Lecture 11 - Function of Sleep - Part 1 Flashcards
“If sleep does not serve an absolutely vital function, it was the biggest mistake the evolutionary process has ever made.”
Allan Rechstschaffen
What are some of the ways that the function of sleep can be investigated?
- Disrupt sleep.
- Modify function factors and see how this affects sleep.
In 1989 Rechtschaffen and colleagues performed experiments on rats where they were unable to go to sleep. They had one control rat who could sleep. One rat who could not sleep.
What were some of the findings from this study?
After 10-20 days all sleep-deprived rats died.
However, the rats died from lots of different reasons, such as organ failure, infection, and hypothermia.
Rats lived longer without food than they did without sleep.
Rats that were only deprived on REM sleep lived for about 45 days, but still died.
What were the physiological changes observed in the rats who were sleep-deprived?
Scrawny, mangy.
Oily fur.
Increased food intake, decreased weight.
Did the rats recover when they were allowed to sleep?
Yes.
The sleep-deprived rats steadily lost weight, whilst simultaneously steadily increasing food intake.
How was this interpreted?
This made researchers think that sleep served a ‘energy reservation’ function.
Sleep is thought to be an energy-saving process. This was thought to be because when we are asleep we move less and therefore our energy expenditure is less. However, it could also have been due to a circadian rhythm for metabolism.
What was one experiment that looked into this and what did they find?
Individuals got into bed at the same time. One was allowed to go to sleep straight away. The other was only allowed to go to sleep after 3 hours. The other was only allowed to go to sleep after 6 hours.
When each individual went to sleep their energy expenditure (as mesured my oxygen consumption) dropped. However, the metabolism of the participants who did not go to sleep straight away was steadily decreasing even when they were awake. Suggests that metabolism functions on a circadian rhythm.
Does energy expenditure differ between the different sleep stages?
No.
What phase of sleep appears to impacted by fasting?
Stage 3/4 sleep (slow wave sleep, delta waves).
What are some criticisms of sleep being an energy-conserving process?
The amount of energy conserved via sleeping is only equivalent to about 2 apples. It would be more efficient just to eat a bit more than to spend 1/3 of our lives sleeping, from an evolutionary perspective.
We eat to keep our body warm. When we go to sleep we actively reduce our temperature. This seems counterproductive.
What are some of the ways we can measure sleep in animals and insects?
Prolonged inactivity.
Postures of sleep.
Reduced responsiveness.
It is thought that REM sleep has evolved more than once. Why?
Placentals, marsupials, and montrenes evolved from an ancestor that evolved from a common ancestor that birds, crocodiles and lizards also evolved from. The former all have REM sleep, but the latter do not except birds. This has lead to researchers thinking that REM sleep may have evolved more than once.
Mammals that are larger tend to sleep less than mammals that are smaller.
T/F
True.
e.g giraffe sleeps 2 hours a day, whereas a little brown bat sleeps 20 hours a day.
This there a negative relationship between number of predators and amount of sleep?
Yes.
If an animal has more predators it is more likely to sleep more of the day. This is thought to occur because when an animal is asleep it is out of sight from predators, often.
What is the Sleep Immobility Hypothesis?
This theory states that we have a rest-activity circadian pattern with our behaviour that helps survival, such that we rest during periods where we might be in more danger if we were active, such as during the night. To aid with resting and not being active, sleep evolved to make us immobile.
