W7L1 - Function of Sleep

Question 1

What are three study methodologies of sleep

Answer 1

• Disrupt sleep and look at consequences
  
  • (e.g, deprivation > cognitive task)
• Modify “function factor” and look at sleep
  
  • (e.g., give immune drug and see if it affects sleep)
• Evolution/comparative aspects
  
  • (e.g. cross species)

Question 2

What are two limiations of sleep research

Answer 2

• Most research looks at correlation versus causation
• REM versus NREM sleep (might serve different function)

Question 3

Rechtschaffen et al. (1989) Sleep Study: Method

Answer 3

‘Disk over Water Method’

• Yoked Control
• Sleep Deprived Sleep
  
  • EEG electrodes in brains and EMG electrodes in musculature > connected to the computer.
  • When sleeping, slippery disc will rotate and rat will get wet
• Both groups subjected to same conditions except sleep

Question 4

Rechtschaffen et al. (1989) Sleep Study: 4 Results

Answer 4

Results

1.)

• Total Sleep Deprivation Rats died after 11-32 days
• Causes was ambiguous (some infection, organ failure, etc)

2. )
   * Yoked controls were sacrificed within 30 minutes of their experimental pair dying.
3. )
   * Rats deprived of food (ad lib water) lived about 30 days.
4. )
   * Rats deprived of REM only died after 16 - 54 days

Question 5

Rechtschaffen et al. (1989) Sleep Study: Conclusion

Answer 5

Extended sleep loss reliably produces a syndrome of specific, substantial physiological changes

• Mortality (Ambigious)
• Scrawny
• Intial rise in intraperitonal temperature, followed by large reduction
• > Food intake; > Energy Expenditure; < Body weight
  
  • Theory of Energy Conservation
• Total recovery from symptoms after recovery sleep
• Localised severe skin lesions

Question 6

Energy Conservation Theory: Weak and Strong Form

Answer 6

Weak Form

• Immobility is associated with lower levels of energy expenditure than activity. Immobility itself conserves energy
  
  • Sitting still and not moving = Expending less energy than you are moving around

Strong Form

• Sleep actively lowers energy expenditure below that of immobile wakefulness
  
  • Lying in bed awake you are = Expending more energy than if you are lying in bed asleep.

Question 7

Sleep and Human Experiment. Evidence for ciracadian-related influence.

Answer 7

Measured by input and ouput of O₂ and CO₂

• Drop in O₂ input and CO₂ output
• Increase in O₂ input and CO₂ output before waking up
  
  • Possible that it is ciracadian-related. Always reduction due to biological rhythm

Question 8

Sleep and Human Experiment. Evidence against ciracadian-related influence.

Answer 8

O₂ consumption falls with sleep and time

• Condition 1: Regular
  
  • Big reduction in energy expenditure sustained across the night
• Condition 2: Stay awake for the first three hours of the sleep period
  
  • Larger drop in energy expenditure when you let them sleep which continues to reduce for the rest of the 3-4 sleep period
• Condition 3: Deprive the person of sleep the whole night up until an hour before they would usually go to bed
  
  • Energy expenditure is sustained throughout the night and then has a massive drop when the person is allowed to sleep.
• Evidence that energy expenditure is actively reduced during sleep.

Question 9

Collet et al. (2016): If energy intake affects sleep

Answer 9

• Baseline with caloric intake fixed at required level
• After 2 days, caloric restriction to 10% of requirements
• After 2 days, of ad lib food recover

Results

• Not enough calories > Stage 4 Sleep (SWS) Increase; Not REM or Light
  
  • Suggest less energy = more deep sleep to conserve

Question 10

What are criticisms of energy conservation theory

Answer 10

• Fall in metabolic rate during sleep is small in magnitude
  
  • Staying up all night only 150 calories
• Active heat loss associated with sleep onset.
  
