Chapter 9Chapter 9

Sleep and Biological RhythmsSleep and Biological Rhythms

Stages of sleepStages of sleep

► Most sleep research conducted in a sleep laboratoryMost sleep research conducted in a sleep laboratory► Attaches electrodes to measure EEG, EMG (Attaches electrodes to measure EEG, EMG (electromyogramelectromyogram; ;

to measure muscle activity), and EOG (to measure muscle activity), and EOG (electro-oculogramelectro-oculogram; to ; to measure eye movements)measure eye movements)

► EEG stagesEEG stages AwakeAwake

► Alpha activityAlpha activity – smooth electrical activity of 8-12 Hz recorded from the – smooth electrical activity of 8-12 Hz recorded from the brain; state of relaxationbrain; state of relaxation

► Beta activityBeta activity – irregular electrical activity of 13-30 Hz recorded from – irregular electrical activity of 13-30 Hz recorded from the brain; state of arousalthe brain; state of arousal

Stage 1 sleepStage 1 sleep► Transition b/t sleep and wakefulnessTransition b/t sleep and wakefulness► Theta activityTheta activity – EEG activity of 3.5-7.5 Hz that occurs intermittently – EEG activity of 3.5-7.5 Hz that occurs intermittently

during early stages of slow-wave sleep and REM sleepduring early stages of slow-wave sleep and REM sleep

Stages of sleepStages of sleep

► EEG stagesEEG stages Stage 2 sleepStage 2 sleep

► EEG is generally irregular but contains periods of theta activity, EEG is generally irregular but contains periods of theta activity, sleep spindlessleep spindles and and K complexesK complexes

► Some experimenters believe that sleep spindles represent the activity of a Some experimenters believe that sleep spindles represent the activity of a mechanism that is involved in keeping a person asleepmechanism that is involved in keeping a person asleep

Stage 3 & 4 sleepStage 3 & 4 sleep► Delta activityDelta activity – regular, synchronous electrical activity of less than 4 Hz – regular, synchronous electrical activity of less than 4 Hz

recorded from the brain; occurs during the deepest stages of slow-wave sleeprecorded from the brain; occurs during the deepest stages of slow-wave sleep REM sleepREM sleep – a period of desynchronized EEG activity during sleep, at – a period of desynchronized EEG activity during sleep, at

which time dreaming, rapid eye movements, and muscular paralysis occurwhich time dreaming, rapid eye movements, and muscular paralysis occur► Dreaming during this state; tend to be narrative in formDreaming during this state; tend to be narrative in form

Stages 1-4 referred to as Stages 1-4 referred to as non-REM sleepnon-REM sleep Stages 3-4 referred to as Stages 3-4 referred to as slow-wave sleepslow-wave sleep During rest of the night subject will alternate b/t periods of non-REM sleep During rest of the night subject will alternate b/t periods of non-REM sleep

and REM sleep, each cycle about 90 min long, containing ~20-30 min of and REM sleep, each cycle about 90 min long, containing ~20-30 min of REM sleepREM sleep

Stages of sleepStages of sleep

► The fact that REM sleep occurs at regular 90-minute intervals The fact that REM sleep occurs at regular 90-minute intervals suggests that a brain mechanism alternately causes REM and suggests that a brain mechanism alternately causes REM and slow-wave sleepslow-wave sleep

► The cyclic nature of REM sleep appears to be controlled by a The cyclic nature of REM sleep appears to be controlled by a “clock” in the brain that also controls an activity cycle that “clock” in the brain that also controls an activity cycle that continues through wakingcontinues through waking

► Basic rest-activity cycleBasic rest-activity cycle – a 90-mn cycle (in humans) of – a 90-mn cycle (in humans) of waxing and waning alertness; controlled by a biological clock waxing and waning alertness; controlled by a biological clock in the caudal brain stem; controls cycles of REM sleep and in the caudal brain stem; controls cycles of REM sleep and slow-wave sleepslow-wave sleep

► REM sleep also includes lack of muscle tonus, penile erection REM sleep also includes lack of muscle tonus, penile erection or vaginal secretionor vaginal secretion

Mental activity during sleepMental activity during sleep

► Cerebral blood flow in the human brain during REM sleep is Cerebral blood flow in the human brain during REM sleep is high in the visual association cortex but low in the inferior high in the visual association cortex but low in the inferior frontal cortex (concerned with planning, strategies)frontal cortex (concerned with planning, strategies)

► Eye movements during REM sleep may be related to the Eye movements during REM sleep may be related to the visual imagery that occurs while we dreamvisual imagery that occurs while we dream

► Particular brain mechanisms that become active during a Particular brain mechanisms that become active during a dream are those that would become active if the events in the dream are those that would become active if the events in the dream were actually occurringdream were actually occurring

