A dog howls pitifully in his sleep and wakes up with a start. The octopus suddenly changes color during night sleep, just as it does to camouflage itself while awake. A spider falling asleep curls its legs and its retinas move back and forth. The lion growls menacingly even though he is fast asleep. For centuries, the ability to dream was thought to be a uniquely human trait.. Now, Most scientists believe this is not the case and a comprehensive list Other species also dream.
“Sleep and sleep-like states exist throughout the animal kingdom, and recent studies convincingly show Sleep-like states in arthropods, nematodes, and even cnidarians“. Constance is the first sentence of a study conducted by scientists from Harvard and Florence universities and the Max Planck Institute for Animal Behavior and published in the ‘Proceedings of the National Academy of Sciences’ (PNAS).
However, the existence of different sleep stages among taxa is still unclear. Especially sleep study rapid eye movements (REM) The researchers admit that research is still largely focused on terrestrial vertebrates, particularly mammals and birds.
“The most obvious indicator of REM sleep is eye movement. However, mobile eyes “It evolved only in a limited number of lineages (an adaptation not particularly found in insects and most terrestrial arthropods), which limits comparisons between species,” the study emphasizes.
The authors argue that spiders from the Salticidae (jumping) family mobile retina tubes It allows them to direct their gaze and in newborn babies, these movements can be directly observed through their temporarily translucent exoskeletons.
animals with imagination
Researchers a This is a condition very similar to REM sleep in spiders.: “Periodic attacks of retinal movements during night rest with limb spasms and stereotypic leg-curling behavior.”
retinal movement segments those observed were “consistent, including regular durations and intervals, both of which increased throughout the night.”
The fact that these characteristic REM sleep-like behaviors exist in a highly visual and highly divergent lineage such as these spiders “further challenges our understanding of this sleep state,” according to the researchers.
Dreaming probably indicates the existence of an imaginative capacity in animals
Comparisons between such different origins raise important questions and answers about the visual brain. Origin, evolution and function of REM sleep. One of the most interesting questions concerns the fact that dreaming probably implies the existence of something. imagination in animals and faculty see the world from your perspective.
Most dreams in humans occur during the REM phase.. The question is whether spiders also dream, given that they have REM sleep. Other researchers are conducting similar studies on species such as lizards, cuttlefish or zebrafish. And in all of them, a phase occurs that is almost identical to human REM.
REM sleep is also characterized by rapid eye movementswith temporary paralysis of skeletal muscles, periodic body contractions And increases in brain activity, breathing, and heart rate.
It is not known exactly what the REM phase does. Scientists believe that it participates in the memory and learning process. May help the brain Creating and rearranging memorieseven to maintain its temperature.
Zebrafish and bearded dragons
In a healthy young adult REM sleep takes up approximately 25% of rest time. REM sleep was first observed in sleeping babies in 1953 and was soon identified in other mammals such as primates, cats, mice, horses, sheep, pigs, and armadillos.
Scientists suspect that octopuses and squids, for example, dream
For example, scientists suspect that: octopuses And squid They dream because, while they sleep, they experience different states similar to humans’ REM: their arms and eyes shake, their breathing rate accelerates, and they change color, as if they are responding to some kind of vision or dream image. REM-like phases have also been observed. birdsinside zebrafish And bearded dragons.
Another example: A team of German scientists found that their students pigeons They contract during REM, just like during dating, which makes them wonder if they are dreaming or somehow “re-experiencing what happened while they were awake.”
Given that such evolutionarily distant species have different sleep stages, scientists suggest they arose hundreds of millions of years ago.
All these signals also lead the study’s authors to assume that animals are dreaming.. However, they emphasize that such experiments should be continued because they have not yet been scientifically proven.
As a last resort, People know they are dreaming and can report it, but animals do not.. This is the biggest problem researchers face in detecting the existence of dreaming nonhuman animals in a completely scientific and robust way.
In fact, there are scientists (a minority) who argue that what these researchers see in non-human animals is not REM sleep, although it may seem that way.
Reference work: https://www.pnas.org/doi/10.1073/pnas.2204754119
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