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10/20/2016 Sleep and Biological Rhythms Theories of Sleep Function • Restorative Hypothesis • Sleep is a time to restore and repair the nervous system. • Sleep time might vary depending on how much restoration was necessary (e.g. after an active day vs a quiet day) • Adaptive Hypothesis • Sleep has survival value beyond its restorative functions. • Sleep time of a species depends on safety & food acquisition issues. • E.g., predators (lions) & species that can hide (bats) sleep a lot. • Vulnerable animals (cattle) & those that need to spend hours feeding (elephants) sleep very little. • Need for safety & conservation of energy are more constant needs. 10/20/2016 Garrett: Brain & Behavior 4e 2 Sleep and Dreaming Figure 15.1: Time Spent in Daily Sleep for Different Animals • Built-in biological rhythms could encourage conservation of energy & safety at the times when food-seeking is inefficient and/or dangerous • Circadian rhythms timed to the day/night cycle would do so. Garrett: Brain SOURCE: Based on data from “Animal Sleep: A Review of Sleep Duration Across Phylogeny, by S. & S. Behavior Campbell4e and I. Tobler, 1984, Neuroscience and Biobehavioral Reviews, 8, 269– 3 300. 10/20/2016 Garrett: Brain & Behavior 4e 4 2 Day Circadian Examples Rhythms of Waking and Sleep • All animals produce endogenous circadian rhythms, internal mechanisms that operate on an approximately 24 hour cycle to regulate: • • • • Wakefulness and sleep Body temperature Secretion of hormones Many other biological processes Peaks ~ 6 hr before bedtime Lowest~2 hrs into sleep • Endogenous – generated from within. Rhythms continue even in the absence of all environmental cues about the day/night cycle. 1 10/20/2016 Key Circadian Clock: Suprachiasmatic Nucleus of Hypothalamus (SCN) Rhythms • Some animals generate: • Circannual rhythms -operate on an annual or yearly cycle (e.g. migration, hibernation) • Circalunar rhythms – e.g. menstrual cycle • Shorter rhythms – e.g. ~90 minute cycle within sleep • Light resets the SCN via direct connection from the retina: retinohypothalamic path. • Comes from a special group of ganglion cells that have their own photopigment called melanopsin. • These cells respond directly to light and do not require any input from the rods or cones. • Light resets the SCN via direct connection from the retina: retinohypothalamic path. • Comes from a special group of ganglion cells that have their own photopigment called melanopsin. • These cells respond directly to light and do not require any input from the rods or cones. • In the absence of environmental cues, our circadian rhythms are “free-running” on a slightly more than 24 hr cycle (e.g. 24.5 hrs) • Normally environmental cues “re-set” the clock & keep it to a 24 hr schedule. These cues are called “zeitgebers” • Light is the primary one. • Exercise, noise, meals, and temperature are others zeitgebers. 10/20/2016 Garrett: Brain & Behavior 4e 12 2 10/20/2016 “Free-Running Rhythm” Sleep hours of someone without environmental indicators of time (very similar to Fig. 9.1 of a squirrel’s rhythms without outside cues) On a lighter note: • http://www.youtube.com/watch?v=KnJkMfmea28&feature=related After 2 weeks w/o lighting cues his bedtime is ~10-11 hrs out of synch with the real world Rhythms Depend on Their Clock Activity cycles (black) of rats before (top) and after (bottom) SCN lesions • SCN lesions disrupt activity, sleep, eating, & hormone rhythms. • SCN transplants can change an animal’s natural biorhythm to that of donor. • SCN very sensitive, very adaptive – this allows “resetting” of our biological clock with the seasons, changes in time zones, etc. • Retinal blindness can disturb resetting if it affects these ganglion cells • Some blind individuals have “free-running rhythms” for this reason. • But under normal conditions our internal clock itself is very resistant to disruption. • The SCN regulates the pineal gland, an endocrine gland located posterior to the thalamus. • The pineal gland secretes melatonin, a hormone that increases sleepiness. 