Biological Psychology, 5e

14Biological Rhythms,Sleep, and Dreaming

14 Biological Rhythms, Sleep, and Dreaming

Biological Rhythms

• Many Animals Show Daily Rhythms in Activity

• The Hypothalamus Houses an Endogenous Circadian Clock

• Animals Use Circannual Rhythms to Anticipate Seasonal Changes


Sleeping and Waking

• Human Sleep Exhibits Different Stages

• The Sleep of Different Species Provides Clues about the Evolution of Sleep

• Our Sleep Patterns Change across the Life Span

• Manipulating Sleep Reveals an Underlying Structure


• What are the Biological Functions of Sleep?

• At Least Four Interacting Neural Systems Underlie Sleep

• Sleep Disorders Can Be Serious, Even Life-Threatening

Many Animals Show Daily Rhythms in Activity

Circadian rhythms are those functions of a living organism that display a rhythm of about 24 hours.

Rhythms may be behavioral, physiological, or biochemical.

Diurnal—active during the light

Nocturnal—active during the dark

Figure 14.1 How Activity Rhythms are Measured (Part 1)


Circadian rhythms are generated by an endogenous (internal) clock.

A free-running animal is maintaining its own cycle with no external cues, such as light.

The period, or time between successive cycles, may not be exactly 24 hours.

Figure 14.1 How Activity Rhythms are Measured (Part 2)


A phase shift is the shift in activity in response to a synchronizing stimulus, such as light or food.

Entrainment is the process of shifting the rhythm.

The cue that an animal uses to synchronize with the environment is called a zeitgeber—“time-giver”

The Hypothalamus Houses an Endogenous Circadian Clock

The biological clock is in the suprachiasmatic nucleus (SCN)—located above the optic chiasm in the hypothalamus.

Studies showed that circadian rhythms were disrupted in SCN-lesioned animals.

Isolated SCNs can maintain electrical activity synchronized to the previous light cycle.

Figure 14.2 The Effects of Lesions in the SCN

Figure 14.3 The Circadian Rhythm of Metabolic Activity of the SCN


Transplant studies proved that the endogenous period is generated in the SCN.

Hamsters with abolished circadian rhythms received an SCN tissue transplant from hamsters with a very short period, ~20 hours.

The rhythms were restored but matched the shorter period of the donor.

Figure 14.4 Brain Transplants Prove that the SCN Contains a Clock


Circadian rhythms entrain to light–dark cycles using different pathways, some outside of the eye.

In amphibians and birds, the pineal gland is sensitive to light.

In mammals, light information goes from the eye to the SCN via the retinohypothalamic pathway.


The retinohypothalamic pathway consists of retinal ganglion cells that project to the SCN.

These ganglion cells do not rely on rods and cones.

Most of these retinal ganglion cells contain melanopsin, a special photopigment, that makes them sensitive to light.

Figure 14.5 The Retinohypothalamic Pathway in Mammals

Figure 14.6 Schematic Showing the Components of a Circadian System


Molecular studies in Drosophila using mutations of the period gene helped to understand the circadian clock in mammals.

SCN cells in mammals make two proteins:

• Clock

• Cycle


Clock and Cycle proteins bind together to form a dimer.

The Clock/Cycle dimer promotes transcription of two genes:

• Period (per)

• Cryptochrome (cry)


Proteins arising from per and cry bind to each other and to a third one, Tau.

The Per/Cry/Tau protein complex enters the nucleus and inhibits the transcription of per and cry.

No new proteins are made, until the first set degrades and the cycle begins again every ~24 hours.

Figure 14.7 A Molecular Clock in Flies and Mice


Light entrains the molecular clock in different ways.

In flies, light reaches the brain directly and degrades a clock protein.

In mammals, melanopsin cells detect light and release glutamate in the SCN.

Glutamate triggers events that promote production of the Per protein, which in turn shifts the clock and the animal’s behavior.


Gene mutations show how important the clock is to behavior in constant conditions:

tau mutations—the period is shorter than normal

Double Clock mutants—arrhythmic

Single Clock mutants—period is longer than normal

Figure 14.8 When the Endogenous Clock Goes Kaput


Some biological rhythms are shorter, such as bouts of activity, feeding, and hormone release.

These ultradian rhythms occur more than once per day.

Period length can be from minutes to hours.

Animals Use Circannual Rhythms to Anticipate Seasonal Changes

Other biological rhythms are long, such as body weight, and reproductive cycles.

An endogenous circannual clock, separate from the SCN, runs at ~365 days.

Infradian rhythms occur less than once per day.

Figure 14.9 A Hamster for All Seasons

Sleeping and Waking

Sleep is synchronized to external events, including light and dark.

