Biology – reptiles and spiders in the sleep laboratory

Healthy sleep is incredibly important for our immune system and our mental and emotional balance. What is particularly exciting from a research perspective is REM sleep as the last phase of a sleep cycle, where REM stands for “Rapid Eye Movement”. This is the phase in which we as humans dream.

Sleep is described in all large animal groups from fish to humans – including worms, jellyfish, insects and cephalopods. However, sleep research in animals is a fairly young scientific discipline and REM research in animals is only just beginning. However, we already know that marine mammals such as dolphins and orcas lack the REM phase. Because they have to come up regularly to breathe, only one half of the brain is switched off during sleep while the other remains wide awake.

According to a publication from June 2023, researchers at the Ruhr University Bochum (RUB) observed and recorded the sleeping and waking states of 15 pigeons using infrared video cameras and functional magnetic resonance imaging. “During the REM phases, areas of the brain that are responsible for processing visual stimuli were particularly active, including areas that analyze how the pigeon’s surroundings move during flight,” reports Mehdi Behroozi from the biopsychology team in one Article on the RUB website and adds: “Based on these observations, we suspect that birds, like us humans, dream in REM phases and perhaps even experience flight sequences.”

REM sleep may have existed as early as 320 million years ago.

Eight years ago, Gilles Laurent’s research group at the Max Planck Institute for Brain Research discovered a REM-like state in the bearded dragon, a reptile. This discovery suggested that REM sleep could be a common feature of all living things and may have existed in their common ancestors 320 million years ago, a November 2024 report said Article about reptiles on the Max Planck Society website.

In 2012, researchers reported a sleep-like state and REM-like behavior in octopuses: At regular intervals, the animals quickly moved their eyes, twitched their arms, and changed the color of their bodies. Fascinated by these observations, behavioral biologist Teresa Iglesias at the Marine Biological Laboratory in Massachusetts further investigated this phenomenon by placing half a dozen squid under long-term video surveillance. Repetitive REM-like activities such as arm movements, eye movements and skin color changes could be seen approximately every 30 minutes. This indicates a type of REM sleep, Iglesias told Ars Technica’s Knowable Magazine. Research colleagues observed something similar with octopuses. But when octopuses and squids dream, “it somehow pushes the boundaries of what we think of humanity as unique,” said Iglesias.

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Daniela Rössler, behavioral ecologist at the University of Konstanz, studies the sleeping behavior of spiders. She has already been able to observe sleep and REM-like phases in jumping spiders and the garden spider through experiments. Thanks to an Emmy Noether grant of around 1.5 million euros, Rössler will start the research group “Sleeping with eight eyes open: morphology, function, ecology and development of sleep in spiders”. “We will focus on studying spider sleep in a comparative evolutionary framework,” Rössler said happily on her website in June.

In animals, brain waves and behavior during sleep can be measured and documented and the data can be used to demonstrate a phase that is at least REM-like. But whether animals actually dream, and if so what, is beyond research.

But no rule without exception. Female gorilla Koko, who was born at the San Francisco Zoo, learned American Sign Language and deaf-mute language and is said to have told her keepers about frightening dreams. But this is not scientifically proven.

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