Sleep Without a Brain

Sleep Without a Brain

Cornell Current
Science

Sabrina Chow ‘25

Sleep is a non-negotiable part of being human. Neglecting sleep leads to grogginess, short fuses, and generally a bad time. Still, nearly everyone wishes that they could have more time in the day. Why should humans be limited by sleep? Recent studies have shown that even animals without brains have a need for sleep, suggesting that the demand for sleep is deeply rooted in our evolution. 

Sleep is the temporary stillness and loss of consciousness that humans (and many other organisms) go through each night. There are two parts to sleep: rapid eye movement (REM) sleep and non-REM sleep. Non-REM sleep makes up the majority of the night, but many studies focus on REM sleep because this phase is responsible for dreams and memory consolidation. The intricacies of sleep are still being worked out, but it is clear that sleep plays a major role in keeping organisms healthy. Sleep is essential for maintaining homeostasis, which is the balance of the body’s internal workings. For creatures with a brain, sleep helps with sorting out memories and getting rid of an accumulation of beta-amyloid protein waste in the brain. Furthermore, sleep is a method of recovery following physical and mental exercise. When humans are deprived of sleep, it has been found that they struggle with performing the normal simple functions. The only way to fix a lack of sleep is with sleep, and even short periods of sleep are beneficial. 

Over the past few years, researchers have begun to examine animals without brains. Their results have revealed that even these creatures need sleep. For example, jellyfish and hydra do not have brains, but they still exhibit a distinct stage of rest that aligns with the twenty-four hour day cycle. A study by graduate students at the California Institute of Technology shows that Cassiopea jellyfish pulse and react to stimuli much slower in the dark. When the jellyfish are deprived of this resting period, they are less active during the next day, seemingly needing to make up for the loss of sleep. Similarly, the hydra species Hydra vulgaris has been observed to be less active in the dark. Although Hydra does not follow the same twenty-four hour circadian rhythm, it still demonstrates a distinct sleep-like state. This may indicate that Hydra’s sleep-like state is an example of the earliest iteration of sleep. Even sponges, which have no nerves or sensory cells, have been shown to detect changes in light and act more during the day. A study looking at the sponge Amphimedon queenslandica found many of the genes that are responsible for the circadian clock in eumetazoans and that some of those genes turn on and off with the day cycle. 

Even though sleep makes up such a large part of daily life, much of the science around it is still in development. The evidence that even animals without brains need sleep suggests that sleep is even more important than previously assumed. As sleep gets increasingly neglected today in favor of longer work days, these advances in the study of sleep emphasize the key role that sleep plays in allowing all kinds of organisms, including humans, to perform at their best. Hopefully, this discovery will inspire further research-- from the evolutionary purpose of rest to the best conditions for sleep. 


Sources:

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