Fruit Flies, Octopus, birds and humans do not seem to have much in common. Some live on land, others are aquatic. Some fly, while others are terrestrial. Some are vertebrates, others have no spine. These creatures evolved separately and their common ancestors lie far back in the evolutionary chain. But they can share one key feature: they dream.
Almost all creatures sleep, although there is some debate as to whether unicellular organisms such as the paramecium do. But no one really knows Because. For years, researchers have been confronted with theories that sleep aids memory, growth, and learning, and it’s clear that humans need sleep to function properly, but there’s little that s ‘understand well. “Sleep is that big black box,” says Marcos Frank, a neuroscientist at Washington State University. Frank compares sleep to a mysterious organ: it clearly exists and is vital to animal health, but its exact function and the mechanisms that control it are still unknown.
It is even more puzzling that some species appear to have only a state of sleep, during which their brains are relatively silent, while others appear to experience two types, a quiet phase and an active state. In humans, the period in which the brain lights up with activity is called rapid eye movement sleep (REM). It’s when we dream and when we’re hardest to wake up.
For a long time, scientists had not observed this phase of deeper active sleep in amphibians or reptiles. Until recently, the theory was that it evolved later in history, through an ancestor shared by birds and animals. But in 2016 there was an active sleep in lizards. Then, in 2019, the condition was described with sepia and this March a team of scientists from Brazil published a paper in iScience identifying it in the octopuses. Cephalopods like these eons evolved before the appearance of creatures that would have shared a lineage with both birds and humans. “There’s no way there’s a common ancestor,” Frank says. Now scientists are wondering if this sleep state is more common than they initially realized or if it developed in different species at different times, the way wings and flight arose separately in insects, bats and birds. , a phenomenon called convergent evolution.
Understanding what selective pressures caused this adaptation and preserving the genes that encode it could help scientists understand what function sleep serves for the central nervous system and why it is important to sleep. “What does sleep do for animals?” asks Sidarta Ribeiro, co-author of the newspaper and director of the Brain Institute at the Federal University of Rio Grande do Norte.
The first step in studying how animals sleep is to find out when they sleep, in fact. This is more complicated than it sounds. “Imagine you’re on Mars and you’ve found an organism,” Frank says. “How would you know if he was sleeping or not?”
For mammals, scientists could implant electrodes in the brain to track how they are firing their neurons. But octopuses have a very distributed central nervous system. Instead of concentrating control of their nervous system on one brain, they have eight lymph nodes in their arms that often act independently.
Instead of using an invasive method such as connecting probes to determine the sleep states of octopuses, scientists at the Ribeiro Institute studied some of their behavioral characteristics. Sylvia Medeiros, a graduate student and lead author of the study, tested the excitement thresholds of the animals. Three of the four octopuses in the lab received a visual stimulus: a video of moving crabs. One obtained a vibratory stimulus, in the form of a small light on his tank. Medeiros wanted to see how quickly they responded to stimuli when they were awake. He then tested them when they appeared inactive and measured response rates. Slower reactions meant they slept deeper.