Researchers of a new study recently identified a state akin to sleep in a tiny, freshwater animal, also known as "hydra," which has simple anatomy and doesn't have a brain.
Such a finding, as reported by Live Science, appears to oppose the common knowledge that the brain needs sleep to function properly. It turns out, based on what the researchers discovered, one does not require a brain to sleep.
According to Japan-based Kyushu University assistant professor Taichi Itoh, they currently have "strong evidence that animals must have acquired" the necessity to sleep before they acquired a brain.
The said research, which Science Advances recently published, has consequences for understanding the reason for the necessity for sleep evolved.
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Based on the new study and past reports on jellyfish, scientists can say that ‘sleep evolution is independent of brain evolution.’
Sleep Evolution, Independent of Brain Evolution
Sleep, the study indicates, is almost universal among animals, seen in human beings and all mammals, even in insects and roundworms.
Nevertheless, all the said creatures have some sort of central nervous system or brain, and so, researchers did not know if the evolution of sleep preceded that of brains or the other way around.
Jellyfish, a relative species of hydras that don't have a brain, as well, have exhibited a behavior akin to sleep. Nonetheless, this new finding contributes to such findings by presenting that hydras do not just sleep but react as well to the similar molecules that control sleep in humans, as well as the other advanced animals.
Itoh explained, based on their findings and past reports on jellyfish, they can say that "sleep evolution is independent of brain evolution."
Hydras Had Cycles of Active and Sleep States
For this research, the study authors essentially used a hydra cam, a video-recording system, to monitor the movement of the hydras and identify if they "had entered a sleeplike state," or a state of decreased movement that could be interrupted through the use of a flashlight.
The scientists discovered that hydras had cycles of active and sleep states that lasted roughly four hours each. Additionally, interrupting the sleep state of hydras, along with changes in temperature or vibrations, led to indications of sleep deprivations. For instance, they needed to sleep afterward and exhibited reduced cell growth.
The study investigators exposed the hydras, too, to chemicals engaged in sleep control in humans, which includes melatonin and neurotransmitter, or the so-called GABA brain chemical. Essentially, exposure to the two chemicals increased sleep in the said creatures.
Nevertheless, the chemical dopamine, which comprises a stimulating impact on many animals, rather promoted sleep in hydras.
Itoh said, it appears that while "some sleep mechanisms seem to have been conserved," others may have substituted function during the brain's evolution.
Researchers also discovered that when they had the hydras deprived of their so-called "shuteye," changes were observed in terms of expression of over 200 genes, which include some that are engaged in the regulation of sleep in other animals.
In general, these experiments offer strong evidence that "animals acquired sleep-related mechanisms" prior to the evolutional progress of the central nervous system that a lot of these mechanisms "were conserved as brains evolved," explained Itoh.
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