Melinda • Melinda S. is a mother of two children, ages 13 and 11. They all go to bed at 4 am, and typically wake up around noon. This is not just on weekends: this is every day. Although some of her neighbors think she’s a bad mother, Melinda and her children are sufferers of delayed sleep phase syndrome, a disorder of the circadian rhythm in which a person has no trouble maintaining sleep, but cannot fall asleep and wake up at the same time as the rest of society (Dagan 2002). • Melinda has had a difficult time holding on to jobs that require her to be present early in the morning. Patients with these disorders of the circadian rhythm typically work to adapt their lives and careers around their own rhythms. She operates a business that she runs from home. Her children are home-schooled by Melinda through the afternoon and evening.
Why Sleep? • Energy is conserved during sleep: • Small animals sleep more than large ones, in correlation with their normal high metabolic rate. • Sleep helps animals avoid predators: • Animals sleep during the part of the day when they are most vulnerable. Sleep restores the body: • By replenishing metabolic requirements. Growth hormone is only released during SWS. • Sleep, especially REM, may actively improve processes that consolidate learned material
Daily Rhythms in Activity • Rhythms: behavioral, physiological, and biochemical. • Diurnal – active during the light • Nocturnal – active during the dark Circadian rhythms are about 24 hours. Circadian rhythms are generated by an endogenous (internal) clock.
Sleeping and Waking • Sleep is synchronized to external events, including light and dark. • Stimuli like lights, jobs, and alarm clocks entrain us to be awake or to sleep. • In the absence of cues, humans have a free-running period of ~25 hours that varies with age.
The Hypothalamus has an Endogenous Circadian Clock • Some biological rhythms are short: • bouts of activity, feeding, and hormone release. These ultradian rhythms occur more than once per day. • Other biological rhythms are long, such as reproductive cycles.
RetinohypothalamicPathway in Mammals In mammals, light information goes from the eye to the SCN via the retinohypothalamic pathway.
Effects of Lesions in the SCN Circadian rhythms are disrupted in SCN-lesioned animals
More than one endogenous clock • SCN lesions do not abolish infradian or ultradian rhythms in mammals • Mice with Clock/Clock mutation lose free-running circadian rhythms but not free-running ultradian rhythms. • An endogenous circannual clock, separate from the SCN, runs at ~365 days: • Anniversary effect
Thought experiment • Imagine you could have a painless, free, completely safe procedure that would eliminate the need to ever sleep. • Would you have it?
When the Endogenous Clock Goes Kaput Volunteer rat
Two classes of sleep • Slow-wave sleep (SWS) – four stages, characterized by slow-wave EEG activity • Rapid-eye-movement sleep (REM) • Beta (fast) EEG waves, rapid eye movements • Breathing and heart rate speed up • Muscles are relaxed ‘paradoxical sleep’
A Typical Night of Sleep in a Young Adult Cycles last 90–110 minutes, but cycles early in the night have more stage 3 and 4 SWS, and later cycles have more REM sleep
Human Sleep Exhibits Different Stages • Vivid dreams occur in REM sleep, characterized by: • Visual imagery • Sense that the dreamer is “there” • Nightmares are frightening dreams that awaken the sleeper from REM sleep. • Night terrors are sudden arousals from stage 3 or 4 SWS, marked by fear and autonomic activity.
Marine mammals do not show REM sleep, perhaps because relaxed muscles are incompatible with 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.
As people age, total time asleep declines, and number of awakenings increases. The most dramatic decline is the loss of time spent in stages 3 and 4. Infant sleep: Shorter sleep cycles More REM sleep
At Least Four Interacting Neural Systems Underlie Sleep • forebrain system – displays SWS • brainstem system – activates the forebrain • pontine system – triggers REM sleep; paralyzes body • hypothalamic system – affects all above Sleep is an active state
Effects of sleep deprivation – partial or total: • Increased irritability • Difficulty in concentrating • Episodes of disorientation • Effects vary with age
Is insomnia fatal? Do We Need Sleep? 20 year old student, Jonathan Daley, John Moores University, Liverpool, broke the world record by staying awake 502 hours (21 days). Award for Serious Cramming.
Narcolepsy sufferers: • Frequent sleep attacks and excessive daytime sleepiness • Do not go through SWS before REM sleep • May show cataplexy – sudden loss of muscle tone, collapse
Narcoleptic dogs have a mutant gene for a hypocretin receptor. • Hypocretin normally prevents the transition from wakefulness directly into REM sleep. • These neurons are attacked by T cells.
Sleep disorders • Sleep paralysis - the brief inability to move just before falling asleep, or just after waking up; caused by the pontine center continuing to signal for muscle relaxation, even when awake. • Night terrors and sleep enuresis (bed-wetting) are associated with SWS
Sleep disorders • Somnambulism (sleepwalking) occurs during stages 3 and 4 SWS, and may persist into adulthood.
Sleep Disorders Can Be Serious, Even Life-Threatening • Sleep apnea: • Breathing may stop – blood oxygen drops rapidly. • Chest/diaphragm muscles relax too much or pacemaker respiratory neurons in brain stem do not signal properly. • Sleep apnea often accompanied by snoring. • Each episode ofsleep apnea arouses the person to restore breathing, but results in daytime sleepiness.
Diagnosis Of OSA • Overnight polysomnogram (PSG)
Treatments include CPAP (continuous positive airway pressure) machine, to prevent collapse of the airways. • Untreatedsleep apnea can lead to heart failure.
Kleine-Levin hibernation syndrome • Symptoms are cyclical: • excessive sleep (hypersomnolence), (up to 20 hours a day) • excessive food intake (compulsive hyperphagia) • behavior changes such as uninhibited sexual drive • primarily affects adolescent males • When awake, individuals are irritable, lethargic, and apathetic. They may also be confused and hallucinate.
REM sleep behavior disorder, in which the muscle atonia that usually accompanies REM stage is absent. Sleepers therefore will act out their dreams, which usually results in injury to themselves or others. Ninety percent of patients with this disorder are male, and they will sometimes try to deal with the problem by tying themselves directly to the bed and/or constructing fortresses of pillows.
Back to Sleep 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 aids • Sleeping pills are not perfect • – most bind to GABA receptors throughout the brain. • Continued use of sleeping pills: • Makes them ineffective (receptor downregulation) • Change sleep patterns that persist even when not taking the drug • Can lead to drowsiness and memory gaps
Good sleep practices • * Fix a bedtime and an awakening time. The body "gets used" to falling asleep at a certain time, but only if this is relatively fixed. • * Avoid napping during the day. • * Avoid alcohol and caffeine 4-6 hours before bedtime. • *Exercise regularly, but not right before bed. Regular exercise, particularly in the afternoon, can help deepen sleep. • * Try a light snack before bed. Warm milk and foods high in the amino acid tryptophan, such as bananas, may help you to sleep. • * Establish a pre-sleep ritual such as a warm bath or a few minutes of reading. If you don't fall asleep within 15-30 minutes, get up, go into another room, and read until sleepy. • * Reserve the bed for sleep and sex. Don't use the bed as an office, workroom or recreation room.