Sleep in different animal species
Sleep in mammals, including man, does not differ from species to species in terms of quality. We can even see in birds the cyclical alternating of periods of NREM sleep with brief periods of REM sleep.
There are some particularly interesting differences between the sleep of land mammals and the sleep of acquatic mammals. For example, dolphins and seals can sleep with only half their brain in an acquatic environment. The partial presence of waking activity allows the animals to keep a constant check on their breathing.
The structure of sleep becomes progressively less complex as we move down the zoological scale, until it is reduced to the simple alternation of periods of activity and rest, as recently observed in flies (Fig. 3).
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