Sleep and Circadian Rhythms

Importance of Sleep
- Refreshing sleep experience without an alarm clock
Statistics on Sleep
- Two-thirds of adults do not meet the recommended sleep duration
- Recommended sleep duration is seven to nine hours per night
Health Implications of Sleep Deprivation
- Routinely sleeping less than six to seven hours can:
- Impair the immune system
- Double the risk for various diseases (cancer, heart disease, diabetes)
- Increase risk of mental health issues (depression, anxiety disorders)
- Lead to dementia later in life
- Severe sleep deprivation can be fatal.

Definition
- A pattern of bodily activities that lasts about 24 hours, including physical, behavioral, and biological changes.
Control of Circadian Rhythms
- Two main influences:
- Environmental factors (e.g., sunlight)
- Internal clock (endogenous oscillator)
- Internal clock operates independently in the absence of external cues.
- Example: An individual in a dark room shows changes in subjective day/night perception.
Functions of Circadian Rhythms
- Serves as the pacemaker for daily activity.
- Regulates:
- Arousal levels
- Metabolism
- Hormonal activity
- Physical states coincide with time of day (e.g., highest alertness, fastest reaction times, hormonal releases).

Factors that can disrupt:
- Jet lag
- Shift work
- Certain neuropsychiatric disorders

Function of the SCN
- Composed of core and shell parts.
- Special retinal ganglion cells (M1 RGCs) with melanopsin send signals to SCN when activated by light.
- SCN controls sleep via:
- Targeting the pineal gland for melatonin secretion.

Evolutionary or Conservation Theory
- Sleep may conserve energy and provide protection.
Restorative Explanations
- Sleep replenishes neurotransmitters and retunes synaptic receptor sensitivity.
- Enhances memory consolidation, noted via impaired tasks in sleep-deprived subjects.

Definition and Nature
- Part of circadian cycle.
- An altered state of consciousness characterized by physiological stages measured via EEG.
EEG Patterns
- Four major types by frequency:
- Beta: 13 to 20 Hz
- Alpha: 8 to 12 Hz
- Theta: 4 to 7 Hz
- Delta: 1 to 4 Hz
- Sleep spindles: 12 to 14 Hz
Sleep Stages Defined by EEG
- Stage 1: Transition from waking to alpha waves.
- Stage 2: Transition from alpha to theta.
- Stage 3: Mix of theta and delta waves.
- Stage 4: Dominantly delta waves (slow-wave sleep).
- REM sleep: Known as paradoxical sleep, lasting 10 to 20 minutes with rapid eye movements.

Dream Characteristics:
- Associated with periods of cortical activity during sleep involving images, ideas, and emotions.
- More likely to be remembered if awakened during REM sleep.
- Dreams exhibit a bizarre quality distinct from waking thoughts.
Theories on Dreaming:
- Freudian Perspective: Dreams reflect the unconscious mind's deepest desires and anxieties, often tied to repressed memories.
- Current Theories: Dreams relate to memory formation processes, influenced by the quieting of the prefrontal cortex during REM sleep.

Definition: A category of sleep disorders characterized by issues directly affecting the sleep process.
Examples include:
- Hypersomnia: Sleeping excessively or at inappropriate times.
- Insomnia: Divided into sleep onset (trouble falling asleep) and sleep maintenance (trouble staying asleep).
- Narcolepsy: Excessive daytime sleepiness and brief involuntary sleep episodes, often triggered by strong emotions.
- Sleep apnea: Includes obstructive sleep apnea (airway blockage) and central sleep apnea (issues in the brain stem).