sleep

From: Pieter Arend Folkens (animalbytes@earthlink.net)
Date: Mon May 29 2000 - 03:50:34 EDT


> Our question is how do whales sleep, or do they? Please respond my
>niece and I have been wondering for quite a long time.
> Sincerely
> Farrah Dawn

Some fifty years ago, John Lilly was researching the effects of
psycotrophic drugs on large brains. He chose dolphins before experimenting
on humans. During the early experiments, he anesthetized his subjects, but
all of them died. He figured out that dolphins were conscious breathers,
that is, they had to decide when to take a breath. (Most animals, including
humans, are automatic breathers.) The conclusion: dolphins could not be
anesthetized.

This lead to anscillary studies on dolphin (and by extension, cetacean)
sleep. Dolphins have a bicameral (split) brain. Simply put, they go into
rest stages in which one side goes deeper into sort of a sleep mode, while
the other side, though still restfull, stays awake to breathe. Lilly
observed that when the left side was in the deep rest mode, the dolphin
swam in a counterclockwise direction, then, after about 30 to 45 minutes,
the animal switched directions, ostensibly as the brain swiched which side
was in the deeper rest mode.

Another thought regarding sleep in cetaceans is that they are bouyant
compared with terrestrial animals, most of which need to stand for much of
the day, balancing against gravity. The simple act of balancing is more
tiring than floating. The notion goes that terrestrial animals need more
sleep than ocean-going mammals.

Also, deep diving seals (like the elephant seal) go into a deep sleep mode
as they move between the surface and the ocean floor. The cycle goes
somewhat like this: they breathe at the surface, taking on a store of
oxygen in the muscle tissues. They then dive, and on the way down, go into
a moving sleep mode in which much of their body shuts down. They wake up
near the bottom, feed for a while, then head back to the surface while in
another sleep mode. Although not yet fully understood, the diving
physiology of some deep-diving cetaceans may also follow this "sleep
diving" kind of restfull behavior. However, some studies of deep-diving
sperm whales suggest sperm whales are socially active during a dive.

Cheers,

Pieter Folkens
Alaska Whale Foundation

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