Topic 7

CIRCADIAN RHYTHMS, SLEEP & DREAMS

Circadian rhythm

What is Circadian Rhythms?

Circadian rhythms refer, collectively, to the daily rhythms in physiology and behavior. They control the sleep-wake cycle, modulate physical activity and food consumption, and over the course of the day regulate body temperature, heart rate, muscle tone, and hormone secretion. The rhythms are generated by neural structures in the hypothalamus that function as a biological clock.

Animals and plants possess endogenous clocks to organize daily behavioral and physiological rhythms in accord with the external day-night cycle

The basis for these clocks is believed to be a series of molecular pathways involving “clock” genes that are expressed in a nearly 24-hour rhythm

Refers to circa=approximately, and dias=day

The Influences of Circadian Rhythmso Circadian Rhythm

o A daily rhythmical change in behavior or physiological process.

o About a day o Regular fluctuation from high to low points of certain bodily

functions and behaviors

o Sleep debt o Deficiency caused by not getting the amount of sleep that

one requires for optimal functioning

o Affects psychological functions ofo Blood pressureo Heart rateo Appetiteo Secretion of hormones and digestive enzymeso Sensory acuityo Eliminationo Body’s response to medication

Environmental cues: activity and rest =growth, maintenance, hormonal fluctuations.too

Earths rotation--light-dark cycle, on 24-hour circadian system. Activity-non-activity (circadian rhythms) can be further subdivided up into smaller time activity-rest units,called, ultradian cycles

As wakefulness (alert), stage 1 sleep, stage 2, stage 3 and stage 4 (Non-Rem) and Rem (rapid eye movement sleep), also called active of paradoxical sleep.

About life, students….Its about circles..i.e. cycles…all the

way down…we live inside of circular space..

cycles within cycles within cycles…as in life cycle..sleep cycles, menstrual

cycles, hormonal cycles..time cycles..midnight

(when and where morning and night are simultaneously one, a beginning and an end at the same instant.. Where beginning and ending is the same, is it Friday or Saturday

What’s the Endocrine System?

A collection of glands that secrete hormones in order to regulate functions within the body.

The Influences of Circadian Rhythmso Suprachiasmatic nucleus (SCN)

o A nucleus, situated atop the optic chiasm, in the brain’s hypothalamus that control the timing of circadian rhythms

o It contains a biological clock responsible for organizing many of the body’s circadian rhythms.

o Lesions do not reduce sleep time, but they abolish its circadian periodicity

o Exhibit activity that can be entrained by the light-dark cycleo Transplant SCN, transplant sleep-wake cycle

o Melanopsino A photopigment present in ganglion cells in the retina whose

axons transmit information to the SCN, the thalamus, and the olivary pretectal nuclei.

o Zeitgeberso A stimulus (usually the light of dawn) that resets the biological

clock responsible for circadian rhythms.o Intergeniculate leaflet (IGL)

o A part of the lateral geniculate nucleus that receives information from the retina and projects to the SCN; terminals release neuropeptide Y at the SCN

The Influences of Circadian Rhythmso Control of seasonal rhythms

o Pineal Glando A gland attached to the dorsal tectum; produces

melatonin and plays a role in circadian and seasonal rhythms.

o Secretes melatonin from dusk until just before dawno Does not secrete melatonin during daylight hours

oMelatonino A hormone synthesized from serotonin in the pineal

gland o Secreted during the night by the pineal body; o Melatonin levels display circadian rhythms controlled by

the SCNo plays a role in circadian and seasonal rhythms.o Melatonin is not a sleep aid, but may be used to shift

circadian rhythms

Disruptions in Circadian RhythmsJet lag

o When traveling, you reach your destination at a time when it is daylight there, but it would have been time to go to sleep at the place you started

o Can produce memory deficits that may be permanent

o Supplemental melatonin has been shown to be an effective treatment for relapses of psychiatric disorders induced by jet lag

o Zeitgebers are accelerated or decelerated

o Research indicates that frequent flyers, such as this airline employee, are just as likely to suffer from jet lag when crossing several time zones as travelers who are on their first inter-continental journey.

