# Lecture 7: States of Consciousness: Sleep and Dreams
## Introductory Psychology
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## Learning Objectives
By the end of this lecture, students will be able to:
1. Define consciousness and describe the spectrum of awareness
2. Explain the circadian rhythm and the biological clock
3. Describe the stages of sleep and their associated brain wave patterns
4. Discuss the major theories of why we sleep and why we dream
5. Identify common sleep disorders and their characteristics
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## Lecture Content
### I. Consciousness: Levels of Awareness
Consciousness refers to our awareness of ourselves and our environment. Rather than being a simple on-off switch, consciousness exists along a spectrum of levels. At the highest level is focused awareness, the active, deliberate attention we bring to a task. Automatic processing allows us to carry out routine activities with minimal conscious effort — driving a familiar route, for example. Daydreaming represents a shift of attention away from external tasks to internal thoughts. Altered states, including those induced by hypnosis, meditation, or drugs, modify consciousness in distinctive ways. At lower levels, minimal awareness persists during sleep or under anesthesia, and unconsciousness occurs in coma or deep anesthesia.
Selective attention is the ability to focus on specific stimuli while filtering out others. The cocktail party effect describes our ability to pick out our own name from the background noise of a crowded room. Inattentional blindness, dramatically demonstrated by the famous gorilla study of Simons and Chabris, occurs when people fail to notice an unexpected stimulus because their attention is focused elsewhere. Change blindness is the related failure to detect changes in a visual scene, even when those changes are substantial.
### II. Circadian Rhythms and the Biological Clock
The circadian rhythm is the roughly 24-hour biological cycle that regulates sleep-wake patterns, body temperature, and hormone release. The master biological clock resides in the suprachiasmatic nucleus (SCN) of the hypothalamus, which receives direct input from the retina about ambient light levels. This input allows the SCN to synchronize the internal clock with the external light-dark cycle, a process known as entrainment.
Melatonin, a hormone released by the pineal gland in response to darkness, promotes sleepiness. Its levels peak in the evening and decline in the morning, and its production is suppressed by blue light from screens and artificial lighting. Disruptions to circadian rhythms take several forms: jet lag results from a mismatch between the internal clock and a new time zone; shift work disrupts circadian function through irregular schedules; seasonal affective disorder (SAD) is linked to changes in daylight duration; and adolescents experience a natural sleep phase delay during puberty, shifting toward later sleep and wake times.
### III. Stages of Sleep
Sleep is measured using polysomnography, which combines EEG (brain wave recording), EOG (eye movement tracking), and EMG (muscle tone monitoring). During alert wakefulness, the brain produces beta waves, which are low in amplitude and high in frequency. As a person relaxes, alpha waves — slower and more regular — emerge.
Non-rapid eye movement (NREM) sleep progresses through three stages. Stage N1 is a brief transitional phase lasting one to seven minutes, characterized by theta waves. During this stage, people may experience hypnagogic hallucinations (vivid sensory experiences) and myoclonic jerks (sudden muscle contractions that produce a sensation of falling). Stage N2, which accounts for about 50% of total sleep time, features theta waves punctuated by sleep spindles (brief bursts of rapid brain activity) and K-complexes (large, sharp waves). Sleep spindles have been linked to memory consolidation. Stage N3, also known as deep sleep or slow-wave sleep, is dominated by delta waves — high in amplitude and low in frequency. This is the most restorative stage of sleep: growth hormone is released, and waking someone from this stage is difficult and often disorienting. Parasomnias such as sleepwalking, night terrors, and bedwetting most commonly occur during N3. Deep sleep predominates in the first half of the night and diminishes with age.
REM sleep is sometimes called paradoxical sleep because the brain is highly active — producing EEG patterns resembling wakefulness — while the body is essentially paralyzed through a state called atonia. Vivid, story-like dreams occur most frequently during REM, and the characteristic rapid eye movements appear to reflect dream activity. REM sleep plays important roles in memory consolidation, emotional processing, and learning. As the night progresses, REM periods become longer, and REM rebound — an increase in REM sleep — occurs after periods of REM deprivation. A complete sleep cycle lasts approximately 90 minutes, and most people pass through four to six cycles per night.
A hypnogram showing sleep stages across a typical 8-hour night. The y-axis shows sleep stages (Wake, REM, N1, N2, N3) and the x-axis shows hours of sleep (0-8). The graph shows 4-5 complete sleep cycles, with deep sleep (N3) predominating in the first half and REM periods becoming longer and more frequent in the second half. Beside the hypnogram, small EEG waveform samples are shown for each stage: beta waves for wakefulness, alpha for relaxation, theta for N1-N2 with spindles and K-complexes marked, delta for N3, and desynchronized fast activity for REM.
