functions of sleep 1 Flashcards
KRUGER ET AL (2016): 6 THEORIES OF SLEEP…
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
why is hard to know if other non animal organisms sleep
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
why do we consider sleep to be an emergent property of neural networks
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
sleep differences in types of animals
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
unihemispheric sleep
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
can humans have unihemispheric sleep?
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
🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬🐬
host defense theory of sleep
→ 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
how does sleep adapt to illness
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
conservation/restoration of energy
→ 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
conservation of energy in wake - gains and losses
Wake (gains)
- Vigilance
- Reproduction
- Foraging, food , etc
Wake (loss)
- Thermoregulatory effect
- Increased body temp
sleep gains and losses (conservation/restoration of energy)
Sleep (gains)
- Growth
- Maintenance
- Repair
- Immune function
- Neural network regeneration
Sleep (loss)
- Vigilance
Productivity
caloric conservation in sleep
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
glymphatic function in sleep
→ 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
astrocyte function
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
glymphatic function and alzheimers
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
connectivity/plasticity promotion in sleep
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
tononi’s synaptic homeostasis hypothesis
· 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
what occurs in wake, according to tononi?
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….
what happens in sleep according to tononi?
desaturation of plasticity
Prune out new connections, restore extracellular space
Restore:
○ Energy
○ Supplies
○ Cellular homeostasis
○ Extracellular space
○ Vigilance
○ Cognition
○ Learning
Memory consolidation and integration
synaptic potentiation in wake
- Current sampling - details (prof wears shirt, has this colour water bottle, said this and that)
Synaptic potentiation - all the small stuff
synaptic potentiation in sleep
- 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
what are the specific mechanisms of sleep and homeostasis
· 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
neurogenesis
- 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
- Sleep role in hippocampus - dependent learning/emotion regulation - sleep role in neurogenesis
restoration of performance (cognitive functions)
→ Memory
→ Reflexes
→ Attention
→ Mood
→ Emotional reactivity
Emotion
brain area takeover theory
Rem= fools our occipital areas that we’re still living the bright world, so they don’t takeover other brain areas during darkness
developmental shifts in function theory (about the nature of rem sleep)
· 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
