Bizarre Science: Do you need a brain to sleep?

Human sleep is defined by polysomnography: the movement of brain activity, eye movement, and muscle tone. However, as science progresses, varied research of sleep in other species has provided new definitions. When scientists began to inquire whether we needed a brain to sleep, they started investigating sleep schedules of creatures such as Hydra vulgaris  – a tubular body less than half an inch in length, without a nervous system, and brainless. Ketema Paul, a neuroscientist at the University of California Los Angeles said he “is one of those people who thought sleep was all about the brain” but with time, has considered this to be an “erroneous viewpoint.” 

Carolyn Smiths, a neuroscientist at the National Institute of Neurological Disorders and Stroke who has studied placozoans for more than 10 years, proposes sleep is not only for those who have brains. This notion has been exemplified via UV-light experiments on jellyfish and Hydra species. Taichi Itoh, a chronobiologist at Kyushu University, along with his colleagues observed how sensitive these species were to light, and found Hydras were less responsive in the dark, thus pointing toward their sleep states. Moreover, Michael Abrams and two other California Institute of Technology graduate students obtained sleeping activities from the Cassiopea jellyfish, claiming its motion declined from 60 pulses per minute to just 39 in the night. 

Scientists have also tried to monitor the amount of contractions species perform. The rhythmic contractions indicate their rest cycles, and in 2017, the genes in the sponge Amphimedon queenslandica were navigated. They were found to be responsible for carrying out circadian rhythms which turn on and off in the duration of 24 hours. This was enough evidence for Davide Poli, a graduate student, to prove these species’ have “behaviour[s] that can be approximated to sleep.” 

These research results have allowed scientists to discover profound sleeping functions, beyond letting the brain rest. Having a deeper understanding of the brain and cells controlling sleep is hoped to help people who suffer from illnesses such as insomnia, apnea and other sleeping disorders.

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Melody Chan

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May 2022
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