3 10/20/2016 Circadian Rhythm Problems • Jet lag: mismatch between circadian rhythms & outside world due to crossing time zones. • Sleepiness & impaired functioning during the day and sleeplessness at night until clock re-synchronizes with new environment • Traveling west = “phase-delay”, traveling east= “phaseadvance”. Phase delays are easier for your clock to adjust to. • Shift-work sleep disorder, similarly, is related to trying to work when your circadian clock is telling you to sleep and trying to sleep when your SCN is telling you it is time to be awake. Desynchronization of work cycle and circadian cycle correlated with accidents • Knowing how to best handle jetlag and shiftwork is of importance to a huge number of businesses & international interactions. Sleep Disorders Figure 15.14: Effects of Disrupted Circadian Rhythm on Sleep. • Insomnia may have many causes, but sometimes is linked to abnormal circadian rhythms • Circadian phase delay- body temp decrease & sleepiness delayed – have trouble getting to sleep • Circadian phase advancebody temp drop & rise occurs early. Get sleepy early, wake up really early. Garrett: Brain & Behavior 4e 22 Polysomnogram Phase advanced Owls vs Larks Phase-delayed (“multiple sleep recordings”) • EEG (electroencephalogram) • EOG (electrooculogram) • EMG (electromyogram) • Sometimes additional measures • Expression of the related genes may change over the lifespan. The owl/lark difference is seen mostly in adolescence/early adulthood. 4 10/20/2016 EEG A Typical Night’s Sleep Beta waves or LVFdesynchronized More rhythmical 10-12 cps Longest dreams The deeper the sleep, the more neurons fire in rhythm with each other Longest NREM ~90 minute cycles within sleep Looks like beta waves of wakefulness Figure 15.6: Time Spent in Various Sleep Stages • The sleeper returns through the stages in reverse order Non-REM Sleep (Stages 1-4) (80% of night) • gradual decrease in movements, breathing, heart rate • change in brain activity from little (low voltage) fast brain waves to big (high voltage) slow, rhythmical brain waves (“delta waves”) • hard to wake up • sleep-thinking more common than dreaming • Only rarely (10% of the time) will you report a dream • Stage 1 is replaced by rapid eye movement (REM) sleep • If you sleep longer you’d have more cycles/more dreams Garrett: Brain & Behavior 4e REM Sleep (20% of night) • very active LVF irregular brain waves similar to waking • rapid jerky eye movements • total loss of tone in most muscles • breathing, heart rate unpredictable • 80-90% chance of vivid dream report • erection; vaginal lubrication • Most often missing REM REM rebound 27 Reticular Activating System Basal forebrain ACh neurons (PPT/LDT nuclei) Sends excitatory ACh, NE, and glutamate messages to all of forebrain. Other “stay awake” transmitters in parts of the hypothalamus are orexin and histamine (that’s why some ANTIhistamines make you sleepy) 5 10/20/2016 Sleep and Dreaming Figure 15.9: Brain Mechanisms of Sleep. • Brain Structures of Sleep and Waking • During waking, the reticular formation arouses entire cortex. Sleep does not work this way. • GABA & adenosine promote sleep, but in a more “region by region” fashion. So there are situations where part of the brain is asleep but not the entire brain. • Drugs that increase effect of GABA (tranquilizers, sleeping pills, alcohol) can facilitate sleep. Drugs that block adenosine (caffeine) can prevent sleep. • Sleep Controls • Adenosine accumulates in basal forebrain area & hyp. preoptic area during wakefulness, ultimately induces drowsiness, suppressing activity in wakefulness areas like RF & locus coeruleus. • Preoptic area and pons particularly important for sleep regulation Garrett: Brain & Behavior 4e NREM Sleep “Disorders” • Tend to run in families • Very common in kids. Most outgrow them- only a few adults continue to experience some episodes of NREM disorders. • Sleep-walking (17% of kids (peaking at 8-12 yrs), 4% of adults) • Can be triggered by stress, sleep deprivation, alcohol or Ambien type drugs • Individual may engage in quite complex behaviors while sleepwalking • Part of brain asleep, part of brain awake • Night terrors (3% of kids, mostly < 6 yrs) • Bed-wetting REM Behavior Disorder • REM behavior disorder - failure of the usual muscle paralysis mechanism of REM so the person can move during dreaming • Unlike narcolepsy, REM behavior disorder usually occurs in older individuals • May be associated brain damage/neurological disease like Parkinson’s disease • May be triggered by drug use in some • Treatment – medications that decrease REM 31 REM Sleep Disorders • Much more rare than NREM problems • Narcolepsy - REM sleep “attacks” with cataplexy (sudden loss of muscle tone), muscle paralysis, & hypnagogic hallucinations. Often triggered by emotion. May have mutation of a gene which in turn reduces orexin (a “stayawake” transmitter) • Animal Model of narcolepsy allows research Several meds can decrease sleep attacks of narcolepsy: -stimulants like Ritalin or amphetamine or the somewhat safer Provigil (modafinil) - or by deepening sleep at night with Xyrem Other Sleep Problems • Insomnia (over 60 varieties/causes) • Treatments: • • • • Good sleep “hygiene” or rituals OTC sleeping pills contain antihistamine (diphenhydramine) or the dietary supplement melatonin Prescription • Benzodiazepines- (Xanax, Dalmane, Halcion) • Non-benzodiazepines (Ambien, Lunesta, Sonata,) • Sleep Apnea • CPAP • Mouthpiece that adjusts jaw position • Tonsillectomy in kids 6