For those people who like to stay up late every night, here's a thought: If brainless jellyfish need to sleep, then you probably need it too.
Three graduate students from the California Institute of Technology have proven that at least one group of jellyfish do need to sleep, which is the first time that it has been confirmed for animals without a brain.
Brainless Jellyfish Also Need Sleep
Jellyfish are creatures with a diffuse nerve net, which is a system of neurons that are distributed throughout organisms instead of being organized within a brain. However, even without a brain, a primitive upside-down genus of jellyfish known as Cassiopea were found to exhibit sleep-like behavior similar to what can be seen in humans at night.
The quest to determine whether jellyfish sleep started when Claire Bedbrook overhead fellow PhD students Michael Abrams and Ravi Nath arguing whether the creatures need to sleep. Bedbrook said that jellyfish do not, as sleep has been associated with memory consolidation and REM cycles within the brain. Without a brain, jellyfish should not be needing sleep at all.
It took months of work, but the trio has finally published a paper on the matter in the Current Biology. The study changed Bedbrook's mind: jellyfish apparently do sleep, or at least the Cassiopea does.
The Cassiopea, which live in the Pacific and Atlantic oceans, do not swim around much and are content with staying on the ocean floor where they pulsate. The researchers set up cameras in a tank to record the pulsating activity of the jellyfish over 24 hours, and they found that in certain times at night, their pulsating rate decreases to 39 times per minute, compared to 58 times per minute in the day. The jellyfish also displayed decreased response time to stimuli while in their sleeping state and showed negative reactions to states of sleep deprivation.
Jellyfish Sleep Too: Why Does This Matter?
So the research showed that brainless jellyfish also sleep. So what?
The results of the study showed that sleeping is deeply rooted in the biology of the Earth, as a behavior that has been present even back when organisms did not yet have brains like the jellyfish.
With jellyfish also needing it, further questions are raised on the purpose of sleep. If jellyfish sleep without brains, does this mean that the requirement to sleep is caused by the presence of neurons? And if a creature without a brain has shown that it needs to sleep, do other living organisms such as plants also sleep?
Understanding why jellyfish need to sleep could also lead to the long-sought answer to the question of why humans also need it, when we can spend our valuable time doing other things instead such as binge watching on Netflix and playing video games.