Disruptions in Circadian RhythmsShift work

o When people work during the night and sleep during the day

o Shift workers average 2 to 4 hours less sleep than nonshift workers of the same age

o Subjective nighto The time during a 24-hour period when body temperature is lowest

and when the biological clock is telling a person to go to sleepo During subjective night, energy and efficiency are at their lowest

point, reaction time is slowest, productivity is diminished, and industrial accidents are significantly higher Zeitgebers unchanged, but sleep-wake cycle must be altered

o Rotating work schedules forward from days to evenings to nights makes adjustment easier because people find it easier to go to bed later and wake up later than the reverse

o Modafinilo A wakefulness drug that will help people remain alert without the

side effects of stimulants such as caffeine

Can the effects be prevented or minimized?o Both produce a variety of deficitso Can the effects be prevented or minimized?

Reducing Jet Lag Gradually shift sleep-wake cycle prior to travel Administer post-flight treatments to promote the needed shift

Phase advance following east-bound travel with intense light early in the morning

Hamster studies suggest a good early morning workout may also help

Can the effects be prevented or minimized?

Reducing the Effect of Shift Changes Schedule phase delays, rather than phase advances

Move from current schedule to one that starts later It is easier to stay up later and get up later than to retire and

arise earlier Phase advances are harder, explaining why east-bound

travel tends to be more problematicShift workers who temporarily reside at their work

places, such as workers on offshore oil rigs, appear to adjust more easily to the demands of night work than those who live at home

Exposure to appropriately timed bright light or even light of medium intensity has been found to reset young adults’ biological clocks and improve their performance

The Influences of Circadian Rhythms

Disruptions in Circadian Rhythmso Subjective night

o The time during a 24-hour period when the biological clock is telling a person to go to sleep.

o Energy and efficiency are at their lowest pointso Reaction time is slowesto Productivity is diminishedo Industrial accidents are highero Daylight savings time in spring is associated with short

term 6.5% increase in accidental deaths.

o Work scheduleso Moving work schedules forward from days to evenings

to nights makes adjustment easiero Rotating shifts every three weeks lessens the effect on

sleep

SLEEP

SleepWhat is it? What Does It Look Like? How does it function? What happens when we sleep?

Measurement? How does it change with age?

What is sleep?A state of

sustained immobility or quiescence in a characteristic posture accompanied by reduced responsivity to external stimuli;

Immobility need not be absolute as dolphins, seals and whales may float or swim while asleep…most sleep with eyes closed but not all;

Cattle may sleep with eyes open..horses and elephants sleep while standing…

Why do we sleep?The answer: no one really knows for sure! Some believe that sleep:

gives the body a chance to gain strength from the day's activities but in reality, the amount of energy saved by sleeping for even eight hours is tiny - about 50 kilocalories, the same amount of energy in a piece of toast!

We have to sleep because it is needed to sustaining normal levels of cognitive skills such as speech, memory, and innovative and flexible thinking. sleep plays an important part in brain

development.

Why Do We Sleep?

Proximate Explanation:Because we begin to

“feel” tired..melatonin Need to consolidate

energy and experiences;

Need to avoid predators;

Need to restore body cells and promote protein anabolism;

Maintain hormonal secretions, immune function

Ultimate Explanationsustains our

ability to reproduce successfully, by maintaining good health

Why do we sleep?

Recuperation theoriesSleep is needed to restore homeostasisWakefulness causes a deviation from

homeostasis

Circadian theoriesSleep is the result of an internal timing

mechanismSleep evolved to protect us from the dangers of

the night

What Happens When We Don’t Sleep?A good way to understand the role of sleep is to look at what

would happen if we didn't sleep. Lack of sleep:

Serious effects on our brain’s ability to function (cognitive functioning) If you have ever not slept for an entire night, you'll feel

grumpy, groggy, irritable and forgetful. After just one night without sleep, concentration becomes more difficult and attention span shortens a great deal.

Continues lack of sufficient sleep the part of the brain that controls language, memory, planning and sense of time is severely affected, practically shutting down. 17 hours of continuous sleeplessness leads to a decrease in

performance that is equivalent to a blood alcohol level of two glasses of wine(0.05%).