Stimuli like lights, food, 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.

Figure 14.10 Humans Free-Run Too

Figure 14.11 Oh, How I Hate to Get Out of Bed in the Morning

Human Sleep Exhibits Different Stages

Electrical brain potentials can be used to classify levels of arousal and states of sleep.

Electroencephalography (EEG)—records electrical activity in the brain

Electro-oculography (EOG)—records eye movements

Electromyography (EMG)—records muscle activity


Two distinct classes of sleep:

Slow-wave sleep (SWS)—can be divided into four stages and is characterized by slow-wave EEG activity

Rapid-eye-movement sleep (REM)—characterized by small amplitude, fast-EEG waves, no postural tension, and rapid eye movements


The pattern of activity in an awake person contains many frequencies:

• Dominated by waves of fast frequency and low amplitude (15 to 20 Hz).

• Known as beta activity or desynchronized EEG

Alpha rhythm—occurs in relaxation, a regular oscillation of 8 to 12 Hz


Four stages of slow-wave sleep:

Stage 1 sleep—shows events of irregular frequency and smaller amplitude, as well as vertex spikes, or sharp waves

• Heart rate slows, muscle tension reduces, eyes move about

• Lasts several minutes


Stage 2 sleep:

• Defined by waves of 12 to 14 Hz that occur in bursts, called sleep spindles

• K complexes appear—sharp negative EEG potentials


Stage 3 sleep:

• Continued sleep spindles as in stage 2

• Defined by the appearance of large-amplitude, very slow waves called delta waves

• Delta waves occur about once per second


Stage 4 sleep:

• Delta waves are present about half the time

REM sleep follows:

• Active EEG with small-amplitude, high-frequency waves, like an awake person

• Muscles are relaxed—called paradoxical sleep

Figure 14.12 Electrophysiological Correlates of Sleep and Waking


In a typical night of young adult sleep:

• Sleep time ranges from 7-8 hours.

• 45-50% is stage 2 sleep, 20% is REM sleep.

• 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.

Figure 14.13 A Typical Night of Sleep in a Young Adult


Vivid dreams occur during 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.

Figure 14.14 Night Terror

The Sleep of Different Species Provides Clues about the Evolution of Sleep

REM sleep evolved in some vertebrates:

• Nearly all mammals display both REM and SWS, except the echidna—a monotreme, or egg-laying mammal—that may not have REM sleep

• Birds also display both REM and SWS sleep

Figure 14.15 Amounts of Different Sleep States in Various Mammals


Marine mammals do not show REM sleep, perhaps because relaxed muscles are incompatible with the 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.

Figure 14.16 Sleep in Marine Mammals


A sleep cycle is a period of SWS followed by one of REM sleep.

Most vertebrates show:

• A circadian distribution of activity

• A prolonged phase of inactivity Raised thresholds to external stimuli Characteristic posture

Our Sleep Patterns Change across the Life Span

Mammals sleep more during infancy than in adulthood.

Infant sleep is characterized by:

• Shorter sleep cycles

• More REM sleep—50%, which may provide essential stimulation to the developing nervous system

Figure 14.17 The Trouble with Babies

Figure 14.18 Human Sleep Patterns Change with Age

Our Sleep Patterns Change across the Life Span

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:

• At age 60 only half as much time is spent as at age 20—by age 90 stages 3 and 4 have disappeared.

Figure 14.19 The Typical Pattern of Sleep in an Elderly Person

Manipulating Sleep Reveals an Underlying Structure

Effects of sleep deprivation—the partial or total prevention of sleep:

• Increased irritability

• Difficulty in concentrating

• Episodes of disorientation

Effects can vary with age and other factors.

Figure 14.20 I Need Sleep!


Total sleep deprivation compromises the immune system and leads to death.

The disease fatal familial insomnia is inherited—in midlife people stop sleeping and die 7-24 months after onset of the insomnia.


Sleep recovery is the process of sleeping more than normally, after a period of deprivation.

Night 1—stage 4 sleep is increased, but stage 2 is decreased

Night 2—most recovery of REM sleep, which is more intense than normal with more rapid eye movements

Figure 14.21 Sleep Recovery after 11 Days Awake

What Are the Biological Functions of Sleep?

Four functions of sleep:

1. Energy conservation

2. Predator avoidance

3. Body restoration

4. Memory consolidation


Energy is conserved during sleep: muscular tension, heart rate, blood pressure, temperature and rate of respiration are reduced

Small animals sleep more than large ones, in correlation with their high normal metabolic rate.

Figure 14.22 Sleep Helps Animals to Adapt an Ecological Niche


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, such as proteins. Growth hormone is only released during SWS.


