Chapter 9- Sleep and Biological Rhythms
A physiological and behavioral description of sleep
Sleep is a behavior even if it is not distinguish by movement.
The change of consciousness is undeniable, but it should not prevent us from
noticing the behavioral changes.
Stages of sleep:
Research on human sleep is conducted in a sleep laboratory where the
experimenter attach electrodes to:
- the scalp of the sleeper to monitor the electroencephalogram (EEG)
- the chin of the sleeper to monitor muscle activity recorded as electromyogram
- around the eyes of the sleeper to monitor the eyes movements recorded as the
- measures heart rate, respiration and changes in the ability of the kin to conduct
During wakefulness EEG shows:
1. Alpha activity
- Smooth, regular, medium frequency waves (8-12 Hz)
- When a person is resting quietly, relaxed. Not particularly aroused, excited or
engaged in strenuous mental activity.
- Much more prevalent when the eyes are closed but can occur when eyes are open.
2. Beta activity
- Irregular, low-amplitude waves (13-30 Hz)
- Shows desynchrony: when many different neural circuits in the brain are actively
processing information. Occurs when a person is alert and attentive to events in the
environment or is thinking actively. (State of arousal)
During the experimentation:
Experimenter turns the light off and closes the door.
1. The subject becomes drowsy and enters stage 1 sleep
- Presence of theta activity (3.5-7.5 Hz) that indicates that the firing of neurons in
the neocortex is becoming more synchronized.
- Transition between sleep and wakefulness
- Eyelids slowly open and close and eyes roll upward and downward 2. 10 minutes later, the subjects enters in stage 2 sleep
- EEG is irregular but contains periods of theta activity
sleep spindles: short bursts of waves of 12-14 Hz that occur between two and five
times a minute during stage 1-4 of sleep
K complexes: sudden, sharp, waveforms, usually found only during stage 2 sleep.
Occur one time per minute but often can be triggered by noises, it's an inhibitory
mechanism that protects the sleeper from awakening. Appear during delta waves,
the deepest levels of sleep.
The subject sleep now but if awakened might report that he has not been asleep.
3. 15 minutes later, the subject enters in stage 3 sleep
- High-amplitude delta activity (less than 3.5 Hz): contains about 20-50 % delta
- Stage known as slow-wave sleep that occurs during the first half of the night
4. Subject enters stage 4 sleep
- Contains more than 50 % delta activity
- Stage known as slow-wave sleep that occurs during the first half on the night.
- Deepest stage of sleep; only loud noises can wake the person up and when waken
up he acts groggy and confused.
During slow-wave sleep:
Non- REM sleep; synchronized EEG activity during its deepest stages of slow-wave
Down state = period of inhibition; neurons in neocortex are silent and resting
Up state = period of excitation; neurons in neocortex fire briefly at high rate
those slow oscillations are synchronized with K complexes, sleep spindles and
delta waves. Those are important in learning and memory.
Change in the physiological measures of the subject, 90 min after the beginning of
sleep and 45 min after the onset of stage 4:
- EEG becomes desynchronized with a sprinkling of theta waves (similar to the stage
- Eyes are darting back and forth beneath her closed eyelids. The cornea produces a
bulge in the closed eyelids.
- EMG becomes silent = loss of muscle tone = A person become paralyzed during
REM sleep (Rapid Eye Movements)
- The person may not react to noises but he’s aroused by meaningful stimuli like the
sound of his name. When awaken, the person appear alert and attentive.
- The person is dreaming.
During the rest of the night the subject sleep will alternate between periods of REM
sleep and non-REM sleep (all stages of sleep except REM sleep). About REM sleep:
- A period of slow-wave sleep must precede REM sleep.
- The fact that REM sleep occurs at regular 90 min intervals suggests that a brain
mechanism alternately causes REM and slow-wave sleep.
- The cyclical nature of REM sleep is controlled by a “clock” in the brain that also
controls an activity cycle that continues through waking.
- We become paralyzed, most of our spinal and cranial motor neurons are inhibited
but at the same time the brain is very active: cerebral blood flow and oxygen
consumption are accelerated.
