I had heard the proverb about a cat in a dream, but do cats, pigeons, fish, crows, cows, buffaloes and other animals also dream like humans?
It was once widely believed that the ability to dream was a special human trait. But a surprisingly wide variety of organisms can also be able to do this.
In a lab, a few young jumping spiders hang by a thread in a box overnight. Every now and then their legs twist and their spinnerets twitch. The retinas of their eyes move back and forth and this process is visible through their semi-transparent exoskeleton.
Daniela Rossler, a behavioral ecologist at the University of Konstanz in Germany, says that what these spiders are doing appears to be very similar to REM (rapid eye movement). During REM or REM (which stands for rapid eye movement), a sleeping animal’s eyes blink unpredictably, among other features.
REM occurs in humans when they have dreams, especially the most vivid dreams. This leads to an interesting question: If spiders have RAM processes during sleep, can dreams occur in their poppy seed-sized brains?
Rossler and his colleagues reported in 2022 about retinal spinner spiders. While training the cameras on 34 spiders, they found that they went through a period of rumination every 17 minutes.
In such a short visit, the brightness of his eyes was special. This was not the case when these jumping spiders moved, stretched their legs, adjusted their webs, or cleared themselves with a leg.
However, despite the periods of REM, the team has not yet been able to prove that the spiders are actually sleeping during this time. But if it turns out that she’s asleep and if it seems like REM is really REM, then dreaming could be one of the possibilities, according to Rossler.
They think it’s easy to imagine that jumping spiders, being among the most visual animals, can take advantage of their dreams.
Rossler isn’t the only researcher pondering questions in animals that elude us. Scientists today are finding traces of REM sleep in more animals than ever before.
They have seen this in spiders, lizards, catfish, zebrafish, etc. Their increasing numbers have led some researchers to wonder if dreaming, once thought to be a human trait, is more widespread than it seems.
REM sleep usually has many other characteristics besides rapid eye movement. It also includes temporary muscle paralysis, intermittent body twitches, and increased mental activity, breathing, and heart rate.
It was first observed in sleeping infants in 1953, and then REM was identified in mammals such as cats, rats, horses, sheep, opossums, and armadillos.
Events in the brain during REM have been well observed, at least in humans. During periods of non-REM sleep, also known as quiet sleep, brain activity is synchronized.
Neurons simultaneously fire and then go silent, especially in the cortex of the brain, and this process creates a wave-like state known as slow waves. In contrast, during REM the brain shows electrical activity reminiscent of being awake.
However, REM sleep is not the same in all mammals. Echidnas, a marsupial mammal, exhibit features of both REM and non-REM sleep at the same time.
Reports of whales and dolphins suggest that they may not experience rime at all. Birds have REM sleep, which is caused by twitching of the beak and wings and relaxation of the muscles that hold the head.
Yet researchers are beginning to find similar sleep patterns in many branches of animals from different families.
For example, in 2012 researchers reported a sleep-like state in cuttlefish, as well as a curious ram-like behavior during which the animals periodically move their eyes rapidly, twitch their arms, and The colors of their bodies change.
The phenomenon was further investigated by behavioral biologist Teresa Iglesias during a fellowship at the Marine Biological Laboratory in Woods Hole, Massachusetts, collecting terabytes of video of half a dozen cuttlefish.
All six cuttlefish showed patterns of rim activity that repeated approximately every 30 minutes.
It showed his skin changing into different colors and patterns during his arm movements and eye movements.
In this, they were observed to camouflage and display attention-seeking signals, both of which are also displayed during their waking behaviors.
“Since the cephalopod’s brain directly controls the pattern of its skin, it suggests that the brain activity is getting a little weird,” says Iglesias.
He is now at the Okinawa Institute of Science and Technology in Japan.
Researchers have since observed a similar phenomenon in octopuses. If octopuses and cuttlefish dream, Iglesias says, “it invalidates the idea that we think humanity is so special.”
