Week 8-Sleep

Question 1

How much of our lives on average do we spend sleeping?

Answer 1

On average, you would spend 1/3 of your life
sleeping (8 hours/day) aka 175,000 hours

Question 2

What’s sleep?

Answer 2

-Sleep is a universal behaviour displayed by all mammals and birds (Reptiles, fish amphibians and insects enter periods of quiescence that resemble sleep but only warm blooded vertebrates exhibit REM sleep)
-Sleep is not distinguished by movement
-Sleep involves a change of consciousness

Question 3

What are the motivational characteristics of sleep?

Answer 3

-Find a suitable sleeping location
-Persuaded to go there by onset of sleepiness

Question 4

How do we study sleep?

Answer 4

The best research is carried out in sleep laboratories

Question 5

What are the physiological changes in sleep?

Answer 5

• Physiological variables are controlled during wakefulness at levels optimal for body functioning
  o Brain wave activity, breathing and heart rate vary.
  o Temperature, blood pressure and levels of carbon dioxide, oxygen and glucose are kept quite constant.
• Physiological demands are reduced during sleep
  o Brain wave activity, breathing and heart rate become extremely regular
  o Levels of other variables (temperature etc) tend to drop

Question 6

How does temperature fluctuate during sleep?

Answer 6

-During wakefulness, body temperature fluctuates minimally around a set point
-Prior to sleep bodies begin to lose heat – cue to induce sleep?
-Core temperature reduced by 1-2 oC during non-REM sleep – reduced energy demands
-Temperature falls to lowest levels during REM sleep

Question 7

How does respiration and cardiovascular activity fluctuate during sleep?

Answer 7

-Breathing is quite irregular during wakefulness
-With progression through stages of non-REM sleep breathing rate decreases and becomes very regular
-Heart Rate increases and/or varies again with REM sleep
-Heart rate and blood pressure follow a similar pattern
-Variations in REM sleep may be a by-product of nervous system activity or related to dream content

Question 8

Which physiological activities decreases during sleep?

Answer 8

o Kidney function slows
o Urine production is decreased

Question 9

Which physiological activities increases or is maintained during sleep?

Answer 9

o Increase in growth hormone release
o Activities associated with digestion, cell repair and growth are greatest during sleep

Question 10

Define Electroencephalogram (EEG)

Answer 10

Electrodes attached to the scalp record electrical activity of the brain.

Question 11

Define Electromyogram (EMG)

Answer 11

Electrodes attached to the chin monitor muscle activity

Question 12

Define Electro-oculogram (EOG)

Answer 12

Monitors eye movements

Question 13

What are the EEG waves present when awake, but non-attentive?

Answer 13

Large, regular alpha waves, more prevalent with eyes closed

Question 14

What are the EEG waves present when awake, but attentive?

Answer 14

-Low amplitude, fast, irregular beta waves
-Beta waves are desynchronised: many circuits are active

Question 15

What occurs in the first stage of sleep? NREM

Answer 15

-Brief transition stage when first falling asleep - theta waves
-Stage 1 is a transition between wakefulness and sleep and if you observe the subject the eyes open and roll
-Lasts about 10 minutes
-Hypnagogic hallucinations: vivid and frightening episodes of seeing, hearing or feeling phantom sensations while falling asleep. Also sensation of falling

Question 16

What occurs in the second stage of sleep? NREM

Answer 16

-The subject is sleeping soundly now but if you wake him up he might report that he has not been asleep (15 minutes)
-Stage 2 is characterised by sleep spindles and K complexes
-Sleep spindles: short bursts of waves that occur between 2 and 5 times per minute in stages 1-4. They seem to play a role in consolidation of memories
-Increased number of spindles are correlated with increased scores on intelligence tests
-K complexes: usually found ONLY in stage 2. Triggered by noises. Important in consolidation of memories (lost in schizophrenia)

Question 17

What occurs in stage 3 and 4 of sleep? NREM

Answer 17

-(slow-wave sleep): Characterised by an increasing
percentage of slow, irregular, delta activity
-The distinction between stage 3 and 4 is not clear cut
-Stage 3: 20-50% delta activity and stage 4 over 50% delta activity
-Because slow wave predominates usually these stages are called slow wave sleep
-By most criteria stage 4 is the deepest sleep: only awakened by loud noises, when awakened groggy and confused

Question 18

What occurs during REM?