Explanations for memory consolidation and learning vary from passive to active:

• Sleep during the interval between learning and recall may reduce interfering stimuli.

• Memory typically decays and sleep may slow this down.

• Or, sleep, especially REM, may actively contribute through processes that consolidate the learned material.

Figure 14.23 A Nonsleeper

At Least Four Interacting Neural Systems Underlie Sleep

Sleep is an active state mediated by:

1. A forebrain system, displays SWS

2. A brainstem system, activates the forebrain

3. A pontine system, triggers REM sleep

4. A hypothalamic system, affects the other three


Transection experiments showed that different sleep systems originate in different parts of the brain.

Encéphale isolé, or isolated brain, is made by an incision between the medulla and the spinal cord.

Animals showed signs of sleep and wakefulness, proving that the networks reside in the brain.


Cerveau isolé, or isolated forebrain, is made by an incision in the midbrain.

The electrical activity in the forebrain showed constant SWS, but not REM—thus the forebrain alone can generate SWS.

Figure 14.24 Brain Transections Reveal Sleep Mechanisms


The constant SWS activity in the forebrain is generated by the basal forebrain.

Neurons in this region become active at sleep onset and release GABA.

GABA suppresses activity in the nearby tuberomamillary nucleus.


Reduced activity in the tuberomamillary nucleus suppresses wakefulness.

General anesthetics make GABAA receptors in the tuberomamillary nucleus more sensitive to GABA and induce a SWS state.


The reticular formation is able to activate the cortex.

Electrical stimulation of this area will wake up sleeping animals while lesions of this area promote sleep.

The forebrain and reticular formation seem to guide the brain between SWS and wakefulness.


An area of the pons, near the locus coeruleus, is responsible for REM sleep.

Some neurons in this region are only active during REM sleep.

They inhibit motoneurons to keep them from firing, disabling the motor system during REM sleep.

Figure 14.25 The Brainstem Reticular Formation

Figure 14.26 Sleep Stage Postures


The study of narcolepsy revealed the hypothalamic sleep center.

Narcolepsy sufferers:

• Have frequent sleep attacks and excessive daytime sleepiness

• Do not go through SWS before REM sleep

• May show cataplexy—a sudden loss of muscle tone, leading to collapse


Narcoleptic dogs have a mutant gene for a hypocretin receptor.

Hypocretin normally prevents the transition from wakefulness directly into REM sleep.

Interfering with hypocretin signaling leads to narcolepsy.

Figure 14.27 Narcolepsy in Dogs


Hypocretin neurons in the hypothalamus project to other brain centers: the basal forebrain, the reticular formation and the locus coeruleus.

Axons also go to the tuberomamillary nucleus, whose inhibition induces SWS.

The hypothalamic hypocretin sleep center may act as a switch, controlling wakefulness, SWS sleep or REM sleep.

Figure 14.28 Neural Degeneration in Humans with Narcolepsy


Sleep paralysis is the brief inability to move just before falling asleep, or just after waking up.

It may be caused by the pontine center continuing to signal for muscle relaxation, even when awake.

Sleep Disorders Can Be Serious, Even Life-Threatening

Sleep disorders in children:

Night terrors and sleep enuresis (bed-wetting) are associated with SWS.

Somnambulism (sleepwalking) occurs during stages 3 and 4 SWS, and may persist into adulthood.


REM behavior disorder (RBD) is characterized by organized behavior from an asleep person.

It usually begins after age 50 and may be followed by beginning symptoms of Parkinson’s disease.

This suggests damage in the brain motor systems.


Sleep state misperception occurs when people report insomnia even when they were asleep.

Sleep-onset insomnia is a difficulty in falling asleep, and can be caused by situational factors, such as shift work or jet lag.

Sleep-maintenance insomnia is a difficulty in staying asleep and may be caused by drugs or neurological factors.


In sleep apnea, breathing may stop or slow down—blood oxygen drops rapidly.

Muscles in the chest and diaphragm may relax too much or pacemaker respiratory neurons in the brain stem may not signal properly.

Sleep apnea may be accompanied by snoring.


Each episode of sleep apnea arouses the person to restore breathing, but may result in daytime sleepiness.

Treatments include a removable tube in the throat or a CPAP (continuous positive airway pressure) machine, to prevent collapse of the airways.

Figure 14.29 A Machine That Prevents Sleep Apnea


Untreated sleep apnea can lead to cardiovascular disorders.

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.

Figure 14.30 Back to Sleep


Sleeping pills are not perfect—most bind to GABA receptors throughout the brain. Continued use of sleeping pills:

• Makes them ineffective

• Produces marked changes in sleep patterns that persist even when not taking the drug

• Can lead to drowsiness and memory gaps

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Biological Psychology, 5e