Biological Rhythms and Sleep Study Notes

Circadian Rhythms and Sleep
- Explore how we measure sleep using EEG (Electroencephalogram)
- Different stages of sleep:
- Definition and significance of each stage
- What happens during these stages
- Sleep deprivation studies: insights gained from research
- Theories explaining the need for sleep

Suprachiasmatic Nucleus (SCN) as the biological clock:
- Controls various biological rhythms
- Acts as a master oscillator regulating other rhythms
- Removal (lesioning) of SCN disrupts all other physiological cycles

Melatonin Hormone:
- Produced by the pineal gland, deep in the brain
- Regulated by SCN input
- Influences multiple tissues, coordinating circadian responses
- Commonly used as a sleep aid and for treating jet lag
- Functions as a secondary zeitgeber for blind individuals to regulate their rhythms
- Peak Levels: Highest at night, playing a crucial role in sleep induction

Mechanism of SCN:
- Interplay of various genes that regulate the clock (endogenous rhythm of ~24 hours)
- Light input through the Retinohypothalamic Tract (RHT) resets daily rhythms
- Specific proteins (Per/Cry and Cl/Cy) interrelate, contributing to timekeeping

Zeitgeber Definition: Regular stimuli that reinforce biological cycles (e.g., light at dawn)
- Disruptions in rhythms lead to sleep issues:
- Shift Work: Adapting sleep-wake cycle without changing zeitgebers
- Jet Lag: Cycles failing to sync with new time zone leads to sleep urge misalignment
- The impact of different time zones on sleep patterns and duration

EEG (Electroencephalogram):
- Reveals brainwaves, crucial for sleep stage determination
- Established guidelines in 1968
EOG (Electrooculogram):
- Tracks eye movements during REM sleep
EMG (Electromyogram):
- Detects loss of muscle activity during sleep stages

Waveform Definitions:
- Alpha (9-14 Hz): Relaxation and calm
- Beta (15-30 Hz): Awake and alert
- Theta (4-8 Hz): Deep relaxation and meditation
- Delta (1-3 Hz): Deep, dreamless sleep

Stage 1: Similar to awake state, marked by theta waves (4-7 Hz)
Stage 2: Features K complexes and sleep spindles (linked to memory)
Stages 3/4: Known as Slow Wave Sleep (SWS) with large delta waves
REM Sleep:
- Characterized by desynchronized EEG similar to awake state
- Exhibits rapid eye movement and dreams

SWS Features:
- Significant decreases in cerebral metabolism (75%)
- Dominance of the parasympathetic system
- Increased growth hormone release; potential 'brainwashing' effect for waste removal
REM Features:
- Dreaming state with fluctuating vital signs
- Increased cerebral blood flow, can be easily awakened
- PGO wave activity: electrical signals linked to REM cycle

Freudian Dream Theory: Reconciling repressed wishes; differentiate between manifest (experienced) and latent (meaning) content with limited evidence.
Activation-Synthesis Theory: Dreams arise from the cortex trying to make sense of random neural activity.
Neurocognitive Theory: Dreams are narrative sequences similar to waking consciousness but without external stimuli.

Sleep Deprivation Research: Studies on both complete vs partial sleep loss in animals and humans.
Effects observed include cognitive deficits, such as impaired attention, decision-making even after recovery.
Both REM and SWS are critical for memory consolidation.
Energy Conservation and Restoration: Sleep’s role in repairing biological processes.
- Lack of sleep worsens performance dramatically for repetitive tasks over others.
Adaptive Theory: Sleep aids survival and reduces vulnerability to predation; sleep patterns vary across species.

Examples include fatal familial insomnia in humans and sleep adaptations in cetaceans, showing variation in sleep necessity.