- A male’s penis can become erect and female’s vaginal secretions increase. (not due
to sexual arousal)
REM SLEEP SLOW-WAVE SLEEP
EEG desynchrony (rapid, irregular EEG synchrony (slow waves)
Lack of muscle tonus (paralyzed) Moderate muscle tonus
Rapid eye movements Slow or absent eye movements
Penile erection or vaginal secretion Lack of genital activity
Dreams (narrative, storylike)
Mental activity during sleep:
It is incorrect to refer sleep as a state of unconsciousness. It differs from waking
consciousness but we are conscious.
Rate of cerebral flood during REM is
- High in visual association cortex because of the visual hallucinations that occur
- Low in primary visual cortex because the eyes are not receiving visual input
- Low in prefrontal cortex (making plans, keeping track of the organization of events
in time, distinguish illusions from reality) because drams are poorly organized with
respect of time.
Eye movements made during REM sleep are related to the visual imagery occurring
while we dream. Researchers found that they were similar to what a subject would
have actually been watching these events.
Particular brain mechanisms that become active during a dream are those that
would be active if the events in the dreams were actually occurring.
Ex. Cortical and subcortical motor mechanisms become active during a dream that
Mental activity REM sleep during the dreams but it can also accompany slow-wave
sleep during the nightmares (especially stage 4 sleep). Disorders of sleep
- The amount of sleep that individuals require is variable.
- Insomnia must be defined in relation to a person’s particular sleep needs.
- The sleep of people who complain of insomnia and the sleep of people who did not
is actually the same, however there are personality difference, which could account
for the complaints.
- The evaluation of a sleeping medication must be made during wakefulness the
following day and must be “hangover-free”.
- Sleep apnea is a form of insomnia and is caused by an inability to sleep and breathe
at the same time. Patients fall asleep and cease to breathe.
- The level of carbon dioxide in the blood stimulates chemoreceptors (neurons that
detect the presence of certain chemicals) and the person wake up gasping for air,
then the level of oxygen returns to normal, the person fall asleep and the whole
cycle begins again.
- The period of anoxia during sleep apnea may damage neurons that play an
important role in wakefulness and alertness.
Neurological disorder characterize by sleep at inappropriate times.
- Sleep attack irresistible urge to sleep during the day that can happen at any
time, after which a person awakens feeling refreshed. (last 2-5 min)
-Cataplexy complete paralysis that occur during waking. The person will lie there
fully conscious for a few seconds to several minutes. One of the phenomena of REM
sleep- muscular paralysis – occurs at an inappropriate time. This is caused by a
massive inhibition of motor neurons in spinal cord. The person will loose control of
his muscles.Usually precipated by strong emotions reactions (especially when
caught unaware) or by sudden physical effort. (laughter, anger or effort to catch an
object can trigger cataplectic attack)
- Sleep paralysis REM sleep paralysis intrude into waking. Inability to move just
before the onset of sleep or upon waking in the morning. A person can be snapped
back out of sleep paralysis just by being touch or hearing his name. Components of
REM sleep intrude by dreaming while lying awake: this is called hypnagogic
hallucinations that are alarming and terrifying.
Narcolepsy is cause by a brain abnormality that disrupts the neural mechanisms
that control various aspects of sleep and arousal.
Orexin: a peptide, also known as hyprocretin, produced by neurons whose cell
bodies are located in the hypothalamus; their destructions causes narcolepsy. Its an hereditary disorder that can be treated with drugs.
REM Sleep Behavior Disorder:
Neurological disorder in which the person does not become paralyzed during REM
sleep and thus acts out dreams.
Appears to be a neurodegenerative disorder with some genetic component.
Associated with better-know neurodegenerative disorders such as Parkinson and
multiple system atrophy.
REM sleep disorder can be cause by brain damage (neural circuits in brain stem)
Symptoms are opposite of those of cataplexy: Patients fail to exhibit paralysis during
Treated by clonazepam, a benzodiazepine.
Problems associated with Slow-Wave Sleep (especially during deepest stage 4)
- Bedwetting: can be treated by training methods such as having a special electronic
circuit ring a bell when the first few drops of urine are detected.
- Sleepwalking: The person is not acting out his dreams. When occur in adulthood it
appear to have a genetic component. People can engage in complex behaviors.
- Sleep-related eating disorder: a person leaves his bed and seeks out and eats food
while sleepwalking without a memory of it the next day.
- Night terrors: Screams, trembling, rapid pulse and no memory of what caused the
terror. Cure when the child gets older.
Behaviors occur most frequently in children and are not related to REM sleep.
Why do we sleep?
