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Chapter 11

PSYB64 chapter 11

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Pare, Dwayne

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PSYB64 – Chapter 11: Sleep and Waking Circadian Rhythms  The interplay between sleep and waking cycles follows circadian (daily) rhythms  To maintain these biological rhythms, internal biological clocks interact with stimuli called zeitgebers o Light is the most important zeitgeber for human beings o In the absence of natural light, human free running circadian rhythms last about 24.2 hours to 24.9 hours o Exposure to sunlight helps reset , or entrain, the internal biological clock to the 24-hour cycle of the earth’s rotation  Totally blind people and sailors on submarines experience free-running cycles that are longer than 24 hours, often resulting in severe sleep disruptions  Other zeitgebers include physical activity, feeding, body temperature, and sleep-related hormones Variations in Sleep Patterns  People who are most alert and productive in the morning have been referred to as “larks” whereas night people have been referred to as “night owls”  Nearly everyone acts like an owl during adolescence  Melatonin (one of the neurochemicals involved in sleep regulation) drops dramatically at the onset of puberty, contributing to age-related changes in sleep habits  Following adolescence, many temporary owls will revert to their previous state, possibly due to the maturation of neural systems that regulate sleep  Shifting from a 7:15am start time to an 8:40am start time improved attendance and student grades at Minnesota high schools Shift Work, Jet Lag, and Daylight Saving Time  Between 40-80% workers on the 11:00pm to 7:30am night shift experience disturbed sleep and a cluster of symptoms called shift maladaptation syndrome which can lead to frequent health, personality, mood, and interpersonal problems  Accident rates in the 3:00pm to 11:30pm shift are higher than in the traditional day shift and higher still during the 11:00pm to 7:30am  Night shift workers are more likely than other workers to develop breast cancer  Hospital workers such as nurses are more likely to make significant errors during the evening or night shifts than during day shifts  Conflicts between internal clocks and external zeitgebers also result in the unsettling experience of jet lag  Airline flight attendants who crossed the time zones at least once a week for 4 years or more had reduced reaction times and made 9% more mistakes on memory tasks than local crews who didn’t cross time zones  Because the human free running cycle is more than 24 hours long, people adjust more readily when travel or changes in shift work require us to stay up later and sleep later o It is easier to adjust to a phase delay of our cycle (setting the clock to a later point) than to a phase-advance (setting the clock to an earlier point) Internal Clocks  The body’s internal master clock is the suprachiasmatic nucleus (SCN) in the hypothalamus  Axons of special retinal ganglion cells (non-imagine forming cells, NIF) contain a pigment called melanopsin  The SCN is active only during the day regardless of whether a species is diurnal or nocturnal  The SCN helps animals distinguish between day and night, but other structures dictate whether an animal is nocturnal or diurnal in its behavior  The SCN is not dependent on input from other structures to maintain its rhythms o Isolated SCN tissue cultures continued to show rhythmic fluctuations in activity consistent with the source of animal’s previous day-night cycle  When SCN tissue from a short-period hamster is transplanted into a normal hamster, the normal hamster shows the short free-running cycle o When SCN tissue from a normal hamster is transplanted into a short-period hamster, the hamster shows normal 24-hour cycles o In both cases, the behavior of the transplant recipient matches the behavior of the donor  The SCN acts as a master clock that coordinates the activities of other internal, peripheral clocks that exist in most body cells  The rhythms of the SCN are heavily influenced by the presence of light  The peripheral clocks are more easily influenced by daily feeding cycles  Abrupt changes in feeding patterns during the day only can reset the animal’s circadian rhythms by influencing these peripheral clocks  Many travelers attempt to compensate for jet lag by immediately adjusting their mealtimes to their current time zones The Cellular Basis for Circadian Rhythms  The SCN can tell time due to the oscillation of protein production and degradation within a cell  Research with fruit flies allowed researchers to identify 3 separate genes and their protein products that are involved with their cellular circadian rhythms o Per (period) o Tim (timeless) o Clock (circadian locomotor output cycles kaput)  Per and tim proteins inhibit the clock protein whereas clock protein promotes the production of more per and tim proteins  As levels of per and tim proteins increase, inhibition of clock protein ensures that no further per and tim proteins will be produced o As levels of per and tim proteins drop over time, the reduced inhibition of the clock protein results in increased production of more per and tim proteins Biochemistry and Circadian Rhythms  The SCN both regulates and responds to melatonin (an indolamine secreted by the pineal