Evolution of Sleep Wake Cycles

•Most living organisms, exhibit a circadian rest-activity rhythm

•Sleep-Wake may have evolved from rest-activity rhythm

•Sleep evolved early in the development of multicellular animals

•Sleep is beneficial to fruit flies, orcas, humming birds, and humans

•Animals have evolved sleep patterns as part of adapting to their ecological niche

•So there is variation in sleep patterns across groups of animals

Amounts of Different Sleep States in Various Mammals

Sleep in Marine Mammals

Function of REM Stage of Sleep

•Uncertainty about the purposes of REM sleep and dreaming

•Subjects compensate for the lack of REM sleep by having more of it after deprivation

•Deprivation of REM sleep in humans for as much as two weeks has little or no obvious effect on behavior

•Patients taking certain antidepressants (MAO inhibitors) have little or no REM sleep, yet show no obvious ill effects

Function of REM Stage of Sleep

•REM sleep is involved in the transfer of memories between the hippocampus and neocortex.

•Reinforces behaviors not commonly encountered during the awake state (aggression, fearful situations)

•Act as an “unlearning” mechanism, whereby certain modes of neural activity are erased by random activation of cortical connections

Development of Sleep – Wake Cycle•The sleep-wake cycle take time to develop, resulting in the irregular sleep schedules of newborns.

•The rhythms begin to develop at about six weeks, and by three to six months most infants have a regular sleep-wake cycle

•Babies spend 50 percent of their time in REM and the sleep cycle is about 50 minutes.

•Sleep is especially important for children as it directly impacts mental and physical development.

The Trouble with Babies

Human Sleep Patterns Change with Age

The Typical Pattern of Sleep in an “Unhealthy” Elderly Person

Changes in Sleep Patterns with Aging

•Total amount of sleep decreases, less stage 3-4, more awakenings and insomnia is a common complaint

•Many sleep problems are not a natural part of sleep in the elderly

•Sleep disruption from medical conditions such as apnea, enlarged prostate or medications they are taking

•Sleep dyssynchrony from lifestyle changes such as decreased activity and napping

•Prevalence of sleep problems is very low in healthy older adults

• YOUR GUIDE TO Healthy Sleep NIH Publication No. 11-5271 Originally printed November 2005 Revised August 2011 •http://www.nhlbi.nih.gov/health/public/sleep/healthy_sleep.pdf

What Are the Biological Functions of Sleep?

• What Are the Biological Functions of Sleep? – Energy conservation– Niche adaptation– Body restoration– Memory consolidation

• However a few people sleep very little– Whatever the function of sleep– these people fill it with a brief nap– yet are normal and healthy

Memory Consolidation in Slow- Wave Sleep (Part 1)

At Least Four Interacting Neural Systems Underlie Sleep

Sleep is an active state mediated by:

1. A forebrain system–displays SWS

2. A brainstem system–activates the forebrain

3. A pontine system–triggers REM sleep

4. A hypothalamic system–affects the other three

Brain Mechanisms Underlying Sleep

Neurotransmitter Systems Affected by General Anesthetics

Classification of Sleep Disorders

Sleep Recovery after 11 Days Awake

Sleep Demand

• Sleep demand is an automatic onset of drowsiness

• Rebound after deprivation– Amount of SWS– Amount of REM– Change in sleep stage pattern

• Functions of Sleep– Rest and Recovery– Memory Consolidation– Energy Efficiency

Sleep Deprivation Effects

• Numerous ill effects – Deficient immune system

• Greater likelihood of illness

• Slower recovery from infection

• Fatal with long-term disruption

– Increased Risk of Accidents• Reduced motor coordination

• Slow reaction time

– Makes you stupid• Impaired long-term memory

• Slower decision making

• Impaired problem solving

Shift in Dark-Light Cycle

• Changes in schedule require adjustment– Work schedule shift change– Jet Lag– Irregular sleep patterns

• Amount of adjustment depends on:– Duration of shift– Direction of shift– Physiological system being measured

• Sleep-wake cycle

• Body temperature

• Hormones

Duration of Shift• Most studies used three or more hours

– Jet lag from flying easterly across three time zones (phase advance)

– Phase shift in a lab of three or more hours• Recent data from Daylight Saving Time

– One hour shift• Phase Advance in the spring• Phase Delay in the fall

– Three possible effects• One hour of sleep deprivation in spring• Disrupt sleep-wake cycle• Changes in social activities

– Fooling with the Zietgieber• Sun rises and sets as usual• Work schedule does not change• Activity pattern is not in sync with biorhythms

Irregular Sleep Patterns

• Similar to Jet Lag but without changing time zones• Time of sleep onset and waking varies from day to day

– Usually delayed sleep onset– Combined with delayed waking

• Exposure to light resets SCN– Reset at different times across several days– SCN regulated biorhythms can not adjust– Similar to chronic jet lag

• Sleep deprivation– Delayed sleep onset combined with regular waking

time – Working all night without sleep

Delayed Sleep Phase Syndrome (DSPS)

• Symptoms– Complaint of insomnia or excessive sleepiness

• inability to fall asleep at the desired time • inability to wake up at the desired time

– Depression may be present – Persistent for 3 months

• Onset– Usually during adolescence– After a period of late night studying or partying

• Treatment– Improve sleep hygiene habits – Bright Light Therapy – Chronotherapy