Effect on emotional and physical health – excessive daytime sleepiness - linked to stress and high

blood pressure. may increase the risk of obesity because chemicals and

hormones that play a key role in controlling appetite and weight gain are released during sleep.

What happens when we sleep?

What happens every time we get a bit of shut eye?

Sleep occurs in a recurring cycle of 90 to 110

minutes and is divided into two categories:

Non-REM (which is further split into four stages)

Stage 1:half awake and half asleep (light sleep)

Stage 2: The breathing pattern and heart rate

start to slow down.

Stage 3: Brain begins to produce delta waves

Stage 4: Rhythmic breathing and limited muscle

activity.

REM (Rapid Eye Movement) sleep.

NREM Sleepo Non-rapid eye movement

sleep.o Four sleep stages1. Lightest sleep2. Mid-sleep3. Deep sleep4. Deepest sleep

o Heart and respiration slow and regular

o Little body movemento Blood pressure and brain

activity at lowest points of 24 hour period.

Non-REM sleepStage 1:Half awake & half asleep. A transition period of

drowsiness between waking & sleeping. Slow rolling eye movements. Body temperature drop. Muscle activity slows down, Heart rate slows and slight twitching may occur. The period of light sleep (we can be awakened easily at this stage). (10 min)

Stage 2: Lasts around 20 minutes. The breathing pattern and heart rate start to slow down. Somewhat more deeply asleep. This period accounts for the largest part of human sleep.

Stage 3: Brain begins to produce delta waves [a type of wave that is large (high amplitude) and slow (low frequency) - Delta waves reach 20%]. Slow wave sleep begins. Breathing and heart rate are at their lowest levels.

Stage 4: Rhythmic breathing and limited muscle activity. If we are awakened during deep sleep we do not adjust immediately and often feel groggy and disoriented for several minutes after waking up. Some children experience bed-wetting, night terrors, or sleepwalking during this stage. Delta waves reach nearly 100%.

REM (Rapid Eye Movement) sleep

The first Rapid Eye Movement (REM) period usually begins about 70 to 90 minutes after we fall asleep. We have around three to five REM

occurrences a night.Although we are not conscious, the brain is

very active - often more so than when we are awake. This is the period when most dreams

occur. Our eyes dart around, and our breathing rate and blood pressure rise.

However, our bodies are effectively paralyzed nature's way of preventing us from acting out our dreams.

After REM sleep, the whole cycle begins again.

REM SleepoRapid eye movement sleep - also known as “active sleep”.20-25% of a night’s sleep

oInternally:oIntense brain activityoBrain metabolism increasesoBrain temperature rises rapidlyoEpinephrine release leads to increases in Blood pressure, Heart rate, respiration

oExternally:o Body appears calmo Large muscles become paralyzedo Eyes dart aroundo Dreaming occurs in 80% of peopleo Brain conducts -Consolidation of learning (all night studying doesn’t help)

o perceptual skills increase after 8-10 hours of sleepo Memory consolidation

REM Reboundo The increased amount of REM sleep that

occurs after REM deprivationo Intensity of REM sleep increaseso Those with Sleep Deprivation

oProceed more rapidly into REM as REM deprivation increases

oMore time spent in REM when deprivation is over

o Often associated with unpleasant dreams or nightmares

o Alcohol, amphetamines, cocaine, and LSD use suppress REM sleep results in REM rebound

o Withdrawal results in REM reboundsREM rebound suggests that REM sleep serves a

special function

Purpose of REM?Necessary for mental health

Inconsistent with the effects of tricyclic antidepressants – block REM

Necessary for maintenance of normal levels of motivation

Necessary for processing of memoriesNo clear purpose

Default Theory of REMREM serves no critical functionOne can’t stay continuously in non-REM sleep, so we

switch between REM and wakefulnessWhen bodily needs exist – wake upNo immediate needs – REMNo REM rebound seen when lost REM periods replaced

with 15-mins awake

How much sleep is required?

There is no set amount of time that everyone needs to sleep, since it varies from person to person.