gland)  Melatonin levels are very low during the day, begin to rise in the hours before sleep, and usually peek at about 4:00am when everyone feels really sleepy  Totally blind people experience a melatonin peak at different times each day, leading to sleep difficulties  People with pineal gland tumors or other medical conditions affecting melatonin report sleeping problems  Melatonin release is suppressed by light even if it is dim light such as indoor lighting  Melatonin supplements have been reported to have improve cases of jet lag , shift maladaptation syndrome and other sleep disorders  Treatment with melatonin can be helpful in cases in which visual impairments interfere with normal sleep patterns  Individuals with autism spectrum disorder have low levels of melatonin and often use melatonin supplements to help regulate sleeping patterns  Levels of the hormone cortisol also fluctuates with the pattern of sleeping and waking o Cortisol levels are normally high in the early morning and low at night o Higher levels are associated with higher BP, higher hear rate, and mobilization of the body’s energy stores o Also released during times of stress o Stress-induced high cortisol levels during the night are correlated with poor sleep quality o Might also contribute to the experience of jetlag o Flight crews who cross more than 8 time zones have 1/3 more cortisol in their saliva when compared with ground crews Seasonal Affective Disorder  During the winter months at high altitudes, the reduction in daylight hours can interfere with circadian rhythms  Some people will experience a type of depression called seasonal affective disorder (SAD)  Exact mechanism behind SAD are not known but serotonin levels typically drop in the fall and winter and people are vulnerable to SAD experience more than normal decreases which leads to depression  SAD might also be influenced by disruptions in melatonin release by uneven patterns of daily light  SAD is treated by exposure to bright lights with or without melatonin and antidepressants  Light therapy administered at dawn corrects cases in which people stay up too late, whereas light therapy in the evening helps people who are sleepy too early Stages of Wakefulness and Sleep  Desynchronous brain activity arises from the independent actions of many neurons and is correlated with alertness  Synchronous activity occurs when neurons are firing more in unison and characterizes deep stages of sleep Wakefulness  During wakefulness, EEG recordings alternate between beta wave and alpha wave patterns of brain activity  Beta activity is characterized by highly desynchronized, rapid, irregular, low amplitude waves o Person will be actively thinking and very alert  Alpha waves are slightly slower, larger and more regular than beta waves o Person is awake but quite relaxed  alpha and beta activity alternate throughout periods of wakefulness  periods of high and low alertness during wakefulness follow ultradian cycles of 90-120 minutes in humans Brain Activity During Sleep  sleep consists of alternating periods of rapid eye movement (REM) sleep and non-REM (NREM) sleep  sleep begins when a person enters Stage 1 of NREM sleep  EEG is difficult to distinguish from the waking EEG of a drowsy person  There is some theta wave activity, heart rate and muscle tension begin to decrease o This is occasionally disturbed by a muscle jerk (myoclonia) along with a brief visual image  Stage 2 of NREM sleep accounts for 50% of the night’s entire sleep o Further reductions in heart rate and muscle tension o EEG shows sleep spindles generated by interactions between thalamus and cortex (seen in other stages too) o K complex – brief burst of brain activity (also seen in response to unexpected stimuli) o Spindles and K complexes might reflect the brain’s efforts to keep us asleep while continuing to monitor the external environment  Stage 3 & 4 o Enter after 15 minutes of stage 2 o Body temp, breathing, BP, and heart rate are at very low levels due to the activity of the parasympathetic nervous system o Delta wave activity (largest, slowest, most synchronized waveform of sleeping state) o Stage 4 has more delta waves o Waking up from Stage 4 is more difficult and disorienting  After 90 minutes of NREM, a first period of REM sleep occurs (paradoxical sleep)  Transition from Stage 4 and REM is abrupt but usually involves brief passages through Stage 3 and Stage 2 sleep  REM (Rapid Eye Movement) o In the 8 hour sleep period, average person typically experiences 5 periods of REM o During REM, EEG shows activity similar to beta activity seen during wakefulness with periods of theta activity as well o The eyes make back and forth movements which gives REM sleep its name (Rapid Eye Movement) o Sympathetic nervous system becomes very active o Heart rate, BP and breathing become rapid or irregular o Males experience erections while females experience increased blood flow in the vicinity of the vagina o Major postural muscles are completely inactive effectively paralyzing the sleeper  First 4 hours of sleep are longer periods of NREM and brief periods of REM  Stage 3 and 4 are dominant  REM dominates hours 5-8 of sleep and NREM remains in the lighter stages Sleep Throughout the Life Span  Nightly sleep patterns change as a function of age as well as the composition of sleep  Newborn infants spend 14-16 hours in sleep/day o Half of this