Spiders may dream and have REM-like sleep stages, just like humans
Dr. Daniela Rößler/Twitter
- A group of scientists has observed a REM sleep-like state in the spiders.
- According to researchers, spiders might be dreaming.
- Although the research does not show precisely what sleep state the spiders are in, the results are satisfactory.
Researchers have recently observed the REM sleep-like state of the jumping spiders.
Ecologist Daniela Roessler of the University of Konstanz and the Max Planck Institute of Animal Behavior in Germany is the lead author of a report on jumping spiders published in the journal PNAS. Roessler also shared the study findings and a video on Twitter:
While filming hanging jumping spiders at night, we noticed surprising things happening. Regular phases of curling up their legs and twitching in what seemed like uncontrolled movements. Reminding us a lot of sleeping dogs or cats, we asked: could this be REM sleep? 2/7 https://t.co/TdSjwg21hD— Dr. Daniela Rößler ? (@RoesslerDaniela) ) August 8, 2022
"Too wild you think? So did we. We followed up anyhow. Luckily, fresh spiderlings are translucent during the first week, giving us the unique opportunity to check out their retinas (they can’t move their “eyes”, but their retinas, which is extra cool)" added Dr. Daniela Roessler.
Although spiders cannot move their eyes like humans and some mammals, they can move their retinas. Therefore, by observing jumping spiders, the scientists observed the retinal movements of spiderlings as their cobwebs hang themselves with silk threads to rest at night. According to the research team's report, the spiderlings' retinal movement bouts were said to be consistent.
The scientists aren't ready to declare that jumping spiders are dreaming, but Roessler called the possibility "exhilarating." "We need to have a closer look at how universal REM sleep and REM-like behaviors might be across the animal kingdom," Roessler tweeted. "There are likely many things we can learn from this, since even in humans REM sleep is still a big mystery."
What is REM sleep?
Rapid eye movement sleep (REM sleep or REMS), the dreaming phase of sleep. It gets its name from the rapid movement of the eyes during this time. Rapid eye movement sleep is also called as paradoxical sleep or asynchronous sleep. REM sleep was first described by Dement and Kleitman in 1957. During REM sleep, the release of serotonin and norepinephrine is low, while the release of acetylcholine is dominant. The brain region that controls REM sleep is considered to be the midpoints of the brain stem. Although the duration of this sleep period varies from person to person, it lasts between 5-30 minutes and is repeated every 90-120 minutes. In a normal night's sleep, it is seen to be repeated 4-6 times.
Sleep and sleep-like states are present across the animal kingdom, with recent studies convincingly demonstrating sleep-like states in arthropods, nematodes, and even cnidarians. However, the existence of different sleep phases across taxa is as yet unclear. In particular, the study of rapid eye movement (REM) sleep is still largely centered on terrestrial vertebrates, particularly mammals and birds. The most salient indicator of REM sleep is the movement of eyes during this phase. Movable eyes, however, have evolved only in a limited number of lineages—an adaptation notably absent in insects and most terrestrial arthropods—restricting cross-species comparisons. Jumping spiders, however, possess movable retinal tubes to redirect gaze, and in newly emerged spiderlings, these movements can be directly observed through their temporarily translucent exoskeleton. Here, we report evidence for REM sleep–like state in a terrestrial invertebrate: periodic bouts of retinal movements coupled with limb twitching and stereotyped leg curling behaviors during nocturnal resting in a jumping spider. Observed retinal movement bouts were consistent, including regular durations and intervals, with both increasing over the course of the night. That these characteristic REM sleep–like behaviors exist in a highly visual, long-diverged lineage further challenges our understanding of this sleep state. Comparisons across such long-diverged lineages likely hold important questions and answers about the visual brain as well as the origin, evolution, and function of REM sleep.
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