Results from the sleep profiler indicate that people like to sleep anywhere between 5 and 11 hours, with the average being 7.75 hours

How long people sleep a day on average:

Variations in Sleepo Infants and young children

o have the longest sleep timeo Have the highest of REM and slow

wave sleep

o Ages 6-pubertyo Most consistent sleepers and wakerso Sleep and awake same time daily

o Adolescentso Sleep patterns are influenced by their

scheduleso Sleep longer when no schedule

conflictso Poor sleep may contribute to poor

school performance

Variations in SleepLarks and owls

LarksAwaken early every morning and leap out of

bed with enthusiasm, eager to start the dayBody temperature rises rapidly after they

awaken and stays high until about 7:30 p.m.Turn in early and have the fewest sleep

problems

Variations in SleepOwls

Fumble for the alarm clock and push the snooze button to get a few more precious minutes of sleep

Body temperature of an owl gradually rises throughout the day, peaking in the afternoon and not dropping until later in the evening

Guthrie and others Compared the performance of several hundred college

students classified as larks or owls Found that the larks made better grades in early morning

classes, while the owls made higher grades in classes they took later in the day

A gene that runs the biological clock is responsible, in part, for the differences between larks and owls

Animal Sleep

SPECIESAverage total sleep

time per day

Python 18 hours

Tiger 15.8 hours

Cat 12.1 hours

Chimpanzee 9.7 hours

Sheep 3.8 hours

African Elephant 3.3 hours

Giraffe 1.9 hours

Animals also have a required certain amount of sleep:

Sleepo Understanding of sleep increased by the study

ofoBrain wavesoEye movementsoChin muscle tensionoHeart rateoRespiration rate

Electro-oculogram (EOG)An electrical potential from the eyes, recorded by

means of electrodes placed on the skin around them; detects eye movements.

Electromyogram (EMG)An electrical potential recorded from an

electrode placed on a muscle.

3 Physiological Measures of Sleep

By means of Electroencephalogram (EEG)“brain waves”

By means of EOGEye movements seen during rapid eye

movement (REM) sleep

By means of EMGLoss of activity in neck muscles during

some sleep stages

SleepPolysomnogram o Provides brain wave sleep recordings

o Outlined REM and NREM sleep patterns

Beta activity - Irregular electrical activity of 13–30 Hz recorded from the brain; generally associated with a state of arousal.

Alpha activity- A smooth electrical activity of 8–12 Hz recorded from the brain; generally associated with a state of relaxation Eyes closed, preparing to sleep

Theta activity - EEG activity of 3.5-7.5 Hz that occurs intermittently during early stages of slow-wave and REM sleep.

Delta activity - Regular, synchronous electrical activity of less than 4 Hz recorded from the brain; occurs during the deepest stages of slow-wave sleep.

EEG

Stage 1 similar to awake EEG, but slower low-voltage, high-frequency

EEG voltage increases and frequency decreases as one progresses from stage 1 through 2, 3, and 4

Stage 2 – characterized by K complexes – large negative waves Sleep spindles – burst of 12-14 Hz waves

Stages 3 and 4 – delta waves, large and slow Progress to stage 4 sleep and then retreat to

stage 1

Sleep Cycle & EEG

Emergent stage 1 differs from initial stage 1 REMs Loss of body core muscle tone

Progress through sleep stages in 90 minute cycles

More time spent in emergent stage 1 as night progresses

Emergent stage 1 sleep = REM sleep Non-REM (NREM) sleep = all other stages

Stage 3 + 4 = slow-wave sleep (SWS) During REM: REMs, loss of core muscle tone, low-

amplitude/high-frequency EEG, increased cerebral and autonomic activity, muscles may twitch

Sleep Cycle & EEG

Physiological Mechanisms of Sleep and Waking

Types of neurotransmitter involved1. Acetylcholine -Two groups of acetylcholinergic

neurons located in the pons and basal forebrain. They produce activation and cortical desynchrony when they are stimulated.

2. Norepinephrine- Catecholamine agonists produce arousal and sleeplessness; effects appear to be mediated by the locus coeruleus in the dorsal pons.

3. Serotonin (5-HT) - Appears to play a role in activating behavior; almost all of the brain’s serotonergic neurons are found in the raphe nucleus. These neurons are located in the medullary and pontine regions of the brain.