time is spent in REM sleep o The more prematurely the child is born, the greater percentage of his or her sleep time is spent in REM th o REM sleep can be recorded for the first time in the fetus at 7 months of pregnancy  By the age of one year, a child’s sleep time has been reduced to 13 hours  Between ages 1-5, most children sleep 8.7 hours  Delta wave activity (stage 3 and 4 NREM) is highest between ages 3-6  At puberty, there is a further slight decrease in REM and a substantial decrease in stages 3 and 4 sleep  NREM sleep declines further as people approach midlife  Around age 50, total sleep time begins to decrease by about 27 minutes per decade into the person’s 80s  Increased awakening accompanies a reduction in sleep spindles with age  Drops in sex hormones associated with aging might be at least partly responsible for some of the age-related changes observed in sleeping patterns  Women approaching menopause frequently experience disruptions in sleep  Sex hormones have a very direct role on the regulation of biorhythms Dreaming During REM and NREM  The discovery that dreams are associated with REM sleep allowed researchers to awaken volunteers and asses the dream experience  Dreaming behavior occurs during both REM sleep and NREM  REM dreams are vivid, lengthy, complicated and storylike, providing us with the sense of firsthand experience with the events taking place  NREM dreams are short episodes characterized by logical single images and a relative lack of emotion  Most dreams appear to be rather ordinary  Most dreams occur in familiar places and involve routine activities  We participate as characters in our dreams only about 15% of the time and imaginary strangers are more likely to appear in our dreams than familiar people  Activation-synthesis theory of dreaming (Hobson and McCarley) – content of dreams reflects ongoing neural activity  When sleeping volunteers were sprinkled with water, they reported dreams of rain and other water0related themes  Dreams of being unable to move in a dangerous situation mirror the muscle paralysis present during the REM state  Common dreams of flying or falling could be caused by the unusual activation of the vestibular system during REM sleep  Dreams with sexual content are consistent with the physical sexual arousal that occurs during REM sleep  Crick and Mitchison proposed a computerized neural network model that sees dreaming as a way for the brain to forget irrelevant info  In Winson`s model, animals evolved the ability to integrate sensory experience with stored memories during REM sleep rather than while awake. Dreaming is just a way to stimulate escape from threatening situations. Animals gain a survival advantage if they can practice dealing with threatening situations in their dreams. The advantages of dreaming could combine some or all of these proposed elements, and further research is needed to clarify the issue  About 70% of our dreams have a negative emotional content  Men report more aggression in their dreams than do women  Viewing upsetting entertainment or reports of natural disaster increases the likelihood of negative dreams  When the content of a REM dream is especially upsetting, we refer to the experience as a nightmare o Appear first when children are between 3-6 and decreases as puberty approaches o Recurring, disturbing nightmares occur in psychological disorders such as PTSD o People troubled by nightmares get trained in lucid dreaming where they are aware that they are in a dream and can control or direct the content of the dream  Night terrors occur in NREM during the first 3 hours of sleep o Between 1-4% of children experience then usually between ages 4-12 o Most episodes begin with an abrupt scream, followed by sweating and an accelerated heartbeat o The sleeper sits upright in bed and stares forward but is not responsive o If awakened, the person shows the disorientation and confusion typically demonstrated when a sleeper is disturbed during very deep NREM o Individuals often report feelings of pressure on the chest, which children interpret as a monster or bear sitting on them o There is usually no memory of the night terror the next day o A genetic predisposition appears to contribute to night terrors: 80% report a family history o Boys experience it more frequently than girls o Adults who experience them are more likely to have been diagnosed with some type of psychopathology, commonly anxiety or personality disorders The Functions of Sleep  Most animals show activity levels that follow circadian rhythms with at least one period of time in which they are relatively quiet and less responsive to external stimuli  In a rare genetic condition, fatal familial insomnia (FFI) middle-aged people gradually lose the ability to sleep and eventually die Sleep Keeps Us Safe  Sleep prevents some animals from being active during parts of the day when they are least safe from predation  The horse is a heavily preyed upon animal in the wild and it generally lives out in the open so the wild horses sleep as little as 1-2 hours per day  Rabbits are also prey but because they have burrows to hide in, they sleep much more than the horse  Predators (such as lions) tend to sleep whenever and wherever they desire for lengthy periods of time Sleep Restores Our Bodies  Sleep (NREM sleep) helps us restore our bo
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