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Three Standard Psychophysiological Measures of Sleep

  • sleep lab

  • go to peoples home

  • measure electrical brain activity via EEG (electroencephalogram)

  • measure eye movement during sleep via EOG (electrooculogram)

  • measure muscle activity (chin or legs) - useful identifying sleep disorder via EMG (electromyogram)


The three stages of the sleep EEG,

There are two basic types of sleep:  rapid eye movement (REM) sleep and non-REM sleep (which has three different stages).  Each is linked to specific brain waves and neuronal activity.  You cycle through all stages of non-REM and REM sleep several times during a typical night, with increasingly longer, deeper REM periods occurring toward morning. 

Stage 1 non-REM sleep is the changeover from wakefulness to sleep.  During this short period (lasting several minutes) of relatively light sleep, your heartbeat, breathing, and eye movements slow, and your muscles relax with occasional twitches.  Your brain waves begin to slow from their daytime wakefulness patterns. 

Stage 2 non-REM sleep is a period of light sleep before you enter deeper sleep.  Your heartbeat and breathing slow, and muscles relax even further.  Your body temperature drops and eye movements stop.  Brain wave activity slows but is marked by brief bursts of electrical activity.  You spend more of your repeated sleep cycles in stage 2 sleep than in other sleep stages.

Stage 3 non-REM sleep is the period of deep sleep that you need to feel refreshed in the morning.  It occurs in longer periods during the first half of the night.  Your heartbeat and breathing slow to their lowest levels during sleep.  Your muscles are relaxed and it may be difficult to awaken you.  Brain waves become even slower. 

REM sleep first occurs about 90 minutes after falling asleep.  Your eyes move rapidly from side to side behind closed eyelids.  Mixed frequency brain wave activity becomes closer to that seen in wakefulness.  Your breathing becomes faster and irregular, and your heart rate and blood pressure increase to near waking levels.  Most of your dreaming occurs during REM sleep, although some can also occur in non-REM sleep.  Your arm and leg muscles become temporarily paralyzed, which prevents you from acting out your dreams.  As you age, you sleep less of your time in REM sleep.  Memory consolidation most likely requires both non-REM and REM sleep.


Theories of Sleep

  • The essence of recuperation theories of sleep is that being awake disrupts the homeostasis (internal physiological stability) of the body in some way and sleep is required to restore it. 
  • We sleep to restore energy levels and clear toxins.


  • The essence of adaptation theories of sleep is that sleep is not a reaction to the disruptive effects of being awake but the result of an internal 24-hour timing mechanism—that is, we humans are programmed to sleep at night regardless of what happens to us during the day.


Comparative Analysis of Sleep

  1. Most mammals and birds sleep - which suggests a physiological function
  2. Is not just a higher-order human function.
  3. Essential for survival
  4. No strong relationship between a species sleep time and level of activity, body size or body temperature


Reasons for sleep deprivation

shift work = affects your sleep cycle and can lead to sleep deprivation
sleep disorders
lifestyle - 24/7 society: internet and mobile phones
family commitment - young children
anxiety - increases arousal
stimulants - hinder ability to get to sleep


three predictions that recuperation theories make about the effects of sleep deprivation

  • Long periods of wakefulness will produce physiologi-cal and behavioral disturbances.
  • These disturbances will grow worse as the sleep de-privation continues.
  • After a period of deprivation has ended, much of the missed sleep will be regained.


Signs of sleep deprivation

a whole range of physiological and psychological consequences
- difficulty making simple decisions
- difficulty concentrating
- falling asleep
- weak immune system
- feeling more emotional than usual
- still feeling hungry after eating


Consequences of sleep deprivation

- cognitive function
- emotional wellbeing
- weight management
- reproductive system --> affects testosterone and sperm quality
- immune system

- brain structure affected
- verbal disturbances
- impaired learning, poor decision making, mental fatigue (may be due to abnormal function of prefrontal cortex)

- 6-8% decrease in brain metabolic rate
- aching muscles
- headaches
- increase blood pressure
- increase risk of diabetes
- obesity
- seizures


Common themes in the definition of sleep

lack of consciousness/ temporary suspension of consciousness
naturally- occurring state
periodic and recurring
involves mind and body
relaxation and inactivity of muscles
--> sleep presents itself differently in different species, therefore, it is hard to find one definition that is applicable to all animals


