functions of sleep 1

Question 1

KRUGER ET AL (2016): 6 THEORIES OF SLEEP…

Answer 1

Sums up what we know:
· Host defense - fix ourselves
· Conservation of energy
· Restoration of energy stores
· Glymphatic function: removing toxic by products
· Restoration of performance (cognitive functions)
· Serves connectivity/plasticity

Question 2

why is hard to know if other non animal organisms sleep

Answer 2

The definition of sleep: neural oscillations (active/quiet; nrem/rem), makes it hard for us to know if plants and stuff that doesn’t have a neural network sleep

Question 3

why do we consider sleep to be an emergent property of neural networks

Answer 3

Pretty much appears in any organism with a neuronal-glial network (krueger et al, 2016)
○ Emergent property - a bunch of basic features come together to make something complex - comes out of a system but not exactly explained by the system itself
○ Independent of anatomy?
Has a function? We don’t know

Question 4

sleep differences in types of animals

Answer 4

herbivores: bigger they get, the less they sleep (need more time to eat)

carnivores: sleep more generally

wide variability in sleep niches - animals that sleep just as much as us or have same rem can be very different
…..means that when we do animal models of sleep and superimpose them on human brains it might not be totally accurate

longest sleep: koala = 22hrs
shortest sleep: elephant = 4hrs

Question 5

unihemispheric sleep

Answer 5

Some animals can sleep one hemisphere at a time
🦦OTTERS - sleep unihemispheric in water and both hemispheres on land
🐬DOLPHINS - need to come up to breathe
🦜SOME BIRDS - need to sleep in flight

Question 6

can humans have unihemispheric sleep?

Answer 6

Humans can’t sleep one hemisphere at a time, but we can have LOCAL sleep
Ex. Sleep walking - some areas in sws and others almost awake
🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬

Question 7

host defense theory of sleep

Answer 7

→ To ward off sickness - when you’re sick go to bed
→ Sleep loss = less immune function
→ Sleep changes with disease are well documented
○ Organisms sleep more
○ Possibly to conserve precious energy required for fighting the disease
○ Not clear why it is important to be unconscious during sleep - know that quiescence is important to recovery but why unconscious?

Bed rest… 🛏 🛏 🛏 🛏 🛏 🛏 🛏 🛏 🛏
▪ Yes, do go to bed when you are ill (not w laptop)
While sick: increase in nrem sleep and decrease in rem

Question 8

how does sleep adapt to illness

Answer 8

altered sleep makes the immune system more efficient:
- fragmented
- nrem goes up
- bouth length in nrem goes down (fragments)
- rem goes down
- heat production goes up (fever)
- heat loss goes down (fever)
- means that temperature becomes suboptimal for pathogen replication and they become more sensitive to actions of host system

unclear is sleep directly promotes healing or just makes the optimal conditions for promoting immune function

Question 9

conservation/restoration of energy

Answer 9

→ Economical system: trade off - temporary inability to interact with the environment but a metabolic benefit for the whole body
→ Less glucose uses in nrem sws
Energy allocation model: sleep - wake cycle is a schedule of energy investments

Question 10

conservation of energy in wake - gains and losses

Answer 10

Wake (gains)
- Vigilance
- Reproduction
- Foraging, food , etc

Wake (loss)
- Thermoregulatory effect
- Increased body temp

Question 11

sleep gains and losses (conservation/restoration of energy)

Answer 11

Sleep (gains)
- Growth
- Maintenance
- Repair
- Immune function
- Neural network regeneration

Sleep (loss)
- Vigilance
Productivity

Question 12

caloric conservation in sleep

Answer 12

Sleep conserves calories - use less energy when we sleep
- Lower body temp in sleep
- Hibernation
- Reduced energy use - likely to be adaptive
- Short sleepers more at risk of stuff like diabetes, obesity, cravings for carbs
Chronic sleep deprivation also effects metabolism - worse at metabolizing glucose

Question 13

glymphatic function in sleep

Answer 13

→ People used to think that glial cells were just in body and brain (lots in brain) for “structural support”
→ 2012 - observed that astrocytes (type of glial cell) create pathway between different fluids in the brain to carry away different metabolic products/waste - looks like it happens through glial cells
○ Eliminates neurotoxins, including amyloid beta
○ Whole system seems more active in sleep; less active during wake
Glial cells function like lymphatic system - called glymphatic function/system