Answer 18

-About 70 minutes after the onset of sleep (40 mins after onset of stage 4) there is an abrupt change of physiological measures
-EEG desynchronised
-Eyes moving beneath closed eyelids
-Muscle activity becomes silent: profound loss of muscle tone
-Apart from occasional twitching a person becomes paralysed during REM sleep
-During REM sleep a person might not react to noises but is awakened by meaningful stimuli such as calling their names
-When awakened from REM sleep they are alert and attentive but have been dreaming

Question 19

How long are sleep cycles?

Answer 19

-During the night people alternate between periods of REM and NREM
~90-minute cycles

Question 20

What does the amount of REM sleep needed correlate with?

Answer 20

-The amount of REM sleep needed correlates with immaturity at birth
-This suggests that REM sleep might have a role in brain and body development
-Birds have a few seconds of REM sleep. Reptiles do not have it
-REM evolved with homeothermy?

Question 21

How much REM sleep do babies undergo?

Answer 21

-Babies can go directly from wake to REM
spend 50% in REM in the first weeks
Not clear why the amount of sleep declines with age:
-Decreased need
-Decreased ability of sleep mechanisms

Question 22

How much proportion sleep occurs after adulthood?

Answer 22

-Proportion REM sleep does not change after adulthood
-Proportion NREM sleep declines continuously
-The primary purpose of REM sleep is to act as an “inducer” of CNS development in the foetus and the newborn
-In animals suppression of REM affects CNS maturation

Question 23

Why do we sleep?

Answer 23

• With the exception of avoiding severe pain and need to breath, sleepiness is probably the most insistent drive that we can experience.
• We cannot defy the urge to sleep indefinitely.
  Two theories:
• Recuperation theory
• Adaptation theory

Question 24

What’s recuperation theory?

Answer 24

-Being awake disrupts the internal physiological stability (homeostasis) and sleep is required to restore it
-If this was the case who would need more sleep? A horse or a sloth?
-Sloths need 20 hours of sleep…. and horses only 3
* Being awake disrupts homeostasis – sleep restores it
* Primary function of slow wave sleep: allow the brain to rest.
* Slow wave sleep and REM sleep also promote different types of learning and memory.
* REM sleep promotes brain development.

Question 25

What’s adaptation theory?

Answer 25

-Sleep is the result of an internal 24-hour
timing mechanism: we are programmed to sleep at night regardless of what happens to us during the day
-Evolutionary advantage of sleeping during the night??? Sleep protects us from accidents and predation during the night

Question 26

What are the symptoms of sleep deprivation?

Answer 26

 Tiredness
 Irritability
 Edginess
 Inability to tolerate stress
 Problems with concentration & memory
 Behavioural, learning, social problems
 Frequent infections
 Blurred vision
 Vague discomfort
 Alterations in appetite
 Activity intolerance

Question 27

What fundamental problem is there when we interpret these sleep deprivation symptoms?

Answer 27

In Western cultures, most problems with sleep are the result of stress, so you need to be careful when saying that lack of sleep causes all those symptoms, it could just be the effects of stress

Question 28

What predictions of recuperation theories are there about sleep deprivation?

Answer 28

Because this theory is based on the premise that sleep is a response to the accumulation of some debilitating effect of wakefulness, three predictions
are made about the effects of sleep deprivation
1- Long periods of wakefulness will produce physiological and behavioural disturbances
2- These disturbances will grow steadily worse as the deprivation continues
3- After the period of deprivation has ended much of the missed sleep will be regained

Question 29

What happens when we don’t sleep?