Sleep Deprivation Increases the Efficiency of Sleep

  • Although people regain only a small proportion of their total lost sleep after a period of sleep depriva-tion, they regain most of their lost slow-wave sleep
  • After sleep deprivation, the slow-wave sleep EEG of humans is characterized by an even higher propor-tion of slow waves than usual
  • People who sleep 6 hours or less per night normally get as much slow-wave sleep as people who sleep 8 hours or more
  • If individuals take a nap in the morning after a full night’s sleep, their naptime EEG shows few slow waves, and the nap does not reduce the duration of the following night’s sleep
  • People who reduce their usual sleep time get less NREM 1 and NREM 2 sleep, but the duration of their slow-wave sleep remains about the same as before
  • Repeatedly waking individuals during REM sleep produces little increase in the sleepiness they ex-perience the next day, whereas repeatedly wakingindividuals during slow-wave sleep has major ef-fects


REM Sleep

Rapid eye movement sleep (REM sleep or REMS) is a unique phase of sleep in mammals and birds, characterized by random rapid movement of the eyes, accompanied by low muscle tone throughout the body, and the propensity of the sleeper to dream vividly.


Circadian Rhythm

a natural, internal process that regulates the sleep-wake cycle and repeats on each rotation of the Earth roughly every 24 hours. It can refer to any biological process that displays an endogenous, entrainable oscillation of about 24 hours.



a rhythmically occurring natural phenomenon which acts as a cue in the regulation of the body's circadian rhythms.


literally "time giver", i.e., "synchronizer"


Jet Lag and Shift Work

Traveling across time zones can disrupt regular patterns of sleep and wakefulness.

Because the internal circadian alerting system is at its strongest during the daytime, night shift workers often find themselves struggling to sleep "on the wrong side of the clock."

Good sleep habits (in particular), a regular schedule, and simple workplace measures can help shift workers get the sleep they need.

Symptoms of jet lag may include excessive daytime sleepiness, nighttime insomnia, headache, loss of appetite, gastrointestinal problems, and irritability or mild depression.


The suprachiasmatic nucleus or nuclei (SCN)

is a tiny region of the brain in the hypothalamus, situated directly above the optic chiasm. It is responsible for controlling circadian rhythms. The neuronal and hormonal activities it generates regulate many different body functions in a 24-hour cycle. The mouse SCN contains approximately 20,000 neurons.[1]

The SCN interacts with many other regions of the brain. It contains several cell types and several different peptides (including vasopressin and vasoactive intestinal peptide) and neurotransmitters.


Two regions of the brain involved in sleep.

The anterior hypothalamus and adjacent basal forebrain are thought to promote sleep;

the posterior hypothalamus and adjacent midbrain are thought to promote wakefulness.


reticular activating system

The reticular activating system (RAS) is a network of neurons located in the brain stem that project anteriorly to the hypothalamus to mediate behavior, as well as both posteriorly to the thalamus and directly to the cortex for activation of awake, desynchronized cortical EEG patterns.


Drugs That Affect Sleep

Hypnotic drugs are drugs that increase sleep;

antihypnotic drugs are drugs that reduce sleep.

A third class of sleep-influencing drugs comprises those that influence its circadian rhythmicity; the main drug of this class is melatonin.


Hypnotic Drugs

The benzodiazepines (e.g., diazepam, clonazepam), which are GABAA agonists, were developed and tested for the treat-ment of anxiety, yet they are some of the most commonly prescribed hypnotic medications. In the short term, they increase drowsiness, decrease the time it takes to fall asleep, reduce the number of awakenings during a night’s sleep, and increase total sleep time

In the early 1990s, a new class of GABAA agonists, the imidazopyridines, was marketed for the treatment of insomnia. It was claimed that they have fewer adverse side effects and less potential for addiction. One of the most widely prescribed imidazopyridines is Zolpidem

Evidence that the raphé nuclei, which are seroto-nergic, play a role in sleep suggested that serotonergic drugs might be effective hypnotics. Efforts to demon-strate the hypnotic effects of such drugs have focused on 5-hydroxytryptophan (5-Htp)—the precursor of sero-tonin—because 5-HTP, but not serotonin, readily passes through the blood–brain barrier. Injections of 5-HTP do reverse the insomnia produced in both cats and rats by the serotonin antagonist PCPA; however, they appear to be of no therapeutic benefit in the treatment of human insomnia.


