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 REM sleep evolved in some vertebrates: Nearly all mammals display both REM and SWS. Birds also display both REM and SWS sleep. A sleep cycle is a period of SWS followed by one of REM sleep. For humans, the sleep cycle is 90–110 minutes. Most vertebrates show: A circadian distribution of activity A prolonged phase of inactivity Raised thresholds to external stimuli Characteristic posture

Sleep in Marine Mammals Dolphins do not show REM sleep, perhaps because relaxed muscles are incompatible with the need to come to the surface to breathe. In dolphins and birds, only one brain hemisphere enters SWS at a time; the other remains awake. Unilateral SWS probably allows dolphins and birds to continue functioning but rest half the brain while moving.

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 Mammals sleep more during infancy than in adulthood. Infant sleep is characterized by: Shorter sleep cycles More REM sleep—50%, which may provide essential stimulation to the developing nervous system

Human Sleep Patterns Change with Age

The Typical Pattern of Sleep in an “Unhealthy” Elderly Person As people age, total time asleep declines, and the number of awakenings increases. The most dramatic decline is the loss of time spent in stage 3: At age 60, only half as much time is spent in stage 3 as at age 20; by age 90, stage 3 has disappeared.

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? 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) Explanations for memory consolidation and learning vary from passive to active: Sleep during the interval between learning and recall may reduce interfering stimuli. Memory typically decays, and sleep may slow this down. Alternatively, sleep, especially REM, may actively contribute through processes that consolidate the learned material. Growing evidence suggests that patterns of neuronal activity seen while a task is being learned during wakefulness are re-created during subsequent SWS. A cue has been used to ‘reactivate’ learning during SWS.

At Least Four Interacting Neural Systems Underlie Sleep Sleep is an active state mediated by: A forebrain system–displays SWS A brainstem system–activates the forebrain A pontine system–triggers REM sleep A hypothalamic system–affects the other three

Brain Mechanisms Underlying Sleep The reticular formation is able to activate the cortex. Electrical stimulation of this area will wake up sleeping animals while lesions of this area promote sleep. The forebrain and reticular formation seem to guide the brain between SWS and wakefulness. An area of the pons, near the locus coeruleus, is responsible for REM sleep. Some neurons in this region are only active during REM sleep. They inhibit motoneurons to keep them from firing, disabling the motor system during REM sleep. The study of narcolepsy revealed the hypothalamic sleep center. Narcolepsy sufferers: Have frequent sleep attacks and excessive daytime sleepiness Do not go through SWS before REM sleep May show cataplexy–a sudden loss of muscle tone, leading to collapse Narcoleptic dogs have a mutant gene for a hypocretin receptor. Hypocretin normally prevents the transition from wakefulness directly into REM sleep. Interfering with hypocretin signaling leads to narcolepsy. Hypocretin neurons in the hypothalamus project to other sleep system centers: the basal forebrain, the reticular formation, and the locus coeruleus. Axons also go to the tuberomamillary nucleus, whose inhibition induces SWS. The hypothalamus seems to contain a hypocretin sleep that controls wakefulness, SWS sleep, or REM sleep. Sleep paralysis is the brief inability to move just before falling asleep, or just after waking up. It may be caused by the pontine center continuing to signal for muscle relaxation, even when awake.

Neurotransmitter Systems Affected by General Anesthetics General anesthetics produce slow waves in EEG that resemble SWS. Almost all general anesthetics are agonists of GABAA receptors–this suggests some brain system uses GABA to promote SWS. Most sleeping pills bind to GABA receptors throughout the brain. Continued use of sleeping pills: Makes them ineffective Produces marked changes in sleep patterns that persist even when not taking the drug Can lead to drowsiness and memory gaps

Classification of Sleep Disorders Sleep disorders in children: Night terrors and sleep enuresis (bed-wetting) are associated with SWS. Somnambulism (sleepwalking) occurs during stages 3 and 4 SWS, and may persist into adulthood. REM behavior disorder (RBD) is characterized by organized behavior, from an asleep person. It usually begins after age 50 and may be followed by beginning symptoms of Parkinson’s disease. This suggests damage in the brain motor systems. Sleep state misperception occurs when people report insomnia even when they were asleep. Sleep-onset insomnia is a difficulty in falling asleep, and can be caused by situational factors, such as shift work or jet lag. Sleep-maintenance insomnia is a difficulty in staying asleep and may be caused by drugs or neurological factors. In sleep apnea, breathing may stop or slow down–blood oxygen drops rapidly. Muscles in the chest and diaphragm may relax too much or pacemaker respiratory neurons in the brain stem may not signal properly. Sleep apnea may be accompanied by snoring. Each episode of sleep apnea arouses the person to restore breathing, but may result in daytime sleepiness. Treatments include a removable tube in the throat or a CPAP (continuous positive airway pressure) machine, to prevent collapse of the airways. Untreated sleep apnea can lead to cardiovascular disorders. Sudden infant death syndrome (SIDS) is sleep apnea resulting from immature respiratory pacemaker systems or arousal mechanisms. Putting babies to sleep on their backs can prevent suffocation due to apnea.

Sleep Recovery after 11 Days Awake Effects of sleep deprivation—the partial or total prevention of sleep: Increased irritability Difficulty in concentrating Episodes of disorientation Effects can vary with age and other factors. Total sleep deprivation compromises the immune system and leads to death. The disease fatal familial insomnia is inherited. In midlife, people stop sleeping and die 7–24 months after onset of the insomnia. Autopsy shows degeneration in the brain. Sleep recovery is the process of sleeping more than normally, after a period of deprivation. Night 1—stage 3 sleep is increased, but stage 2 is decreased. Night 2—most recovery of REM sleep, which is more intense than normal with more rapid eye movements

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