Answer 29

Two initial studies:
1- The sleep-deprived students (Kleitman, 1963)
2- The case of Randy Gardner (Dement, 1978)
Randy Gardner went to sleep 264 hours and 12 minutes after he had awakened 11 days before and slept 14 hours the first night and went back to the usual 8 hours schedule.

Question 30

What is the case of Peter Tripp?

Answer 30

• Radio presented in New York
• Stayed awake for 8 days and nights as part of a charity fund raising stunt
• Initially coped well – observations consistent with other studies
• Day 4 – experienced hallucinations and psychotic symptoms
• Day 8 – essentially “lost his mind”
• Slept for 22 hours after completed 8 days without sleep
• Long term consequences – psychotic symptoms, lost his job, divorced his wife, rarely heard of again!

Question 31

What’s the Carousel apparatus?

Answer 31

*Disk rotates when the animal falls asleep
*Pushed off disk into water
*Died after 12 days
*Post-mortem evidence of stress
*Deprivation studies can be difficult to interpret

Question 32

Why are the results of sleep deprivation studies not conclusive?

Answer 32

*Sleep deprivation does not interfere with the ability to perform physical exercise
*No evidence of physiological stress response to sleep deprivation
*Thus the primary role of sleep does not seem to be rest and recuperation of the body
*Cognitive abilities are affected: perceptual distortions and even hallucinations.
*After sleep deprivation never regain all the lost sleep.

Question 33

What 2 consistent effects are caused by REM sleep deprivation?

Answer 33

1- Following REM-sleep deprivation there is a REM rebound: have more than the usual amount of REM sleep
2- With each successive night of REM deprivation there is a greater tendency to initiate REM sequences: First night have to be awakened 17 times during 7th night had to be awakened 67
times
(little or no effect on sleep within 2 weeks)

Question 34

What are the two main theories of the functions of REM sleep?

Answer 34

• Role in memory consolidation
• Default theory
  Role in memory consolidation: although seemed well demonstrated there are arguments against it:
• Why patients that take antidepressants, which reduce REM sleep duration, have no obvious
  memory problems?
• Several studies have failed to support a mnemonic function of REM sleep deprivation

Question 35

Why do we sleep?

Answer 35

-Brain is 2% of body weight but uses 20% of energy during quiet wakefulness.
-Cerebral blood flow and metabolism fall to around 75% during stage 4 sleep.
-Regions with highest level of activity during wakefulness show the highest levels of delta waves and lowest metabolic activity.
-These results suggest that during stage 4 the brain is indeed resting.
-So evidence suggests that the brain needs to rest to recover from the adverse side effects of wakefulness

Question 36

What are the functions of REM sleep?

Answer 36

REM sleep is completely different from slow-wave sleep therefore it would be unreasonable to expect REM sleep to have the same function as slow-wave sleep

Question 37

What’s the default theory?

Answer 37

-It is difficult to stay continuously in NREM sleep so the brain needs to switch to one of two other states
-If there is an immediate body function to take care of (i.e. need for food or water)=wakefulness
-If there are no immediate needs=REM sleep
-So REM sleep is more adaptive when there are no immediate needs
-In addition, according to this theory REM sleep prepares organisms for wakefulness is natural environments where immediate activity might be needed upon wakening REM and wakefulness are similar

Question 38

How did Nycamp et al’s (1998) study support this theory?

Answer 38

-Participants awakened every time they entered REM sleep
-Instead of letting them go back to sleep they had to be awake for 15 mins (substituting REM sleep for wakefulness)
-Under this condition the participants, unlike the controls, were NOT tired the day after despite getting only 5 hours of sleep
-What about the REM rebound? It did NOT happen
-In other words… there seems to be NO need for REM sleep if periods of wakefulness substitute it
-This is consistent with the finding that as antidepressants reduce REM, the number of night-time awakenings increase

Question 39

What are the functions of REM Sleep?

