Consciousness and sleep | 6B: Making sense of the environment | Psych/soc

Consciousness

Consciousness is our awareness of both internal sensations and the external world. This includes:

Internal awareness: Recognizing bodily signals like pain, hunger, thirst, and sleepiness, as well as our own thoughts and emotions.
External awareness: Perceiving environmental stimuli such as sunlight, warmth, and the sound of a friend’s voice.

Consciousness exists on a continuum—from full alertness during wakefulness to the deep inactivity of sleep. While being awake involves high sensory awareness, active thought, and behavior, sleep is a state of reduced physical activity and sensory perception. Additional states include daydreaming, intoxication, and medically induced unconsciousness.

States of consciousness

Alertness
The ability to remain attentive and focused on the surrounding environment.

Influences: Regulated by the reticular activating system (RAS) in the brainstem and synchronized with our natural 24-hour circadian rhythm.
Disruptions: Can be affected by drugs, toxins, head injuries, or conditions like ADHD, depression, and chronic fatigue.

Sleep

A distinct state characterized by diminished sensory awareness and low physical activity, different from mere rest during wakefulness.

Measurement: Polysomnography monitors sleep by recording eye movements (EOG), brain electrical activity (EEG), and muscle activity (EMG).

Brain waves and sleep stages

Awake: Dominated by beta waves—high frequency ( $13-30 Hz$ ) and low amplitude.
NREM sleep: Divided into three stages:
- Stage 1: A transitional phase with slowing brain waves (alpha waves transitioning to theta waves), reduced heart rate, respiration, muscle tension, and body temperature. Easily disrupted.

Stage 2: Characterized by continued theta wave activity interspersed with sleep spindles—brief bursts of faster brain waves that may support learning and memory.
- Stage 3 (deep sleep): Marked by low-frequency, high-amplitude delta waves (less than $3 Hz$ ), significant slowing of physiological processes, and a deeper, harder-to-disrupt sleep.
REM sleep: Distinguished by rapid eye movements, brain wave patterns similar to wakefulness, and a temporary paralysis of most voluntary muscles, allowing for vivid dreaming.
REM rebound: Occurs when deprived of REM sleep, leading to longer periods of REM when sleep is allowed.

Hypnogram showing sleep stages through a sleep cycle

Circadian rhythms and sleep regulation

Circadian rhythm: A roughly 24-hour cycle governing sleep-wake patterns, influenced by natural light-dark cycles.
Suprachiasmatic nucleus (SCN): Located in the hypothalamus, this internal clock receives light input from the retina to synchronize our circadian rhythm.
Melatonin: A hormone from the pineal gland that promotes sleep, released in response to darkness and suppressed by light.
Chronotypes: Individual differences in sleep patterns, such as being a morning person or a night owl.

Suprachiasmatic nucleus and circadian rhythm brain clock

Sleep cycles and changes throughout the night

A complete sleep cycle, lasting about 90 minutes, progresses through NREM stages (1 to 3) before transitioning into REM sleep. As the night advances, the duration of deep sleep (stage 3) decreases, while REM periods lengthen.

Theories on the functions of sleep

Sleep serves multiple purposes:

Adaptation: Conserving energy and avoiding predators during the night.
Restoration: Facilitating bodily repair and brain recovery.
Growth: Promoting the release of growth hormones, particularly during developmental stages.
Memory processing: Aiding in the consolidation of daily experiences into long-term memories.

Dreaming

Occurrence: Dreams mainly occur during REM sleep.

Dreaming theories:

Freud’s model: Differentiates between the literal content (manifest) and the hidden meaning (latent) of dreams.

Jung’s concept: Introduces the idea of a collective unconscious with universal symbols.

Activation-synthesis theory (Hobson): Proposes that dreams result from the brain’s effort to interpret random neural activity during REM sleep.

Sleep-wake disorders

Parasomnias: Abnormal behaviors during sleep, such as sleepwalking, restless leg syndrome, and night terrors, typically occurring during slow-wave (deep) sleep.

Dyssomnias: Disruptions in sleep quantity, quality, or timing, including:

Sleep apnea: Episodes where breathing stops temporarily, leading to fragmented sleep and daytime fatigue.
Narcolepsy: Sudden, uncontrollable sleep episodes, sometimes accompanied by muscle weakness (cataplexy).
Insomnia: Persistent difficulty falling or staying asleep, often linked to stress and sometimes treated with medication.