Lecture 13 function of sleep

Question 1

What are some things to consider when studying sleep

Answer 1

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

Question 2

What is the result of total sleep deprivation in the rat

Answer 2

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

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

Question 3

What are symptoms of total sleep deprivation in rats

Answer 3

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

Question 4

What was the effect of total sleep deprivation on energy expenditure, body weight and food intake in rats

Answer 4

Both food intake and energy expenditure went up and weight went down, Total sleep deprivation shows greater effect than control

Question 5

describe the strong and weak form of energy conservation theory

Answer 5

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

Question 6

What is the pattern of energy expenditure in a day and what is it related to

Answer 6

oxygen intake drop during sleep, independent of circadian rhythm as shown by study

o2 consumption used as an indicator of energy expenditure

Question 7

describe a study in support of energy conservatio ntheory

Answer 7

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

Question 8

describe criticisms of energy conservation theory

Answer 8

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.

Question 9

how does sleep vary across species

Answer 9

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

Question 10

What is weird aobut monotremes’ sleep

Answer 10

they show a mix of sws and rem - sws with eye movement and rem atonia after rem started….

Question 11

describe phylogeny of sleep

Answer 11

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

Question 12

association between total daily sleep time and animals

Answer 12

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

Question 13

degree of enchephalisation and sleep

Answer 13

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

Question 14

what are the factors associated with sleep

Answer 14

number of predators, body size (also dependent on type of animal), brain size

Question 15

number of predators and sleep

Answer 15

Number of predators

Negatively related to amount of sleep

Question 16

describe immobility hypothesis

Answer 16

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.

Question 17

evidence and drawback of immobility hypothesis

Answer 17

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.

Question 18

some random conclusions of phylogenetic studies

Answer 18

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.

Question 19

Sleep Properties in the Cetaceans

Answer 19

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)

Question 20

Postpartum Sleep in Cetaceans

Answer 20

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

Question 21

sleep properties of fur seals

Answer 21

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

Question 22

sleep properties of white crowned sparrow

Answer 22

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.

Question 23

EEG recordings in frigatebirds

Answer 23

Measurements
Left and right EEG
Altitude and GPS

Evidence of uni- and bi- hemispheric sleep, as well as REM events, during flight.

Question 24

Evidence that sleep serves a function

Answer 24

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.