Answer 39

• Highest proportion is seen during the most active phases of brain development.
• Infants born with immature brains spend more time in REM sleep than infants born with well developed brains.
• If REM sleep functions in brain development why do adults have it?
• It has been suggested that REM also facilitates learning.
• Sleep aids in the consolidation of long-term memories (Marshall and Born 2007).
• REM sleep seems to consolidate non-declarative memories while slow stage sleep has an effect on declarative memory.

Question 40

How does the sleep cycle stage affect dreams? (Suzuki et al 2004)

Answer 40

-If awakened during NREM and ask people if they were dreaming they’ll probably say “no”
-If you question more carefully they’ll report the presence of some image or emotion (I was falling)
-On the other hand dreams of REM sleep tend to be narrative in form with a story like progression of events
-Initially it was assumed that dreams only happened during REM sleep
-Even when reporting dreaming when awakened during NREM, the dreams were attributed to remembering pervious dreams that happened during REM
How to study ONLY NREM:
-BY using short naps ensuring people DO NOT reach REM sleep stage
-This study reported that 18% of the NREM naps were associated with dream experiences

Question 41

How are dreams and memory consolidation linked?

Answer 41

-The discovery of memory reactivation during sleep
certainly suggests a parallel with dreams of recent
experience
-Memories Are “Reactivated” in the Sleeping Brain
-Rats reactivate hippocampal neurones used in a
maze
-In rodent studies, memory reactivation has most often been reported to occur in NREM sleep.
-Within NREM sleep, reactivation is expressed most strongly immediately after learning. The strength of this reactivation effect then tends to decay quickly across time
-Learning-related neural activity is not reactivated exactly in its original form.
-Waking firing sequences are reactivated in intermittent bursts, on a faster timescale than the original experience the “replay” is not always precise

Question 42

How is dreaming about learning experiences associated with enhanced memory?

Answer 42

-After reading the text of a short story, participants who reported dreams related to the story exhibited superior memory for the text the following morning
-Objections to this: dreams are not an accurate replay of waking experience
-Waking experience: “ When I left Starbucks, we had so many leftover pastries and muffins to throw away or take home. I couldn’t decide which muffins to take and which to toss…”
-Corresponding dream experience: “My dad and I leave to go shopping. We go from room to room, store to store. One of the stores is filled with muffins, muffins, muffins from floor to ceiling, all different kinds, I can’t decide which one I want…”

Question 43

Why has it been argued that the effect of sleep on memory is not merely to consolidate experience in its original form?

Answer 43

Because instead, sleep transforms memory traces over time, allowing us to:
- extract generalisations
- integrate information
- arrive at creative insights

-Sleep is a time when recently encoded information is “interleaved” into related memory networks
-This could be achieved by simultaneously reactivating recent and remote memory fragments, slowly associating new content into cortical semantic networks

Question 44

Why are the brain mechanisms for dreaming likely not identical to those responsible for memory consolidation?

Answer 44

-Although the content of dreams is influenced by memory consolidation, it may be that not every element of every dream is related to this process
-If conscious experience during sleep is the emergent result of neural activity distributed across much of the brain, only a portion of this activity would be expected to be influenced by the activity of memory systems
-Dreaming reflects the functional brain process of memory consolidation, but this does not mean that dreams, per se, have a function

Question 45

How are depression and REM sleep linked? (Palagnini et al., 2013)

Answer 45

-Depressed individuals show higher amygdala activation during REM sleep
-The majority of effective antidepressant drugs suppress REM sleep
-REM sleep changes in depression might be under a genetic control
-Genes that may be related to depression include cholinergic receptor genes that are involved in REM regulation, circadian clock genes and REM sleep regulation by hypocretin that is involved in REM sleep dysregulation, depression and stress