  • Reduction in temperature to sleep, but creating heat uses a lot of energy > Counterintuitive
• Negative correlation over species between (absolute) basal metabolic rate and sleep duration in mammals
  
  • Bigger animals sleep less

Question 11

Sleep Across Species: Do all animals sleep? Several definitions

Answer 11

Depends on defintion

Definition 1: Reduced Responsiveness, etc

• Yes

Definition 2: Homostaetic Sleep Drive

• All but mollusc (snails)

Definition 3: High Voltage Slow Wave (SWS)

• All mammals

Definiton 4: REM/NREM sleep

• Primates, mammals (except dolphins), monotremes, birds
• Not present in fish, mollsucsc and insects

Question 12

REM in mometremes and ostrich

Answer 12

Mix of REM and SWS

Question 13

Phylogenetic studies on sleep:

Answer 13

Some point in history, 2 animals will be the same sleep but after that point, it changed.

Evolution favoured a type of sleep and this type of sleep developed in these animals separately

1. ) Body Mass
2. ) Encephalisation
3. ) Preadtors

Question 14

Is body mass relate to sleep qualities in animals?

Answer 14

Herbivores

• Negative correlation between the sleep duration and body mass
• Possible that time herbivore take to eat outweigh benefits of sleep

Carnivores and Omnivores

• No correlation
• Possible that they source food easier and more time to sleep

Question 15

Degree of enchephalisation (Brain size) and sleep

Answer 15

Relative brain size (to copy):

• Positively related to %REM, but not SWS
  
  • Weak relationship (r²=0.04)
• Related to the sleep cycle length
  
  • 10 mins in mice, 90 mins in humans, 120 mins in elephants

Question 16

Other than body mass and brain size, what other factors affect sleep?

Answer 16

Number of predators

• Negatively related to amount of sleep
• More predator = Less Sleep

Question 17

What is the immobility hypothesis? Implication?

Answer 17

Immobility Hypothesis

• Circadian system causes rest-activity cycle.
  
  • Sleep has evolved to ensure immobility during the rest phase.
  • Therefore, supporting and reinforcing circadian organisation of behaviour

Implication

• Sleep no longer serves a purpose in humans as we have so engineered our environment that food is always available and it is no longer dangerous to be active during the dark phase.
• However, because the mechanism still exists we are obliged to continue to sleep.

Question 18

What is a major evidence of the immobility hypothesis?

Answer 18

Sleep of species appears to fit with their ecologic niche.

However, argument is retrospective and circular.

Question 19

Conclusion from phylogenetic studies

Answer 19

• Large variation in sleep amounts
• Variation not predicted by phylogenetic order (e.g. primates as a group are not distinguishable from other species)
• While there is some relationship between sleep duration/cycle duration and animal characteristics
  
  • Function of sleep is still unknown.

Question 20

Sleep properties in the cetaceans (dolphins)

Answer 20

• Unihemispheric sleep (To sleep in water)
  
  • One hemisphere of the brain is asleep and have slow wave activity
  • Other hemisphere of the brain is active and awake
• No REM sleep
  
  • If they had REM, muscle paralysis would cause drown
• Many subspecies are rarely immobile (some species do float, or rest on the bottom)
• Limited evidence suggests weak rebound
  
  • Reduced hemeostatic effect; don’t need to recover

Question 21

Postpartum sleep in cetaceans: No Rebound

Answer 21

Sleep

• indicated by sleep behaviour (floating and lying at the bottom of the pool);and
• eye closure (eye closure occurs in association with contra-lateral SWA) is minimal in both the neonate and mother

Their sleep need disappears and there is no homeostatic sleep rebound either.

Question 22

Sleep of Fur Seals

Answer 22

Winter (In water)

• Unihemispheric Slow Wave Activity (SWA)
• Severely reduced REM sleep
• Motor asymmetry
  
  • Flipper contra-lateral to the sleeping hemisphere is immobile
  • Whiskers contra-lateral to the awake hemisphere used to monitor position

Summer (On land)

• Bilateral NREM and REM
• No REM rebound during the immediate post-winter period