Neural Basis of Behavior: Sleep
Department of Rehabilitation Medicine
Rhythms of Waking and Sleep
•Animals generate endogenous 24 hour cycles of wakefulness
and sleep.
•Some animals generate endogenous circannual rhythms, internal
mechanisms that operate on an annual or yearly cycle.
–Prepares animals e.g. birds for seasonal changes
Rhythms of Waking and Sleep
 All animals produce endogenous circadian rhythms, internal
mechanisms that operate on an approximately 24 hour cycle.
–Regulates the sleep/ wake cycle.
–Also regulates the frequency of eating and drinking, body
temperature, secretion of hormones, volume of urination, and
sensitivity to drugs.
Rhythms of Waking and Sleep
Circadian rhythms:
•Remains consistent despite lack of environmental cues
indicating the time of day
•Can differ between people and lead to different patterns of
wakefulness and alertness.
•Change as a function of age.
–Example: sleep patterns from childhood to late adulthood.
Rhythms of Waking and Sleep
•The duration of the rhythm depends on the amount of light
•Experiments designed to determine the length of the circadian
rhythm place subjects in environments with no cues to time of
day.
•Results depend upon the amount of light to which subjects are
artificially exposed.
–Rhythms run faster in bright light conditions and subjects have
trouble sleeping.
–In constant darkness, people have difficulty waking.
Rhythms of Waking and Sleep
•Biological clock – the brain generates its own rhythm
•Human circadian clock generates a rhythm slightly longer than
24 hours when it has no external cue to set it.
•Most people can adjust to 23- or 25- hour day but not to a 22- or
28- hour day.
•Bright light late in the day can lengthen the circadian rhythm.
Rhythms of Waking and Sleep
•Mechanisms of the circadian rhythms include the following:
–The Suprachiasmatic nucleus.
–Genes that produce certain proteins.
–Melatonin levels.
Rhythms of Waking and Sleep
•The suprachiasmatic nucleus (SCN) is part of the hypothalamus
and the main control center of the circadian rhythms of sleep
and temperature.
–Located above the optic chiasm.
–Damage to the SCN results in less consistent body rhythms
that are no longer synchronized to environmental patterns of
light and dark.
Rhythms of Waking and Sleep
•The SCN regulates waking and sleeping by controlling activity
levels in other areas of the brain.
•The SCN regulates the pineal gland, an endocrine gland located
posterior to the thalamus.
•The pineal gland secretes melatonin, a hormone that increases
sleepiness.
Rhythms of Waking and Sleep
•Melatonin secretion usually begins 2 to 3 hours before bedtime.
•Melatonin feeds back to reset the biological clock through its
effects on receptors in the SCN.
•Melatonin taken in the afternoon can phase-advance the internal
clock and can be used as a sleep aid.
Rhythms of Waking and Sleep
•The purpose of the circadian rhythm is to keep our internal
workings in phase with the outside world.
•Light is critical for periodically resetting our circadian rhythms.
•A zeitgeber is a term used to describe any stimulus that resets
the circadian rhythms.
•Exercise, noise, meals, and temperature are others zeitgebers.
Rhythms of Waking and Sleep
•Light resets the SCN via a small branch of the optic nerve known
as the retinohypothalamic path.
–Travels directly from the retina to the SCN.
•The retinohypothalamic path comes from a special population of
ganglion cells that have their own photopigment called
melanopsin.
–The cells respond directly to light and do not require any input
from the rods or cones.
Rhythms of Waking and Sleep
•Jet lag refers to the disruption of the circadian rhythms due to
crossing time zones.
–Stems from a mismatch of the internal circadian clock and
external time.
•Characterized by sleepiness during the day, sleeplessness at
night, and impaired concentration.
•Traveling west “phase-delays” our circadian rhythms.
•Traveling east “phase-advances” our circadian rhythms.
Stages of Sleep And Brain
Mechanisms
•The electroencephalograph (EEG) allowed researchers to
discover that there are various stages of sleep.
•Over the course of about 90 minutes:
– a sleeper goes through sleep stages 1, 2, 3, and 4
–then returns through the stages 3 and 2 to a stage called REM.
Stages of Sleep And Brain
Mechanisms
•Alpha waves are present when one begins a state of relaxation.
•Stage 1 sleep is when sleep has just begun.
–the EEG is dominated by irregular, jagged, low voltage waves.
–brain activity begins to decline.
Stages of Sleep And Brain
Mechanisms
Stages of Sleep And Brain
Mechanisms
•Stage 2 sleep is characterized by the presence of:
–Sleep spindles - 12- to 14-Hz waves during a burst that lasts at
least half a second.
–K-complexes - a sharp high-amplitude negative wave followed
by a smaller, slower positive wave.
Stages of Sleep And Brain
Mechanisms
Stages of Sleep And Brain
Mechanisms
•Stage 3 and stage 4 together constitute slow wave sleep (SWS)
and is characterized by:
–EEG recording of slow, large amplitude wave.
–Slowing of heart rate, breathing rate, and brain activity.