Five complications are associated with the chronic use of benzodiazepines as hypnotic agents:

  • Tolerance develops to the hypnotic effects of benzo-diazepines; thus, patients must take larger and larger doses to maintain the drugs’ efficacy.
  • Cessation of benzodiazepine therapy after chronic use causes insomnia (sleeplessness), which can exacerbate the very problem that the benzodiazepines were in-tended to correct.
  • Benzodiazepines distort the normal pattern of sleep; they increase the duration of NREM 2 sleep while actually decreasing the duration of both slow-wave and REM sleep.
  • Benzodiazepines lead to next-day drowsiness and increase the incidence of traffic accidents
  • Most troubling is that chronic use of benzodiazepines has been shown to substantially reduce life expectancy


Antihypnotic Drugs

cocaine-derived stimulants, amphetamine-derived stimulants, and tricyclic antidepressants.

The drugs in these three classes seem to promote wakefulness by boosting the activity of catecholamines (norepinephrine, epinephrine, and dopamine)—by increasing their release into synapses, by blocking their reuptake from synapses, or both.

The regular use of antihypnotic drugs is risky. Antihypnotics tend to produce a variety of adverse side effects, such as loss of appetite, anxiety, tremor, addiction, and disturbance of normal sleep patterns. Moreover, they may mask the pathology that is causing the excessive sleepiness.



Melatonin is a hormone synthesized from the neurotrans-mitter serotonin in the pineal gland


ad-ministration of melatonin in the evening increases sleep by accelerating the start of the nocturnal phase of the circadian rhythm and that administration at dawn increases sleep by delaying the end of the nocturnal phase.


Sleep Disorders

insomnia includes all disorders of initiating and maintaining sleep

Hypersomnia includes disorders of excessive sleep or sleepiness

A third major class of sleep disorders includes all those dis-orders that are specifically related to REM-sleep dysfunc-tion

Both insomnia and hypersomnia are common symptoms of depression and bipolar disorders



  • also called a sleep study, is a test used to diagnose sleep disorders. Polysomnography records your brain waves, the oxygen level in your blood, heart rate and breathing, as well as eye and leg movements during the study.
  • Your doctor may recommend polysomnography if he or she suspects you have:

    Sleep apnea or another sleep-related breathing disorder. In this condition, your breathing repeatedly stops and starts during sleep.

    Periodic limb movement disorder. In this sleep disorder, you involuntarily flex and extend your legs while sleeping. This condition is sometimes associated with restless legs syndrome.

    Narcolepsy. You experience overwhelming daytime drowsiness and sudden attacks of sleep in this condition.

    REM sleep behavior disorder. This sleep disorder involves acting out dreams as you sleep.

    Unusual behaviors during sleep. Your doctor may perform this test if you do unusual activities during sleep, such as walking, moving around a lot or rhythmic movements.

    Unexplained chronic insomnia. If you consistently have trouble falling asleep or staying asleep, your doctor may recommend polysomnography.



A K-complex is a waveform that may be seen on an electroencephalogram (EEG). It occurs during stage 2 of NREM sleep. It is the "largest event in healthy human EEG".[1] They are more frequent in the first sleep cycles.

K-complexes have two proposed functions:[1] first, suppressing cortical arousal in response to stimuli that the sleeping brain evaluates not to signal danger, and second, aiding sleep-based memory consolidation.



 is a non-invasive method[1] of monitoring human rest/activity cycles. A small actigraph unit, also called an actimetry sensor,[2] is worn for a week or more to measure gross motor activity. The unit is usually in a wristwatch-like package worn on the wrist. The movements the actigraph unit undergoes are continually recorded and some units also measure light exposure. The data can be later read to a computer and analysed offline; in some brands of sensors the data are transmitted and analysed in real time.


How is sleep regulated

Two internal biological mechanisms–circadian rhythm and homeostasis–work together to regulate when you are awake and sleep.  

Circadian rhythms direct a wide variety of functions from daily fluctuations in wakefulness to body temperature, metabolism, and the release of hormones.  They control your timing of sleep and cause you to be sleepy at night and your tendency to wake in the morning without an alarm.  Your body’s biological clock, which is based on a roughly 24-hour day, controls most circadian rhythms.  Circadian rhythms synchronize with environmental cues (light, temperature) about the actual time of day, but they continue even in the absence of cues. 

