PSYC 444 Lecture Notes - Lecture 6: Non-Rapid Eye Movement Sleep, Sleep Deprivation, Glymphatic System
14 May 2018
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PSYC 444 – LECTURE 6
WHAT IS SLEEP FOR? STATE OF ADAPTIVE INACTIVITY
Sleep is ubiquitous in the animal kingdom
• “ie all aials eed to sleep, aials aot e opared ased o those that sleep ad those that do’t.
Krueger et al. (2016): Six theories of sleep function
1. Host defense: immune system function
2. Conservation of energy: requires less eating throughout the day
3. Restoration of energy stores
4. Glymphatic function: removal of toxic by-products
5. Restoration of performance: cognitive functions
6. Sleep serves connectivity/plasticity: production of new neurons and synapses
Most likely has many functions.
• Nothing is well unless we sleep
Sleep is the ultimate unconscious state and is required for memory consolidation.
• In one study, participants were assigned to either repeat a set of words or do an unrelated activity. Those who did something else performed better when
later tested on those words. Some unconscious process has to occur in the brain in order to have better memory.
EVOLUTIONARY FUNCTION OF SLEEP
Why is sleep necessary?
• Sleeping animals are vulnerable to predators. Sleep must be advantageous in some way if it was conserved in all animals.
• Sleep: neural oscillations; active/quiet; NREM/REM
• Based on the current definition, it is difficult to say that organisms without a brain sleep, as there are no neural oscillations that can be measured
Sleep occurs in any organism with a neuronal-glial network
• Emergent property: it may be that organizing neurons in this network-like manner results in sleep
• Independent of anatomy
Above is a study examining whether the weight of animals is correlated with amount of sleep required
x-axis: weight (kg); y-axis: sleep per day (hours)
There is a connection seen in herbivores
• Example: elephants sleep three hours a day; gerbils sleep 15 hours a day
• It takes a lot of food to aitai eerg deaded elephats’ large od ass
• On the contrary, gerbils sleep for a long time. Thus, they require less food to maintain functioning during wake.
No connection seen in carnivores and omnivores.
• Length of sleep alone is insufficient to determine function of sleep
Even when comparing animals from the same phylogenetic order, animal relatives require different amounts of sleep
Shortest sleepers: elephants (4 hours a day)
Longest sleepers: koala (22 hours a day)
Humans are somewhere in between (8 hours a day)
DOLPHINS AND HALF-HEMISPHERIC SLEEP
Dolphins are special because if it possible for them to be awake and asleep at the same time. However, it is not that one hemisphere is completely awake and the
other completely asleep; it is more so that one is more awake or asleep than the other.
Even in humans, EEG with high temporal resolution show that there are areas of the brain that are ore aake tha other regios. Sleep stages are not equally
distributed at the same time point throughout the brain. However, we do not display half hemispheric sleep to the same extent as dolphins do.
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HOST DEFENSE (IMMUNE) THEORY OF SLEEP
What happens when we don’t sleep? There is less immune defense following sleep loss
• Not as many white and T-cells following sleep deprivation
• We take more naps and sleep for longer periods when sick
• This happens naturally. Thus, sleep must have an important function when sick
Sleep changes with disease are well-documented
• Organisms sleep more
• Possibly to conserve precious energy required for fighting the disease
o The priority is survival and removal of the virus. Sleep itself may not be important per se but we sleep more because it prevents energy
expenditure on other activities.
• However, not clear why it is important to be unconscious during sleep
Conventional wisdom: you have to sleep to heal
While ill, there is an increase in NREM sleep and decrease in REM
• Conclusion is that NREM sleep must be more important for recovery if there is an increase
• May be related to basic survival functions, whereas REM may be more important for cognitive functions.
PHYSIOLOGICAL FUNCTIONS OF SLEEP: IMMUNE SYSTEM
If ou do’t sleep eough, the iue sste is ot atiated as uh less optial futioig
• In one study, one group was sleep deprived and the other well-rested following vaccinations.
• After the immune system was activated to fight the virus, its functioning was measured.
• Conclusion: more sleep results in more immune system cells, such as white cells.
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Dotted line: sleep deprived individuals
Solid line: well-rested individuals
Measures: cortisol, prolactin, IL-2 and T-cells (two cells related to immune function)
Cortisol is driven mostly by the circadian rhythm. Thus, not every function suffers when sleep deprived.
On the contrary, the other measures are more sensitive to sleep deprivation.
This study involves short term sleep deprivation, not chronic deprivation.
SLEEP DURING FEVER
Red: fever measured in Celsius
Green: hypnogram measuring sleep pattern changes
Brain temperature increases during REM and decreases during NREM.
Data demonstrate increased survival when the host develops a moderate fever during bacterial or viral infections.
Increase in NREM sleep conserves energy
Fragmentation of NREM sleep reduces heat loss
• Decrease in sleep bout length
• Keep waking up
REM suppression leads to shivering, allowing fever production
Increase and decrease in NREM and REM respectively is proportional (not in terms of total sleep)
CONSERVATION AND RESTORATION OF ENERGY
We feel tired when sleep deprived and energetic after waking up. During daily functioning, some bodily activities must occur during sleep and others during wake.
There is a tradeoff: temporary inability to interact with the environment in exchange for a metabolic benefit for the whole body
• We engage in repair and increase our energy level during sleep
• Hoeer, e are teporaril off durig this tie siilar to a reoot
There is less glucose use in NREM SWS
• We have a finite amount of glucose (energy) we get from the food we eat
• Energy allocation model: sleep-ake le is a shedule of eerg iestets
CALORIC CONSERVATION
Sleep is involved in conservation of calories
• Lower body temperature during sleep
• Hibernation in some animals
• Reduced energy-use is likely to be adaptive
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Document Summary
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