Stages of Sleep And Brain
Mechanisms
Stages of Sleep And Brain
Mechanisms
•Rapid eye movement sleep (REM) are periods characterized by
rapid eye movements.
•EEG waves are irregular, low-voltage and fast.
•Postural muscles of the body are more relaxed than other stages.
•Strongly associated with dreaming, but people also report
dreaming in other stages of sleep.
•Also known as “paradoxical sleep” because it is deep sleep in
some ways, but light sleep in other ways.
Stages of Sleep And Brain Mechanisms
Stages of Sleep And Brain
Mechanisms
•Stages other than REM are referred to as non-REM sleep (NREM).
•When one falls asleep, they progress through stages 1, 2, 3, and
4 in sequential order.
•After about an hour, the person begins to cycle back through the
stages from stage 4 to stages 3 and 2 and than REM.
•The sequence repeats with each cycle lasting approximately 90
minutes.
Stages of Sleep And Brain
Mechanisms
•Stage 3 and 4 sleep predominate early in the night.
–The length of stages 3 and 4 decrease as the night progresses.
•REM sleep is predominant later in the night.
–Length of the REM stages increases as the night progresses.
Stages of Sleep And Brain
Mechanisms
•Various brain mechanisms are associated with wakefulness and
arousal.
•The reticular formation is a part of the midbrain that extends from
the medulla to the forebrain and is responsible for arousal.
Stages of Sleep And Brain
Mechanisms
•The hypothalamus contains neurons that release “histamine” to
produce widespread excitatory effects throughout the brain.
–Anti-histamines produce sleepiness.
•Orexin is a peptide neurotransmitter released in a pathway from
the lateral nucleus of the hypothalamus highly responsible for
the ability to stay awake.
–Stimulates acetylcholine-releasing cells in the forebrain and
brain stem to increase wakefulness and arousal.
Stages of Sleep And Brain
Mechanisms
•During REM sleep:
–Activity increases in the pons triggers the onset of REM sleep,
evident by the presence of pons-geniculate-occipital (PGO)
waves
–Activity decreases in the primary visual cortex, the motor
cortex, and the prefrontal cortex.
Stages of Sleep And Brain
Mechanisms
•Cells in the pons send messages to the spinal cord which inhibit
motor neurons that control the body’s large muscles.
•Prevents motor movement during REM sleep.
•Input from the pons activates the amygdala giving the dream an
emotional content.
•Because much of the prefrontal cortex is inactive, memory of
dreams is weak.
–Also explains sudden scene changes that during occur in
dreams.
Stages of Sleep And Brain
Mechanisms
•Decreased arousal required for sleep is accomplished via the
following ways:
1.Decrease of body temperature
2.Decrease of external stimulation
3.Increase of adenosine in the brain to inhibit the basal
forebrain cells responsible for arousal. (Caffeine blocks
adenosine receptors)
4.Accumulation of prostaglandins that inhibit the hypothalamic
cells responsible for increased arousal. (The immune system
increase its concentration in response to infection)
Stages of Sleep And Brain
Mechanisms
•Abnormalities of sleep
–Insomnia: a sleep disorder associated with inability to fall
asleep or stay asleep.
–Related to abnormality of biological rhythms.
–Onset insomnia
–Maintenance insomnia
–Termination insomnia
Stages of Sleep And Brain
Mechanisms
•Sleep apnea: inability to breathe while sleeping for a prolonged
period of time.
•Narcolepsy: frequent periods of sleepiness.
–Symptoms: sudden sleepiness; cataplexy; sleep paralysis;
hypnagogic hallucination
•Night terrors: experiences of intense anxiety usually occurs in
NREM sleep.
•Sleep talking: occurs in both REM and NREM sleep.
•Sleepwalking: occurs mostly in stage 3 or 4 sleep. (Does not
occur in REM sleep)
Why Sleep? Why REM? Why Dreams?
•Sleep is a specialized state that serves a variety of important
functions including:
–conservation of energy
–repair and restoration
–learning and memory consolidation
•Animals sleep habits and are influenced by particular aspects of
their life.
•Some animals also increase their sleep time during food
shortages.
–sleep is analogous to the hibernation of animals.
Why Sleep? Why REM? Why Dreams?
•People vary in their need for sleep.
–Most sleep about 8 hours.
•Sleep enables restorative processes in the brain to occur.
–Proteins are rebuilt.
–Energy supplies are replenished.
•Sleep also plays an important role in enhancing learning and
strengthening memory.
Why Sleep? Why REM? Why Dreams?
•Research is inconclusive regarding the exact functions of REM.
•During REM:
–The brain may discard useless connections
–Learned motor skills may be consolidated.
Why Sleep? Why REM? Why Dreams?
•Biological perspectives of dreaming
•The activation-synthesis hypothesis suggests dreams begin with
spontaneous activity in the pons which activates many parts of
the cortex.
–The cortex synthesizes a story from the pattern of activation.
•The clinico-anatomical hypothesis places less emphasis on the
pons, PGO waves, or even REM sleep.
–Suggests that dreams are similar to thinking, just under
unusual circumstances.