is paradoxically light in terms of arousal threshold, even though the brain is very active.
"You can catch up on lost sleep in one long night" overstates recovery. REM rebound occurs, but chronic sleep deprivation has cumulative effects that a single recovery night does not fully reverse.
Students sometimes assume all psychoactive drugs are illegal. Caffeine, nicotine, and alcohol are all psychoactive, legal, and widely used.
The idea that you can become addicted to a drug after a single use is generally a myth for most substances, though the reinforcing effects of some drugs (e.g. methamphetamine, opioids) are powerful from the start.
⚠️ Know the EEG signature of each sleep stage (theta for Stage 1, spindles and K-complexes for Stage 2, delta for Stages 3 and 4, beta for REM).
⚠️ Understand the difference between NREM and REM sleep in terms of brain activity, dreaming, and body state.
⚠️ Be able to explain REM rebound and why it happens.
⚠️ Know the distinction between nightmares (REM) and night terrors (deep NREM).
⚠️ Understand tolerance, withdrawal, and addiction, and how they relate to each other.
⚠️ Be able to classify drugs by type (stimulant, depressant, hallucinogen) and name their primary mechanism of action.
⚠️ Know how circadian rhythms are regulated (hypothalamus/SCN internally, light/zeitgebers externally).
True or false: Delta waves are associated with alert, focused wakefulness.
Fill in the blank: The brain waves during REM sleep most closely resemble those of ______ wakefulness.
True or false: Narcolepsy involves difficulty falling asleep at night.
Fill in the blank: ______ is the tendency to need increasing doses of a drug to achieve the same effect.
True or false: Alcohol is classified as a stimulant.
Answers: 1. False (delta waves are the slowest waves, seen in deep NREM sleep; alert wakefulness shows beta waves). 2. Active (beta waves appear in both REM sleep and alert waking). 3. False (narcolepsy involves sudden, involuntary sleep episodes during the day). 4. Tolerance. 5. False (alcohol is a depressant; it enhances GABA and suppresses glutamate).
Q: A student stays up all night studying and then sleeps 10 hours the following night. She reports very vivid dreams. What phenomenon explains this, and why does it happen?
A: REM rebound. After REM deprivation (which occurs with sleep deprivation, since REM periods are longest in the last hours of a normal night's sleep), the brain compensates by entering REM more quickly and spending more time in REM during recovery sleep, producing more vivid and frequent dreams.
Q: How does cocaine produce its euphoric effects at the neural level?
A: Cocaine blocks the reuptake of dopamine (and to some extent serotonin and norepinephrine) at the synapse. This leaves more dopamine available in the synaptic gap, overstimulating the reward pathways (particularly the nucleus accumbens) and producing intense feelings of euphoria and energy.
Q: What is the difference between a coma and a vegetative state?
A: In a coma, the person shows no sleep-wake cycles and cannot be aroused at all. In a vegetative state, the person has sleep-wake cycles and some reflexive behaviours (e.g. eyes may open) but shows no evidence of awareness or purposeful response. The brainstem functions in a vegetative state; the cortex does not.
Q: Explain why night terrors and nightmares are different, including when they occur and whether the person remembers them.
A: Night terrors occur during deep NREM sleep (Stages 3-4), involve intense fear, screaming, and physiological arousal, and the person usually has no memory of the episode. Nightmares occur during REM sleep, are vivid and frightening dreams, and the person typically wakes up and remembers the content.
Q: Light is the primary zeitgeber for circadian rhythms. Through what structure does light information reach the brain's master clock?
A: Light is detected by the retina and signals are sent via the retinohypothalamic tract to the suprachiasmatic nucleus (SCN) in the hypothalamus, which is the brain's internal circadian clock.
Consciousness ties tightly to behavioural neuroscience: the EEG recordings you learned about in that unit are exactly how sleep stages are measured, the hypothalamus drives circadian rhythms, and drug mechanisms depend on neurotransmitter systems (dopamine, serotonin, GABA, glutamate). Sensation and perception also connect, since consciousness determines which sensory inputs reach awareness (attention as a filter) and altered states change how stimuli are perceived.
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