### IV. Why Do We Sleep?
Several theories address why sleep is necessary. The restoration theory proposes that sleep repairs the body and brain after daily wear. Growth hormone is released during deep sleep, immune function is enhanced, and the glymphatic system clears metabolic waste products such as beta-amyloid from the brain. The energy conservation theory suggests that sleep reduces energy expenditure during periods when activity would be inefficient. The memory consolidation theory holds that sleep strengthens and reorganizes memories: slow-wave sleep appears to consolidate declarative (factual) memories, while REM sleep consolidates procedural and emotional memories, and sleep spindles correlate with memory improvement. The brain development theory notes that REM sleep is especially important for neural development, as evidenced by the fact that infants spend about 50% of their sleep time in REM compared to 20-25% for adults.
Sleep deprivation produces wide-ranging effects, including impaired attention, judgment, reaction time, and memory; increased irritability, anxiety, and depression; weakened immune function; and weight gain due to altered hunger hormones (leptin decreases and ghrelin increases). Microsleeps — brief, involuntary episodes of sleep — can occur during waking hours. Chronic sleep deprivation has been linked to cardiovascular disease, diabetes, and shortened lifespan.
### V. Dreams
Dreams occur throughout the night but are most vivid and story-like during REM sleep; NREM dreams tend to be more thought-like and less elaborate. Dream content is often bizarre and emotionally charged, and may incorporate recent experiences, a phenomenon known as day residue.
Several theories attempt to explain why we dream. Freud's wish fulfillment theory proposed that dreams express unconscious desires and conflicts, distinguishing between the manifest content (the surface storyline) and the latent content (the hidden, symbolic meaning). This theory is largely unfalsifiable and has limited empirical support. The activation-synthesis theory of Hobson and McCarley suggests that random neural activity in the brainstem during REM is interpreted by the cortex, which weaves the random signals into a narrative. Under this view, dreams are essentially meaningless byproducts of neural activity. The information-processing theory proposes that dreams help consolidate memories and process the day's experiences. The cognitive theory, advanced by Domhoff, holds that dreams reflect waking concerns, thoughts, and conceptual knowledge. The threat simulation theory, proposed by Revonsuo, argues that dreaming evolved as a way to rehearse threatening scenarios, thereby enhancing survival.
Lucid dreaming, in which a person becomes aware that they are dreaming while still in the dream state, has been verified through pre-arranged eye movement signals during REM sleep. Some lucid dreamers can exert control over dream content.
A visual comparison of four major theories of dreaming. Panel A: Freud's wish fulfillment — an iceberg metaphor with manifest content above the waterline and latent content below. Panel B: Activation-synthesis — a brainstem generating random neural signals (shown as lightning bolts) that travel to the cortex, which constructs a dream narrative. Panel C: Information-processing — a filing cabinet metaphor with memories being sorted and consolidated during sleep. Panel D: Threat simulation — a dreaming person encountering a predator, illustrating the evolutionary rehearsal function.
### VI. Sleep Disorders
Insomnia, the most common sleep disorder, involves difficulty falling or staying asleep or experiencing non-restorative sleep. It affects roughly 10-15% of adults chronically and can be caused by stress, anxiety, depression, poor sleep hygiene, or medical conditions. Cognitive-behavioral therapy for insomnia (CBT-I) is the preferred treatment over medication.
Sleep apnea involves repeated cessation of breathing during sleep. The most common form, obstructive sleep apnea, occurs when the airway collapses or becomes blocked, producing loud snoring, gasping, and daytime sleepiness. Risk factors include obesity, male sex, and older age. Treatment typically involves a CPAP machine, weight loss, or in some cases surgery.
Narcolepsy is characterized by sudden, uncontrollable sleep attacks during waking hours, sometimes accompanied by cataplexy — a sudden loss of muscle tone triggered by strong emotion. Narcolepsy has been linked to the loss of hypocretin (orexin)-producing neurons in the hypothalamus, and sufferers may also experience sleep paralysis and hypnagogic hallucinations.
Parasomnias include sleepwalking (somnambulism), which occurs during N3 sleep and is more common in children; night terrors, which are intense fear episodes during N3 sleep that are distinct from ordinary nightmares; and REM sleep behavior disorder, in which the normal REM atonia is lost and the person physically acts out dreams. REM sleep behavior disorder can be an early indicator of neurodegenerative diseases such as Parkinson's disease and Lewy body dementia. Restless legs syndrome (RLS) produces uncomfortable sensations in the legs accompanied by an urge to move, and symptoms are typically worse at rest.
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