Lecture 13 function of sleep Flashcards
What are some things to consider when studying sleep
STUDY METHODOLOGIES
Disrupt sleep and look at consequences
Modify “function factor” and look at sleep
Evolution/comparative aspects
CONSIDERATIONS
Correlation versus causation
REM versus NREM sleep
What is the result of total sleep deprivation in the rat
They had 10 yoked controls and 10 total sleep deprivation
four conditions
1. Total Sleep Deprivation Rats died* after 11-32 days
Causes was ambiguous
Infections, organ failure, hypothermia, malnutrition
- Yoked controls were sacrificed within 30 minutes of their pair dying.
- Rats deprived of food (ad lib water) live ~30 days.
- Rats deprived of REM only died after 16 - 54 days
What are symptoms of total sleep deprivation in rats
Mortality (cause ambiguous)
Scrawny, debilitated appearance
Localised severe skin lesions
Initial rise in intraperitoneal temperature, followed large reduction
>Food intake energy expenditure
Total recovery from these symptoms with recovery sleep
What was the effect of total sleep deprivation on energy expenditure, body weight and food intake in rats
Both food intake and energy expenditure went up and weight went down, Total sleep deprivation shows greater effect than control
describe the strong and weak form of energy conservation theory
Weak Form
Immobility is associated with lower levels of energy expenditure than activity. Thus immobility itself conserves energy.
Strong Form
Sleep actively lowers energy expenditure below that of immobile wakefulness
What is the pattern of energy expenditure in a day and what is it related to
oxygen intake drop during sleep, independent of circadian rhythm as shown by study
o2 consumption used as an indicator of energy expenditure
describe a study in support of energy conservatio ntheory
12 Healthy men: Sleep studies done at:
Baseline with caloric intake fixed at required level
after 2 days caloric restriction to 10% of requirements
After 2 days of ad lib food recovery
sleep especially SWS increased during caloric restriction
describe criticisms of energy conservation theory
Fall in metabolic rate during sleep is small in magnitude.
Active heat loss associated with sleep onset.
Negative correlation over species between (absolute) basal metabolic rate and sleep duration in mammals. Note- there is no relationship in birds.
how does sleep vary across species
all animals show sleep of some sort
note - reptiles, fish, moluscs and insects don’t show high voltage slow waves and REM sleep - potentially due to small numbers of neurons
What is weird aobut monotremes’ sleep
they show a mix of sws and rem - sws with eye movement and rem atonia after rem started….
describe phylogeny of sleep
i think sws dropped off for birds of evolved for other animals but
I REALLY NEED TO CHECK WITH LECTURE RECORDINGS I GOT NO NOTES ON THIS
association between total daily sleep time and animals
pretty random
we see a neg correlaiton between body mass and sleep duration in all animals and herbivore and to some extent omnivore, but not in carnivore
degree of enchephalisation and sleep
The size of the brain relative to the body is:
Positively related to %REM, but not SWS
But this is a weak relationship (r2=0.04)
Related to the sleep cycle length
10 mins in mice, 90 mins in humans, 120 mins in elephants
what are the factors associated with sleep
number of predators, body size (also dependent on type of animal), brain size
number of predators and sleep
Number of predators
Negatively related to amount of sleep
describe immobility hypothesis
Circadian system causes rest-activity cycle.
Sleep has evolved to ensure immobility during the rest phase.
Thus, sleep acts to support and reinforce the circadian organisation of behaviour.
An implication of the immobility hypothesis is that 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.
evidence and drawback of immobility hypothesis
The major evidence in support of the immobility hypothesis is that the sleep of species appears to fit with their ecologic niche.
The major negative feature of this evidence is that the argument is retrospective and circular.
some random conclusions of phylogenetic studies
Large variation in sleep amounts
Variation not predicted by phylogenetic order (e.g. primates as a group are not distinguishable from other species)
Some relationship between sleep duration/cycle duration and animal characteristics but the function of sleep is still unknown.
Sleep Properties in the Cetaceans
Unihemispheric Sleep
No evidence of REM sleep
Many subspecies are rarely immobile (some species do float, or rest on the bottom)
Limited evidence suggests weak rebound (reduced homeostatic effect)
Postpartum Sleep in Cetaceans
Sleep, as indicated by both 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 postpartum
sleep properties of fur seals
Winter (Live in the water)
Unihemispheric SWA
Motor asymmetry
Flipper contra-lateral to the sleeping hemisphere is immobile
Whiskers contra-lateral to the awake hemisphere used to monitor position
Severely reduced REM sleep
Summer (Live on land)
Bilateral NREM and REM
No REM rebound during the immediate post-winter period
sleep properties of white crowned sparrow
Migrates between Alaska and California in the Spring and Autumn (>4,000 km).
Field observations suggest that during non migration the birds are diurnal.
During the migration they fly at night, but are still active during the day.
No apparent sleep deprivation effects.
Importantly, the birds show the same seasonal activity patterns when confined to the laboratory.
EEG recordings in frigatebirds
Measurements
Left and right EEG
Altitude and GPS
Evidence of uni- and bi- hemispheric sleep, as well as REM events, during flight.
Evidence that sleep serves a function
Numerous brain pathways to maintain sleep/redundancy in the system.
Serious physiological changes/death result from prolonged sleep deprivation of animals.
Sleep is ubiquitous among mammals, birds and reptiles; and probably exists in amphibians, fish and invertebrates.
Sleep has persisted in evolution even though it is apparently maladaptive with respect to other functions.
Accommodations are made to permit sleep in different environments and life styles.