Disorders of sleepDisorders of sleep

► InsomniaInsomnia Affects ~20% of popAffects ~20% of pop One of the most important causes of insomnia is sleeping medication, One of the most important causes of insomnia is sleeping medication,

because of developed tolerance and withdrawal symptomsbecause of developed tolerance and withdrawal symptoms► Drug dependency insomniaDrug dependency insomnia – caused by the side effects of ever-increasing doss of – caused by the side effects of ever-increasing doss of

sleeping medicationssleeping medications Unreliability of self-reports; sleep studies help doctors prescribe correctlyUnreliability of self-reports; sleep studies help doctors prescribe correctly Sleep apneaSleep apnea – cessation of breathing while sleeping; mostly caused by an – cessation of breathing while sleeping; mostly caused by an

obstruction of the airway that can be corrected surgically or by a breathing obstruction of the airway that can be corrected surgically or by a breathing maskmask

► NarcolepsyNarcolepsy Characterized by periods of irresistible sleep, attacks of cataplexy (complete Characterized by periods of irresistible sleep, attacks of cataplexy (complete

paralysis that occurs during waking), sleep paralysis (paralysis occurring paralysis that occurs during waking), sleep paralysis (paralysis occurring before falling asleep), and hypnagogic hallucinations (vivid dreams that occur before falling asleep), and hypnagogic hallucinations (vivid dreams that occur just before a person falls asleep)just before a person falls asleep)

Produced by a brain abnormality that disrupts the neural mechanisms that Produced by a brain abnormality that disrupts the neural mechanisms that control various aspects of sleep and arousalcontrol various aspects of sleep and arousal

Disorders of sleepDisorders of sleep

► Narcolepsy con’tNarcolepsy con’t Human narcolepsy is a genetic disorder that is influenced by Human narcolepsy is a genetic disorder that is influenced by

unknown env’tal factorsunknown env’tal factors There is a mutation of the gene that codes for a receptor for the There is a mutation of the gene that codes for a receptor for the

peptide peptide hypocretinhypocretin (aka orexin), which is produced by neurons in (aka orexin), which is produced by neurons in the hypothalamusthe hypothalamus

► REM sleep behavior disorderREM sleep behavior disorder A neurological disorder in which the person does not become A neurological disorder in which the person does not become

paralyzed during REM sleep and thus acts out dreamsparalyzed during REM sleep and thus acts out dreams Appears to be a neurodegenerative disorder with at least some Appears to be a neurodegenerative disorder with at least some

genetic componentgenetic component

Why do we sleep?Why do we sleep?

► Functions of slow-wave sleepFunctions of slow-wave sleep Researchers believe the primary function of slow-wave sleep is to Researchers believe the primary function of slow-wave sleep is to

permit the brain to restpermit the brain to rest Essential for survival (even seen in species where it would seem Essential for survival (even seen in species where it would seem

dangerous to sleep)dangerous to sleep) Effects of sleep deprivationEffects of sleep deprivation

► Sleep deprivation has not been shown to be necessary for the body to Sleep deprivation has not been shown to be necessary for the body to function properlyfunction properly

► However, cognitive functions are affectedHowever, cognitive functions are affected► Fatal familial insomniaFatal familial insomnia – characterized by progressive insomnia, – characterized by progressive insomnia,

results in damage to the thalamusresults in damage to the thalamus► Lab rats forced to remain awake eat more, but lose weight (due to Lab rats forced to remain awake eat more, but lose weight (due to

increased metabolism) and eventually dieincreased metabolism) and eventually die Effects of exercise on sleepEffects of exercise on sleep

► No changes in slow-wave or REM sleep in subjects on bed-rest No changes in slow-wave or REM sleep in subjects on bed-rest

Why do we sleep?Why do we sleep?

► Functions of slow-wave sleep con’tFunctions of slow-wave sleep con’t Effects of mental activity on sleepEffects of mental activity on sleep

► Increased mental activity causes subjects to experience increased Increased mental activity causes subjects to experience increased slow-wave (especially Stage 4) sleepslow-wave (especially Stage 4) sleep

► Functions of REM sleepFunctions of REM sleep After several days of REM sleep deprivation, subjects would show After several days of REM sleep deprivation, subjects would show

a a rebound phenomenonrebound phenomenon (increase of normal percentage of REM (increase of normal percentage of REM sleep) when permitted to sleep normallysleep) when permitted to sleep normally

The highest proportion of REM sleep is seen during the most The highest proportion of REM sleep is seen during the most active phase of brain developmentactive phase of brain development► So why do adults have REM sleep then?So why do adults have REM sleep then?► Maybe to facilitate modest brain changes due to learningMaybe to facilitate modest brain changes due to learning