Question 14

astrocyte function

Answer 14

ASTROCYTES (one type of glial cell) : create fluid conducting channels in the vicinity of the blood vessels
- Facilitates distribution of important molecules for brain functioning: fluid flows through the brain tissues
- Influx: lipids and other molecules
Outflow: metabolic waste

Question 15

glymphatic function and alzheimers

Answer 15

impaired, fragmented sleep = astrocytes don’t work as well - create messy pathways.. And don’t clear away beta amyloid - (alzheimers is caused by beta amyloid plaques disrupting neural function in the brain)
More alzheimers means less sleep and less clearance, creating a bidirectional relationship

Question 16

connectivity/plasticity promotion in sleep

Answer 16

Brain isn’t an archive - plastic, dynamic organ that changes depending on what you do with it….be careful what you do with it
→ Brain connections change with the passage of time in relation to environmental challenges and life experiences (learning)
→ Neurons that fire together wire together (hebbian learning) - stuff becomes flowy and easy the more we entrain ourselves
○ new synapses - wake; then pruning 🌳 sleep
○ Trade off: rigidity and flexibility
Make more synapses that we would ever need during wake - need to prune them off during sleep…don’t have enough brain room

Question 17

tononi’s synaptic homeostasis hypothesis

Answer 17

· New learning should happen primarily by synaptic potentiation - in other words, when you learn something, a bunch of neurons will have an easier time being activated together. However, firing that signals suspicious coincidences can percolate throughout the brain (ex. Always thinking of prof and black shirts)

· Synaptic potentiation should occur primarily in wake - when organism interacts with environment, not in sleep when it is disconnected - what we learn is controlled by reality

Renormalization of synaptic strength should happen primarily during sleep, when the brain is spontaneously active off line, not in wake when a neuron’s inputs are biased by a particular situation - getting rid of suspicious connections

Question 18

what occurs in wake, according to tononi?

Answer 18

net value of synaptic strength goes up, strsss for neurons, extracellular space, need for energy, supplies
= saturation of plasticity - don’t need to be actively learning, just live life

As we get saturated, there start to be costs
○ Vigiliance
○ Cognition
○ Learning
Time for sleep….

Question 19

what happens in sleep according to tononi?

Answer 19

desaturation of plasticity
Prune out new connections, restore extracellular space
Restore:
○ Energy
○ Supplies
○ Cellular homeostasis
○ Extracellular space
○ Vigilance
○ Cognition
○ Learning
Memory consolidation and integration

Question 20

synaptic potentiation in wake

Answer 20

• Current sampling - details (prof wears shirt, has this colour water bottle, said this and that)
  Synaptic potentiation - all the small stuff

Question 21

synaptic potentiation in sleep

Answer 21

• Forget the non salient details during sleep, just remember the meaningful changes/relevant stuff - synaptic down selection
  In the end, we just have the concept (prof) - comprehensive sampling

Question 22

what are the specific mechanisms of sleep and homeostasis

Answer 22

· Renormalization during sleep: nrem sleep - UP stages of cortical slow waves; and UP states of hippocampal sharp waves (brief bursts of high frequency electrical activity that occur during sws, rest, and immobility - thought to be involved in memory consolidation, replay of experiences and pattern completion (for memory))

Synaptic level: accumulation of specific proteins indicative of synaptic weakening

Question 23

neurogenesis

Answer 23

• New neurons grow in hippocampus even in adulthood
  
  • Sleep role in hippocampus - dependent learning/emotion regulation - sleep role in neurogenesis
    Chronic sleep disruption - less neurogenesis

Question 24

restoration of performance (cognitive functions)

Answer 24

→ Memory
→ Reflexes
→ Attention
→ Mood
→ Emotional reactivity
Emotion

Question 25

brain area takeover theory

Answer 25

Rem= fools our occipital areas that we’re still living the bright world, so they don’t takeover other brain areas during darkness

Question 26

developmental shifts in function theory (about the nature of rem sleep)

Answer 26

· Sleep shifts in age
· Functions of rem and nrem change in age - from reorganization to repair
· Infants = more time in rem sleep, potentially different role of rem
· Sleep for neural reorganization until 2-3 years - making of a human…. and then when older for repair and clearance (keep brain together)
By 2.4 years brains are pretty much grown (80-90% adult size) white matter changes, growth of connectvity - critical periods for learning and stuff