Because sleep serves as an adaptative response or because it provides a period of
The fact that all vertebrates sleep, including some that would be better without it
suggests that sleep is more than an adaptative response.
Functions of Slow-Wave Sleep
The two hemispheres in dolphins sleep independently so that the animal can
remains behaviorally alert.
Effects of sleep deprivation
Studies with humans in sleep deprivation:
Show the primary role of sleep doesn’t seem to be rest and recuperation of the body.
However people’s cognitive abilities were affected and people can report perceptual
hallucinations and trouble concentrating in mental tasks. So sleep provides
opportunity for the brain to rest. Both cerebral metabolic rate and cerebral blood flow decline during slow-wave
Regions that have the highest levels of activity during waking shows the highest
levels of delta waves and the lowest waves of metabolic activity.
During stage 4, the brain is resting.
Prolonged sleep-deprivation caused an increase in free radicals in the brain of rats
and caused oxidative stress (when radicals which are highly reactive oxidizing
agents, can bind with electrons of other molecules and damage the cells in which
they are found.)
During slow-wave sleep the lowered rate of metabolism permits restorative
mechanisms in the cells to destroy the free radicals and prevent their damaging
Fatal familial insomnia:
- Fatal inherited disorder characterized by progressive insomnia.
- Occur when damage to portions of the thalamus.
- Includes deficit in attention and memory followed by a dreamlike, confused state,
loss of control of the autonomic nervous and endocrine system; increased body
temperature and insomnia.
First signs = reductions in sleep spindles and K complexes, then slow-wave sleep
completely disappears and only brief episodes of REM sleep remain.
Studies with laboratory animal in sleep deprivation:
Serious effects: animals looked sick and stopped grooming their fur. They became
weak, uncoordinated and loss their ability to regulate their body temperature.
Although they began eating much more food than normal, their metabolic system
became so high that they continued losing weight.
Eventually the rats died but the cause of death is still not understood.
Effects of exercise on Slow-Waves Sleep
Brain needs slow-wave sleep in order to recover from the day’s activities but
changes in a person’s level of exercise do not significantly alter the amount of sleep
the person needs the following night.
Effects of brain activity on Slow-Wave Sleep
Tasks that demand alertness and mental activity do increase glucose metabolism in
the brain. The most significant increases is seen in the frontal lobes where slow-
wave activity is most intense during non-REM sleep.
During sleep the subjects showed increased slow-wave activity in the region of the
neocortex that become active while performing the task. The increased activity of
these cortical neurons called for more rest during the following night’s sleep.
Functions of REM sleep
Time of intense physiological activity: eyes dart rapidly, heart rate shows
accelerations/decelerations, breathing is irregular, brain becomes more active.
Rebound phenomenon: the increased frequency or intensity of a phenomenon after it has been temporarily suppressed; for example the increase in REM sleep seen
after a period of REM sleep deprivation.
Function of REM sleep is to promote brain development and to facilitate learning.
Sleep and learning
Sleep aids consolidation of long-term memories.
Slow-wave sleep and REM sleep play different roles in the consolidation of
declarative (explicit memory) and nondeclarative memories (implicit memory).
REM sleep is associated with nondeclarative memories and Slow-Wave sleep with
Physiological mechanisms of sleep and waking
Chemical controls of sleep
- Some physiological mechanism monitors the amount of sleep that an organism
- The body produces a sleep-promoting substance during that accumulates during
wakefulness and is destroyed during sleep. The longer someone is awake the longer
he had to sleep to deactivate this substance.
- There might be 2 substances, one for each stage of sleep.
- Sleep is control by chemicals in the blood:
- Adenosine a neuromodulator that is released by neurons engaging in high levels
of metabolic activity, play a primary role in the initiation of sleep.
- A fall in the level of glycogen causes an increase in the level of extracellular
adenosine, which have an inhibitory effect on neural activity, This accumulation of
adenosine serves as a sleep-promoting substance.
- During slow-wave sleep, neurons in the brain rest and stock of glycogen is
renewed, but if wakefulness is prolonged, more adenosine accumulates creates the
cognitive and emotional effects that are seen during sleep deprivation.
Neural control of arousal
Circuits of neurons that secrete different neurotransmitters play a role in aspect of
an animal’s level of arousal.
- one of the most important (especially of the cerebral cortex)
- 2 groups of neurons (one in the pons and the other in basal forebrain) produce
activation and cortical desynchrony when they are stimulated. A third group located