The ancestors of the cetaceans, like the dolphins, were mammals that evolved on land.55 million years ago, those animals returned to aquatic life, even as mammals, so they developed a special respiratory strategy.
All terrestrial mammals have an autonomous respiration, it is That is, it is not consciously controlled, unlike aquatic mammals, specifically the cetaceans, who have a conscious breath and decide when they need air.Even when they are resting on the surface, they only breathe about three times per minute, with very rapid breaths and deep, which fill the lungs up to 80 or 90 percent of their capacity.
Because of their need to swim and have to perform this type of breathing, it is not surprising that many people have wondered how they get dolphins sleep in water.In this article of Animals and Pets Online, we will discover how dolphins breathe when they sleep or what the dream of these animals is like.
What is sleep?
To understand how dolphins sleep before we must know what the sleep and wake process is like in mammals.The waking state and the sleeping state can be easily distinguished at the physiological and behavioral level.
The sleep process has two phases: slow or non-REM wave sleep and fast or REM wave sleep.While awake, the encephalographic activity is out of sync, shows low amplitude but high frequency waves, unlike of this activity during the sleep process that synchronizes, increases the amplitude of the waves and lowers their frequency.
During the non-REM phase, the muscular activity of the body gradually decreases, until it is canceled in the phase REM, so that muscular atony is produced from the neck down (there are no responses from the muscles of the body).Also, in the REM phase rapid eye movements occur and the body temperature drops.
Then How do dolphins sleep?
Unihemispheric dream
It was in the decade of the 70s, when a group of researchers from the USSR, discovered how dolphins sleep.Although there are two phases during sleep, dolphins only know the existence of one of them, the non-REM and is presented in a unihemispheric way, this means that, when one dolphin sleeps, it only "disconnects" one of the hemispheres of the brain, while the other continues its waking activity or, to put it another way.In this way, one hemisphere of the brain is out of sync (awake) and the other is synchronized (asleep).
Moving from one awake state to another asleep happens gradually, that is, while one hemisphere is falling asleep the other it wakes up, so we can find intermediate states in which a hemisphere is half asleep half alert.
The REM phase of sleep has not been identified in dolphins but in some cetaceans and, surprisingly, it is not shows unihemispherically, but throughout the brain.
Dolphins sleep with one eye open
The unihemispheric dream in dolphins seems to occur especially during the night, in the second half of the day and at dusk.The studies carried out show that both hemispheres rest the same number of hours.
Having this type of dream leads to a series of behaviors that allow the dolphin to continue interacting with the outside.For example, one of these behaviors is that dolphins sleep with one eye open.When the hemisphere The right brain enters the non-REM phase, the left eye closes and, when it is the left hemisphere that sleeps, the right eye closes.
While a dolphin sleeps, you can continue doing all the activities You want to rest on the surface of the water, breathe, swim or communicate.
Why do dolphins have no unihemispheric REM phase?
We might think that dolphins have no REM phase because during this phase the body goes into muscular atony and the dolphin could sink, but the scientists are not so clear.if there was a unihemispheric REM dream, only half of the body would enter atonia and there could be compensatory mechanisms to continue interacting with the environment.
The current hypothesis that more followers have is that a dolphin could not have a unihemispheric REM dream because he might not know how to differentiate between dreams and reality.Half of his brain would be analyzing information from the real world and the other half, information from the dream world.If this happened they would be easy prey for predators.
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Bibliography
- Goley, PD1999.Behavioral aspects of sleep in pacific white ‐ sided dolphins (lagenorhynchus obliquidens).Marine mammal science, 15 (4): 1054-1064.
- Howard, RS, Finneran, JJ,&Ridgway, SH2006.Bispectral Index Monitoring of Unihemispheric Effects in Dolphin s.Technology, Computing, and Simulation, 103 (3): 626-632.
- Toledo, V.,&Ross, A.2004.Unihemispheric sound in dolphins.TecnoVet, 10 (3): 3-7.
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