4. Histamine - A neurotransmitter implicated in the control of wakefulness and arousal; a compound synthesized from histidine, an amino acid.

Physiological Mechanisms of Sleep and Waking

Neural control of arousal

Locus coeruleusA dark color group of noradrenergic cell bodies located in the pons

near the rostral end of the floor of the fourth ventricle; involved in arousal and vigilance.

Raphe nucleusA group of nuclei located in the reticular formation of the medulla,

pons, and midbrain, situated along the midline; contains serotonergic neurons.

Physiological Mechanisms of Sleep and Waking

Neural control of arousal

Tuberomammillary nucleusA nucleus in the ventral posterior

hypothalamus, just rostral to the mammillary bodies; contains histaminergic neurons involved in cortical activation and behavioral arousal.

HypocretinA peptide also known as orexin, produced by

neurons whose cell bodies are located in the hypothalamus; their destruction causes narcolepsy.

Physiological Mechanisms of Sleep and Waking

Neural control of slow-wave sleep

Ventrolateral preoptic area (VLPA)A group of GABAergic neurons in the

preoptic area whose activity suppresses alertness and behavioral arousal and promotes sleep.

Destruction of this area has been reported to resultin total insomnia, coma, and eventual death in rats.

Physiological Mechanisms of Sleep and Waking

Neural control of REM sleep

PGO wave (pontine, geniculate, occipital):Bursts of phasic

electrical activity originating in the pons, followed by activity in the lateral geniculate nucleus and visual cortex, a characteristic of REM sleep.

Physiological Mechanisms of Sleep and WakingThe executive mechanism

Peribrachial area -The region around the brachium conjunctivum, located in the dorsolateral pons; contains acetylcholinergic neurons involved in the initiation of REM sleep.

Carbachol - A drug that stimulates acetylcholine receptors.Medial pontine reticular formation (MPRF)-A region that

contains neurons involved in the initiation of REM sleep; activated by acetylcholinergic neurons of the peribrachial area.Similarities between REM and wakefulness suggest that the

same brain area might be involved in bothREM sleep is controlled by nuclei in the caudal reticular

formation, each controlling a different aspect of REMMagnocellular nucleus - A nucleus in the medulla; involved

in the atonia (muscular paralysis) that accompanies REM sleep.

Effects of Sleep Deprivationo Causes

o Difficulty concentratingo Attention lapseo General irritability o Decreases cognitive functioningo Impairs learning

Recuperation theories predict:Long periods of wakefulness will result in

disturbancesDisturbances will get worse as deprivation

continuesAfter deprivation, much of the missed

sleep will be regained What does the research indicate?

Studies of Sleep Deprivation in Humans

Does sleep loss affect your performance?

We tend to be poor judges of the effects of sleep deprivation on our performance

3-4 hours of deprivation in one nightIncreased sleepinessDisturbances displayed on

written tests of moodPerform poorly on tests of

vigilance

2-3 days of continuous deprivation Experience microsleeps,

naps of 2-3 seconds Effects on complex

cognitive function, motor performance, and physiological function are less consistent

Sleep-Deprivation Studies with Lab Animals

Carousel apparatus used to deprive rats of sleepWhen the experimental

rat’s EEG indicates sleep, the chamber floor moves – if the rat does not awaken, it falls into water

Yoked controls – subjected to the same floor rotations

Experimental rats typically die after several days

Postmortem studies reveal the extreme stress experienced by the experimental rats

Carousel apparatus

Theories of Sleep Functiono Restorative theory, holds that being

awake produces wear and tear on the body and brain, and sleep serves the function of restoring the body and mind.

o Circadian theory of sleep is based on the premise that sleep evolved to keep humans out of harm’s way during the dark of night and possibly from becoming prey of some nocturnal predator.

