Animals still sleep at night even without the brain

Scientists first discovered jellyfish without brains and the central nervous system also slept at night.

American scientists first observed jellyfish, an animal without the brain and central nervous system, also slept at night, UPI reported on Sept. 21. The new finding helps scientists take a step forward in finding a solution to the question "Do all animals sleep?".

According to the study, all vertebrate species sleep. However, scientists cannot confirm whether sleep behavior is common in invertebrates. Some previous studies show that fruit flies and roundworms also sleep, while more primitive organisms such as sponges or jellyfish are still a mystery.

Cassiopea jellyfish sleeps at night.(Video: Caltech).

Researcher Paul Sternberg and colleagues at the Howard Hughes Institute of Medicine at the California Institute of Technology conducted an observation of the upside-down jellyfish called Cassiopea . This jellyfish has little movement, preferring to live in warm and shallow waters like mudflats.

Cassiopea looks like an upside-down cauliflower or mushroom, the round body part beneath it and the tentacles pointing up. They move in a steady rhythm, similar to other jellyfish. The team wanted to find out if these jellyfish were constantly moving.

"We came at night and used a video camera , " said Ravi Nath, a member of the research team. They watched the jellyfish in the tank for a few days and discovered, their thrust was slower than at night. However, the jellyfish start to return quickly when scientists release food into the tank.

They also placed jellyfish on a hanging mesh background so they could lower the net from below. During the day, when the grid is down, jellyfish quickly swim to the bottom of the tank. However, their reactions become much slower at night. This reinforces the conclusion, jellyfish also sleep at night.

Jellyfish upside down Cassiopea.

Researchers also found that jellyfish will move less during the day if their sleep is interrupted at night."After sleeping, they will return to normal , " Nath said.

Stemberg wants to conduct further research. He hopes future research will help answer complex problems such as animals that need neurons or many cells to sleep.