Psych (9/30)

Human sleep varies widely, often averaging between 6-8 hours per night.
Not all organisms require the same amount of sleep, reflecting their metabolic and ecological needs.

Diurnal Animals (e.g., humans): Active during daylight; best suited for vision as the dominant sense.
Nocturnal Animals (e.g., bats, rodents): Active during nighttime; dominated by the sense of smell.
Crepuscular Animals (e.g., deer): Most active at dawn and dusk.

Humans typically sleep lying down.
Other species exhibit varied postures:
- Bats: Sleep upside down.
- Horses: Sleep standing up to avoid internal organ damage if they lie down.
- Some marine animals, e.g., dolphins, practice hemispheric sleep to maintain consciousness required for breathing.

Sleep is crucial for physical and cognitive health across species.
There is a strong relationship between amount of sleep and growth or environmental conditions, e.g., hibernation in animals to conserve energy during food scarcity.

Human sleep is composed of several distinct stages:
- Stage 1: Light sleep, transitional state, 5-10% of the night. Brain activity is still relatively high (4-7 Hz).
- Stage 2: More sleep spindles, represents about 50% of total sleep time. Associated with memory consolidation.
- Stage 3 (Slow Wave Sleep or NREM): Deep restorative sleep. Characterized by high amplitude, low frequency brain waves (0.5-4 Hz). Priority sleep state for physical recovery.
- REM Sleep: Associated with vivid dreaming. The brain exhibits high activity reminiscent of wakefulness, but the body is paralyzed to prevent acting out dreams. Occurs predominantly in the latter part of the sleep cycle.

Sleep cycles last approximately 90 minutes. Each night, multiple cycles include all sleep stages:
- Most slow wave sleep occurs in the first half of the night.
- REM periods increase in duration as the night progresses, correlating with deeper sleep needs earlier in the night.

Restoration Theory: Suggests sleep allows for physiological restoration and repair. Supported by patterns seen in young, growing individuals needing more sleep.
- Evidence: Infants and growing children require significantly more sleep due to rapid physical and neural development.
Adaptive Theory: Proposes that sleep patterns and needs evolved as adaptive strategies for survival within ecological contexts. This can explain differences across species.

Chronic sleep deprivation leads to physiological and cognitive deficits, impacting heart health and immune function.
Common experience: Extended wakefulness decreases cognitive performance and can lead to higher risks of accidents.

Humans are diurnal, suggesting a biological rhythm that aligns with daylight. Napping can affect the quality of consolidated sleep at night.
About 85% of mammals have polyphasic sleep patterns, sleeping multiple times throughout the day.

Dreaming occurs across all sleep stages, with significant dreams occurring mostly during REM sleep.
Dream content can be influenced by emotional and sensory experiences, often lacking logical coherence while being vivid and emotional.

Prioritizing sufficient sleep is critical for overall health, performance, and well-being. It is essential to establish a routine that supports full periods of sleep to optimize restorative functions and cognitive performance.
Monitoring sleep trends and adjusting sleep schedules can be beneficial to determine individual sleep needs.