Hypothalamus and SleepDuring WWI – victims of

encephalitis lethargica caused some to sleep continuously and others to sleep little

Damage in posterior hypothalamus and adjacent midbrain > excessive sleep

Damage in preoptic area and adjacent forebrain > wakefulness

DREAM

Dreams Dream content

Varies by culture, gender, and ageFrequently connects with recent experienceMay help us form memories

o REM Dreamo An almost continually occurring dream during REM sleepo Has story like qualitieso More vivid, visual, and emotional than NREM dreams

o NREM Dreamo Less frequent than REM dreamso Less memorable than REM dreams

o Bizarre Dreamso Biopsychological explanation

o Lower amounts of serotonin and norepinephrine lead to less inhibition of impulsive thoughts and actions.

o Lucid Dreamso A dream an individual is aware of dreaming and whose content

the individual is often able to influence while dreaming.

Lucid DreamsNext time you wake up during a dream, try the following the steps to see if you can engage in lucid dreaming.1.Relax2.Close your eyes and focus on an imaginary spot in your field of vision.3.Focus on your intention to have a lucid dream4.Tell yourself that you’re going to dream about whatever you want.5.Imagine yourself in a dream of the type you want to have.6.Repeat the steps until you fall asleep.

Interpreting Dreamso Sigmund Freudo Freud thought dreams were triggered by

unacceptable repressed wisheso Believed dreams satisfy unconscious sexual

and aggressive desires and so must be disguised.o Manifest Content – what we experience

o The content of a dream as recalled by the dreamer

o Latent Content o The underlying meaning of the dream

o In recent yearso Seen as an expression of a broad range of the

dreamer’s concerns rather than sexual impulses.

Interpreting Dreamso Activation-Synthesis

Hypothesiso Dreams are the brain’s

attempt to make sense of the random firing of brain cells during sleep.

Cortex creates a story in an effort to make sense of the brain’s activity

Story is synthesized as a consequence of brain activity

o People impose meaning on the random mental activity

Sleep Disorders - Parasomniaso Somnambulism (sleepwalking)

o occurs during partial arousal from stage 4 sleep.o Sleep terror

o happens during partial arousal from stage 4 sleep o usually begins with a piercing scream.

o Nightmares o are frightening dreams that occur during REM

sleep.o Somniloquy (Sleeptalking)

o occurs during any sleep stageo is more frequent among children.

Major Sleep Disorderso Insomnia

A sleep disorder characterized by Disorders of sleep initiation and

maintenanceo Difficulty falling or staying asleepo Waking too earlyo Sleep that is light, restless, or of poor

quality Symptoms can lead to distress and

impairment in daytime functioning

o Hypersomnia o Disorders of excessive sleep or sleepiness

Major Sleep Disorderso Sleep apnea

Periods during sleep when breathing stops and the individual must awaken briefly in order to breatheo 2 types

1. Caused by muscle spasms or atonia2. Failure of the CNS to stimulate breathing

Most commonly seen in males, the overweight, and in the elderly

The major symptoms are excessive daytime sleepiness and extremely loud snoring, often accompanied by snorts, gasps, and choking noises

Alcohol and sedatives aggravate the condition Can lead to chronic high blood pressure, heart

problems, and even death Neuroscientists have also found that it can cause mild

brain damage The interrupted sleep experienced by individuals with

this disorder affects cognitive as well as physiological functioning

Major Sleep Disorderso Narcolepsy

o Also a form of hypersomniao Characterized by excessive daytime sleepiness and

repeated brief uncontrollable attacks of daytime REM sleep, usually lasting 10 – 20 minutes

o An incurable sleep disorder o Cataplexy – loss of muscle tone while awakeo Sleep paralysis – paralyzed while falling asleep or upon

wakingo Hypnagogic hallucinations – dreaming while awakeo Appears to be an abnormality in the mechanisms that

triggers REMo Dreaming and loss of muscle tone while awake –

suggest REM intruding into wakefulnesso REM without atonia – able to act out dreams – possibly

caused by damage to the nucleus magnocellularis or its output

Effects of Long-Term Sleep Reduction The brain is adaptable – may be able to

function well with very little sleep One deficit seen with subjects sleeping only

5.5 hours for 60 days Slight deficit in a test of auditory vigilance

Other study – no ill effects seen at I year with subjects sleeping 7-18 hours less per week than before study

How much sleep do you need? Can this question be answered? Why or why not?