MadSci Network: Zoology

Re: dolphins and sleep

Area: Zoology
Posted By: Nick Bourbaki, Collective Enigma Elucidator
Date: Fri Jan 3 03:39:50 1997
Message ID: 845582164.Zo

Hi -

Dolphin's don't 'sleep' in the sense that we do. They do however have conscious control over their breathing like we do, in which case loosing consciousness in the ocean could be quite deadly. Research into this area suggests dolphins 'sleep' one cerebral hemisphere at a time, meaning they close down one half of their brain for a little while, letting the other half take care of the necessary functions such as breathing. I do this all the time; it's quite effective for getting through graduate classes..

I'll copy in some explanations from the Dolphin FAQ, and the FAQ for the USENET group alt.animals.dolphin that give specifics.



From the Dolphin FAQ
How do dolphins sleep?

Dolphins sleep only with one half of their brain at a time ! Remember Dolphins are conscious breathers. Should they sleep and go unconscious as we do they would simply suffocate or drown. Sleeping Dolphins can be seen as resting, floating at the surface, with one eye open. After a time, they will close the one eye and open the other one. They alternate like this throughout their entire nap.

From the FAQ for alt.animals.dolphin
2.1 - How do dolphins sleep?

Dolphins have to be conscious to breath. This means that they cannot go into a full deep sleep, because then they would suffocate. Dolphins have "solved" that by letting one half of their brain sleep at a time. This has been determined by doing EEG studies on dolphins. Dolphins sleep about 8 hours a day in this fashion. REM (Rapid Eye Movement) sleep, usually associated with dreaming has been recorded only very rarely. Some scientists claim dolphins do not have REM sleep at all.

A dolphin's behavior when sleeping/resting depends on the circumstances and possibly on individual preferences. They can either:

  S.H Ridgway (1990)
    The Central Nervous System of the Bottlenose Dolphin, 
    in S. Leatherwood and R.R. Reeves: The Bottlenose Dolphin, pp. 69-97, 
    Academic Press

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