Biological Rhythms And Sleep

Sleep-Wake Cycle

• Cycle persists despite isolation from light.
• Varies from person to person from 20 to 28 hours.
• Studies (cave study siffre) show cycles to be longer then 24 hours (supported by Aschoof and Wever, WW2 bunkers)

Core Body Temperature

•   Lowest around 4.30AM and highest around 6.00PM.
• Slight dip around lunch.

Hormones

• Cortisol lowest around midnight peaks around 6.00AM. Makes us alert when we wake up.
• Melotonin peaks at midnight, induces sleepyness.
• Growth hormone peaks at midnight.

Sleep-wake cycle

• research methodology; Although there was no natural light there was artificial light. Artificial light could affect them as well (Czeisler used dim lighting to down to 22 hours and up to 28 hours)
• Individual differences; Everyones cycle is different, can range all the way from 13 - 64 hours. Innately different for peak times.  Some people go to bed and wake up early, some go to bed and wake up late.

Core Body Temperature

• Has been linked to cognitive abilities, long term recall is best when body temperature is highest. (Folkard)
• When body temperature is lowered cognative performance was worse on some tasks (Giesbrecht)
• A study in field rather then a lab found that there wasn't a correlation (Hord and Thompson)
• Higher core tempurate may lead to increased physiological arousel and this leads to improved cognative performance (Wright)

Cycles within 24 hours

Sleep stages

• 5 stages of sleep.
• Each sleep cycle lasts, 60 minutes in infancy, 90 minutes during adolesemce.
• NREM SLEEP;
• Stages 1 & 2, relaxed state, easily woken, alpha and theta waves, heart rate slows, temperature drops.
• Stages 3 & 4, Delta waves, metabolilc rate slowest,  growth hormone produced.
• REM SLEEP;
• REM, called "paradoxial sleep" because nrain and eyes active but body paralysed.