Researchers have observed REM or REM-like states by recording signals from electrodes in the brains of bearded dragons. And they have reported at least two sleep states in zebrafish based on the fish’s brain signature. In one of these states the neural activity is similar to that of the mammalian non-rhyme phase, i.e. quiescence. In another condition, the fish displayed the neural activity that occurs in its waking state. (Rapid eye movements were not observed in the case of fish.)
By observing the multiple stages of sleep in humans and its evolutionarily distant relatives, the authors suggested that different types of sleep arose millions of years ago. It is now known that bees can also flutter between two or more sleep states. Roundworms seem to have only one state of sleep.
The researchers, considering the possibility of dreaming in non-human animals, say that during REM-like sleep, the waking-like state in these creatures and the kind of behavior that suggests they are dreaming, such as pattern-shifting in cephalopods. Glimmering, or the spiders moving their tentacles. Sleep scientist Gianina Angurin at the Max Planck Institute for Biological Intelligence in Munich and the University Medicine Göttingen and her colleagues say that in pigeons, their pupil constricts similarly during sleep. are as they are during intercourse. This raises the question of whether the pigeons are dreaming or somehow re-experiencing what happened during their waking courtship, she says.
REM sleep has also been linked to the repetition of experiences in some animals. For example, when researchers looked at the brain electrical activity of sleeping mice that had previously undergone amnesia, they saw the firing of neurons in their brains that help with navigation and are associated with head direction, although While the mice were not moving their heads during sleep, they also observed activity in neurons associated with eye movements. This combination suggests that the mice may have had a dream-like experience in which they were scanning the environment, Angurin says.
With all these signs, it’s reasonable to infer that animals are dreaming, Angren says. “However, if we look at these reasons one by one, we find that none of them is sufficient to prove it definitively.”
Brain activity associated with replay, such as the RAM-like movement of rats undergoing amnesia, doesn’t just occur during sleep, Angurin says, but can also occur during planning or waking eye-dreaming. And the link between REM and dreaming is not absolute: Humans also dream in a non-REM state, and even when drugs are used to suppress REM sleep, participants in human studies have reported having long and strange dreams. Have a dream.
The biggest thing, Angurin says, is that people know they’re dreaming because they can report it. “But animals can’t report it, and that’s the biggest problem we have in the way of proving dreaming purely scientifically.”
Even what RAM is for is still debated. “No one knows what sleep is — non-REM or REM,” says neuroscientist Paul Shaw of Washington University in St. Louis. One of the most popular ideas is that RAM helps the brain create and reorganize memories. Other theories suggest that the REM supports brain development, helps develop the body’s motor system, maintains the systems or circuitry required for waking activities so that they do not decrease during sleep, or raises brain temperature.
If REM is found to be present in distant genera and species within the animal kingdom, it suggests that whatever role it plays could be very important, Iglesias says.
However, not all scientists are convinced that researchers are even looking at REM. Jerome Siegel, a neuroscientist who studies sleep at UCLA, says he’s simply adding to the notion that all animals have two sleep states, calling one of them REM. . Among them there are some animals like spiders which may not be sleeping. “Animals can do things that look the same, but they don’t necessarily have the same physiology,” he says.
Researchers continue to search for clues. Rossler’s team is trying to develop markers that can image spider brains. They can detect activation in areas that resemble tasks used in dreams.
Iglesias and others have implanted electrodes in the brains of cephalopods and captured their electrical activity during two sleep states. One is one that exhibits wake-like activity, and the other is a quiescent state, with mammalian-like neural signatures.
Ingurin has trained pigeons to sleep in an MRI machine and found that many of the brain areas that light up in human sleep are also activated in birds.
David M. Peña Guzman, a philosopher at San Francisco State University and author of When Animals Dream: The Hidden World of Animal Cognition, says that if cuttlefish and spiders and a wide variety of other pets dream, it is It raises interesting questions about their experience. Since dreams, he says, appear from the perspective of the dreamer, dreaming animals must have the ability to see the world from their own perspective.
He added that dreaming would also be an indication that they have imaginative abilities. ‘We want to think that humans are the only ones who can take a break from the world, we have to think a bit more about other animals,’ he says.