LECTURER: Good morning, everyone. In today's lecture, I'm going to talk about the role of sleep in humans and animals. Of all the biological processes in the animal kingdom, sleep is perhaps the most important. A human can survive for almost two weeks without eating, but did you know that one week without sleep can be fatal? It's even worse for animals, especially for those who must avoid predators. {[Without sleep, an animal is much less capable of avoiding an attack ][1]}-- {[this is the case for all animals, whether they are reptiles, mammals or fish.][2]} Let us look now at how different animals sleep, reasons for their ways of rest, and the potential problems they might encounter.

In marine life, sleep must be balanced with breathing. {[For example, the dolphin must float to the surface as it sleeps in order to breathe][3]}. Like other large sea mammals, they keep one eye open and one half of the brain awake at all times to maintain some amount of consciousness required to breathe and to watch out for possible threats. They sleep with only one brain hemisphere in slow-wave sleep.

{[Birds also have unusual sleeping patterns, mostly due to being constantly on edge in the presence of numerous predators.][4]} They usually sleep quite lightly -for example, Swainson's Thrush, also called Olive-backed Thrush, is a medium-sized thrush that takes hundreds of naps during the day, each of which lasts just a few seconds. While migrating, migratory birds tend to function well on micronaps.

Horses, on the other hand, do most of their sleeping standing up. Scientists think that horses develop their habit of sleeping upright as a defense mechanism, a way of protecting themselves against predators, and a standing position keeps a horse in a constant state of readiness to race away if danger should approach.

Also, horses do occasionally take short naps lying down. {[Horses are heavy animals with big muscles, but their bones are surprisingly delicate,][5]} so lying in one position for a long time could well injure a horse. {[Just like humans, animals can also have sleeping problems][6]}. Dr. John Hedricks and Adrian Morrison from the School of Veterinary Medicine, University of Pennsylvania in Philadelphia, determined that certain diseases were primarily associated with the sleep states in animals. In their research they emphasised that because so much in this area still remains unclear, animal models were very important for studies of sleep disorders. The physiology of sleep in animals is similar to that of humans.

But why do we humans sleep? {[Researchers and scientists believe it helps us organise our memories of the day ][7]}-- that sleep acts as a kind of filing system for the brain. Without it, our thoughts become disorderly and confused, which leads to increased likelihood of accidents and a tendency to say and do bizarre things. {[Researchers also believe that sleep plays a key role in learning][8]}. We sleep so that the brain can integrate new knowledge and form new associations. {[Because of the similar sleeping pattern to that of humans, rats are often studied in order to increase our knowledge of human physiology.][9]} In one study, rats were kept awake for almost two weeks, and their behavior was observed. Researchers found the sleep-deprived rats could hardly remember anything of what they had been taught that day. For example, one rat had been taught to recognise pictures of various Parisian landmarks in order to receive food -- pressing a button below a picture of the Louvre would result in food being released and so forth. However, when deprived of sleep, they would press buttons seemingly at random.

In addition to rats, the fruit fly, a small insect that feeds and breeds on spoiled fruit, also has been used as a model organism and thousands of scientists around the world work on it. But why was the fruit fly chosen to be studied? It was for practical reasons. The most important one is that the relationship between fly and human genes is so close that the sequences of newly discovered human genes, including genes that show a susceptibility, can often be matched against their fly counterparts. This provides an indication of the function of the human gene and could help in the development of effective drugs to help people with sleeping disorders. {[Therefore, many scientists today choose to study the genetic structure of the fruit fly,][10]} which could make a particularly important contribution to the understanding of developmental processes in humans.

In conclusion, sleep is a necessary part of life not just for humans, but for the entire animal kingdom. Now, I'd be happy to answer any questions you may have...

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