Sleep-wake homeostasis keeps track of your need for sleep.  The homeostatic sleep drive reminds the body to sleep after a certain time and regulates sleep intensity.  This sleep drive gets stronger every hour you are awake and causes you to sleep longer and more deeply after a period of sleep deprivation.

Factors that influence your sleep-wake needs include medical conditions, medications, stress, sleep environment, and what you eat and drink.  Perhaps the greatest influence is the exposure to light.  Specialized cells in the retinas of your eyes process light and tell the brain whether it is day or night and can advance or delay our sleep-wake cycle.  Exposure to light can make it difficult to fall asleep and return to sleep when awakened.

Night shift workers often have trouble falling asleep when they go to bed, and also have trouble staying awake at work because their natural circadian rhythm and sleep-wake cycle is disrupted.  In the case of jet lag, circadian rhythms become out of sync with the time of day when people fly to a different time zone, creating a mismatch between their internal clock and the actual clock. 


Anatomy of Sleep

Several structures within the brain are involved with sleep.

The hypothalamus, a peanut-sized structure deep inside the brain, contains groups of nerve cells that act as control centers affecting sleep and arousal.  Within the hypothalamus is the suprachiasmatic nucleus (SCN) – clusters of thousands of cells that receive information about light exposure directly from the eyes and control your behavioral rhythm.  Some people with damage to the SCN sleep erratically throughout the day because they are not able to match their circadian rhythms with the light-dark cycle.  Most blind people maintain some ability to sense light and are able to modify their sleep/wake cycle.

 The brain stem, at the base of the brain, communicates with the hypothalamus to control the transitions between wake and sleep.  (The brain stem includes structures called the pons, medulla, and midbrain.)  Sleep-promoting cells within the hypothalamus and the brain stem produce a brain chemical called GABA, which acts to reduce the activity of arousal centers in the hypothalamus and the brain stem.  The brain stem (especially the pons and medulla) also plays a special role in REM sleep; it sends signals to relax muscles essential for body posture and limb movements, so that we don’t act out our dreams.

The thalamus acts as a relay for information from the senses to the cerebral cortex (the covering of the brain that interprets and processes information from short- to long-term memory).  During most stages of sleep, the thalamus becomes quiet, letting you tune out the external world.  But during REM sleep, the thalamus is active, sending the cortex images, sounds, and other sensations that fill our dreams. 

The pineal gland, located within the brain’s two hemispheres, receives signals from the SCN and increases production of the hormone melatonin, which helps put you to sleep once the lights go down.  People who have lost their sight and cannot coordinate their natural wake-sleep cycle using natural light can stabilize their sleep patterns by taking small amounts of melatonin at the same time each day.  Scientists believe that peaks and valleys of melatonin over time are important for matching the body’s circadian rhythm to the external cycle of light and darkness.

The basal forebrain, near the front and bottom of the brain, also promotes sleep and wakefulness, while part of the midbrain acts as an arousal system.  Release of adenosine (a chemical by-product of cellular energy consumption) from cells in the basal forebrain and probably other regions supports your sleep drive.  Caffeine counteracts sleepiness by blocking the actions of adenosine.

The amygdala, an almond-shaped structure involved in processing emotions, becomes increasingly active during REM sleep. 


Delayed sleep phase disorder

Delayed sleep phase syndrome (DSPS) is a disorder in which a person’s sleep is delayed by two hours or more beyond what is considered an acceptable or conventional bedtime. The delayed sleep then causes difficulty in being able to wake up at the desired time.

The effects of DSPS

People with delayed sleep phase syndrome generally have difficulty:

Falling asleep, unless they go to bed very late (usually some hours after midnight) because their internal clock is sending alerting signals until late into the night

Waking up at a "normal" time in the morning, because their internal clock is not yet producing strong alerting signals.


Bright light therapy: We use light to gradually shift your sleeping pattern to a more conventional schedule. 

Chronotherapy: This technique aims to reset your circadian clock by slowly delaying your bedtime (and your sleep period) by about two hours every few days.  The disadvantage is that it disrupts your normal schedule of activity during the shift, when day and night are reversed.