Studies with lab animals demonstrate that REM sleep does indeed Studies with lab animals demonstrate that REM sleep does indeed facilitate learningfacilitate learning

In humans, learning can affect the amount of REM sleep a person In humans, learning can affect the amount of REM sleep a person obtainsobtains

Chemical control of sleepChemical control of sleep

► Since sleep is regulated, the body must either produce a Since sleep is regulated, the body must either produce a sleep-promoting substance or a wakefulness-promoting sleep-promoting substance or a wakefulness-promoting substancesubstance

► Suggested that Suggested that adenosineadenosine may play a role in the control of may play a role in the control of sleep, by increasing the amount of delta activity during sleepsleep, by increasing the amount of delta activity during sleep

► Neural control of arousalNeural control of arousal AcetylcholineAcetylcholine

► ACh antagonists decrease EEG signs of cortical arousal while agonists ACh antagonists decrease EEG signs of cortical arousal while agonists increase themincrease them

► Activation of cerebral cortex and increased release of ACh stimulated Activation of cerebral cortex and increased release of ACh stimulated by a group of ACh neurons located in basal forebrainby a group of ACh neurons located in basal forebrain

NorepinephrineNorepinephrine► Locus coeruleusLocus coeruleus – a dark-colored group of NE cell bodies located in the – a dark-colored group of NE cell bodies located in the

pons near the rostral end of the floor of the 4pons near the rostral end of the floor of the 4thth ventricle; involved in ventricle; involved in arousal and vigilancearousal and vigilance

► NE increases an animal’s ability to pay attention to stimuli in the env’tNE increases an animal’s ability to pay attention to stimuli in the env’t

Activity of NE neurons in LCActivity of NE neurons in LC

Chemical control of sleepChemical control of sleep

► Neural control of arousal con’tNeural control of arousal con’t SerotoninSerotonin

► Most of the brain’s 5-HT neurons are located in raphe nuclei, Most of the brain’s 5-HT neurons are located in raphe nuclei, which is located in the medullary and pontine regiond of the which is located in the medullary and pontine regiond of the reticular formationreticular formation

► Stimulation of the neurons causes locomotion and cortical Stimulation of the neurons causes locomotion and cortical arousalarousal

► 5-HT neurons in raphe nuclei activated highly during awake 5-HT neurons in raphe nuclei activated highly during awake states, and less during deep stages of sleepstates, and less during deep stages of sleep

5-HT neurons in raphe nuclei5-HT neurons in raphe nuclei

Activity of 5-HT neurons in Activity of 5-HT neurons in raphe nucleiraphe nuclei

Chemical control of sleepChemical control of sleep

HistamineHistamine► Cell bodies of histaminergic neurons located in Cell bodies of histaminergic neurons located in tuberomammillary tuberomammillary

nucleusnucleus of the hypothalamus of the hypothalamus► Project to cerebral cortex, and increase cortical activation and arousalProject to cerebral cortex, and increase cortical activation and arousal

HypocretinHypocretin► Cell bodies of neurons that secrete hypocretin are located in the Cell bodies of neurons that secrete hypocretin are located in the

lateral hypothalamus and terminate in several regions involved in lateral hypothalamus and terminate in several regions involved in arousalarousal

► Has an excitatory, wakefulness-promoting effectHas an excitatory, wakefulness-promoting effect

Chemical control of sleepChemical control of sleep

► Neural control of slow-wave sleepNeural control of slow-wave sleep One region important: One region important: ventrolateral preoptic areaventrolateral preoptic area (VLPA), rostral to (VLPA), rostral to

the hypothalamus; destruction of this area produced total insomnia the hypothalamus; destruction of this area produced total insomnia in ratsin rats

Contains inhibitory GABA-secreting neurons and these neurons send Contains inhibitory GABA-secreting neurons and these neurons send their axons to the tuberomammillary nucleus, dorsal pons, raphe their axons to the tuberomammillary nucleus, dorsal pons, raphe nuclei, and locus coeruleusnuclei, and locus coeruleus

Also receives inhibitory info from these regions, creating a flip-flop Also receives inhibitory info from these regions, creating a flip-flop effect of either awake or sleep stateseffect of either awake or sleep states

► Neural control of REM sleepNeural control of REM sleep In lab animals, REM sleep also creates In lab animals, REM sleep also creates PGO wavesPGO waves (pons, genicultae, (pons, genicultae,

occipital) in addition to EEG activity, muscular paralysis, etcoccipital) in addition to EEG activity, muscular paralysis, etc PGO waves are bursts of phasic electrical activity originating in the PGO waves are bursts of phasic electrical activity originating in the

pons followed by activity in the LGN and visual cortexpons followed by activity in the LGN and visual cortex REM sleep controlled by mechanisms located within the pons:REM sleep controlled by mechanisms located within the pons:

► The executive mechanismThe executive mechanism ACh neurons located in dorsolateral pons (ACh neurons located in dorsolateral pons (peribrachial areaperibrachial area) trigger the onset ) trigger the onset

of REM sleepof REM sleep

Chemical control of sleepChemical control of sleep

► Neural control of REM sleep (con’t)Neural control of REM sleep (con’t) The executive mechanismThe executive mechanism

► Activation of single neurons in this area are related to the sleep cycleActivation of single neurons in this area are related to the sleep cycle► Axons of these neurons project to the reticular formation, forebrain, Axons of these neurons project to the reticular formation, forebrain,

brain stem regions that control eye movementsbrain stem regions that control eye movements► CarbacholCarbachol, an ACh receptor agonist, when infused into the reticular , an ACh receptor agonist, when infused into the reticular

formation, produces REM sleep in lab animalsformation, produces REM sleep in lab animals► Magnocellular nucleusMagnocellular nucleus – locaed in the medulla; involved in the – locaed in the medulla; involved in the

muscular paralysis during REM sleepmuscular paralysis during REM sleep 5-HT and NE5-HT and NE

► Activity of neurons in the dorsal raphe nucleus and locus coeruleus Activity of neurons in the dorsal raphe nucleus and locus coeruleus normally inhibits REM sleep and a reduction in firing rate may trigger normally inhibits REM sleep and a reduction in firing rate may trigger a bout of REM sleepa bout of REM sleep

Biological clocksBiological clocks

► Daily rhythms in behavior and physiological processes called Daily rhythms in behavior and physiological processes called circadian circadian rhythmsrhythms; some are passive responses to changes in illumination, while ; some are passive responses to changes in illumination, while others are controlled by mechanisms within the organismothers are controlled by mechanisms within the organism

► 24 hour period for plants and animals24 hour period for plants and animals► ZeitgeberZeitgeber – a stimulus (usually the light of dawn) that resets the – a stimulus (usually the light of dawn) that resets the

biological clock that is responsible for circadian rhythmsbiological clock that is responsible for circadian rhythms► Superchiasmatic nucleusSuperchiasmatic nucleus – situated atop the optic chiasm; contains a – situated atop the optic chiasm; contains a

biological clock that is responsible for organizing many of the body’s biological clock that is responsible for organizing many of the body’s rhythmsrhythms activity, drinking, hormonal secretion, sleep cycles, feedingactivity, drinking, hormonal secretion, sleep cycles, feeding Receive projections from the retina (retinohypothalamic pathway)Receive projections from the retina (retinohypothalamic pathway) Photoreceptors provide SCN with info about light levels (via use of the Photoreceptors provide SCN with info about light levels (via use of the

chemical chemical melanopsinmelanopsin)) SCN also receives light info from SCN also receives light info from Intergeniculate leafletIntergeniculate leaflet (part of the LGN) (part of the LGN) Neurons of the SCN project to the midbrain, hypothalamic nuclei and others Neurons of the SCN project to the midbrain, hypothalamic nuclei and others

in order to control eating, drinking, sleep cycles, and hormone secretionin order to control eating, drinking, sleep cycles, and hormone secretion

Biological clocksBiological clocks

► SCN contains a biological clockSCN contains a biological clock► Evidence suggests that each neuron in the SCN contains a Evidence suggests that each neuron in the SCN contains a

“clock”“clock”► Clock “ticking” is provided by the production and breakdown Clock “ticking” is provided by the production and breakdown

of a protein that acts back on the genes responsible for their of a protein that acts back on the genes responsible for their own production; thus creating a cycleown production; thus creating a cycle

Control of seasonal rhythmsControl of seasonal rhythms

► The pineal gland and melatoninThe pineal gland and melatonin Pineal glandPineal gland – sits on top of the midbrain; produces melatonin – sits on top of the midbrain; produces melatonin

and plays a role in circadian and seasonal rhythmsand plays a role in circadian and seasonal rhythms MelatoninMelatonin is secreted at night and controls hormones, is secreted at night and controls hormones,

physiological processes and behaviors that show seasonal physiological processes and behaviors that show seasonal variations (e.g. hibernation)variations (e.g. hibernation)

Changes in circadian rhythmsChanges in circadian rhythms

► Shift work and jet lagShift work and jet lag When people abruptly change their daily rhythms of activity, their When people abruptly change their daily rhythms of activity, their

internal circadian rhythms become desynchronized with those in internal circadian rhythms become desynchronized with those in the external env’tthe external env’t

E.g. jet lagE.g. jet lag