MSGID: 1:317/3 649d08e8   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Octopus sleep is surprisingly similar to humans and contains a wake-like   
   stage    
      
     Date:   
         June 28, 2023   
     Source:   
         Okinawa Institute of Science and Technology (OIST) Graduate   
         University   
     Summary:   
         Researchers have closely examined the brain activity and skin   
         patterning in octopuses (Octopus laqueus) during active sleep   
         and discovered that it closely resembles neural activity and skin   
         patterning behavior seen when awake.   
      
      
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   When octopuses sleep, their quiet periods of slumber are punctuated by   
   short bursts of frenzied activity. Their arms and eyes twitch, their   
   breathing rate quickens, and their skin flashes with vibrant colors.   
      
   Now, researchers from the Okinawa Institute of Science and Technology   
   (OIST), in collaboration with the University of Washington, have closely   
   examined the brain activity and skin patterning in octopuses (Octopus   
   laqueus) during this active period of sleep and discovered that they   
   closely resemble neural activity and skin patterning behavior seen when   
   awake. Wake-like activity also occurs during rapid eye movement (REM)   
   sleep in mammals -- the phase in which most dreams occur.   
      
   The study, published 28 June inNature, highlights the remarkable   
   similarities between the sleeping behavior of octopuses and humans and   
   provides fascinating insights about the origin and function of sleep.   
      
   "All animals seem to show some form of sleep, even simple animals like   
   jellyfish and fruit flies. But for a long time, only vertebrates were   
   known to cycle between two different sleep stages," said senior author,   
   Professor Sam Reiter, who leads the Computational Neuroethology Unit   
   at OIST.   
      
   "The fact that two-stage sleep has independently evolved in distantly   
   related creatures, like octopuses, which have large but completely   
   different brain structures from vertebrates, suggests that possessing an   
   active, wake-like stage may be a general feature of complex cognition,"   
   said author Dr. Leenoy Meshulam, a statistical physicist at the University   
   of Washington, who helped design the research during her three month   
   stay at OIST as a guest of the Theoretical Sciences Visiting Program.   
      
   To begin, the scientists checked whether the octopuses were truly asleep   
   during this active period. They tested how the octopuses responded to a   
   physical stimulus and found that when in both the quiet and active stage   
   of sleep, the octopuses required stronger stimulation before reacting,   
   compared to when they were awake. The team also discovered that if they   
   prevented the octopuses from sleeping, or disrupted them during the   
   active phase of sleep, the octopuses later entered active sleep sooner   
   and more frequently.   
      
   "This compensatory behavior nails down the active stage as being an   
   essential stage of sleep that is needed for octopuses to properly   
   function," said Aditi Pophale, co-first author of the study and PhD   
   student at OIST.   
      
   The researchers also delved into the brain activity of the octopuses when   
   awake and asleep. During quiet sleep, the scientists saw characteristic   
   brain waves that closely resemble certain waveforms seen during non-REM   
   sleep in mammalian brains called sleep spindles. Although the exact   
   function of these waveforms is unclear even within humans, scientists   
   believe they aid in consolidating memories. Using a cutting-edge   
   microscope built by co-first author Dr. Tomoyuki Mano, the researchers   
   determined that these sleep spindle-like waves occur in regions of the   
   octopuses' brains associated with learning and memory, suggesting that   
   these waves potentially serve a similar function to humans.   
      
   Roughly once an hour, the octopuses entered an active sleep phase for   
   around a minute. During this stage, the octopuses' brain activity very   
   closely resembled their brain activity while awake, just like REM sleep   
   does in humans.   
      
   The research group also captured and analyzed the changing skin patterns   
   of the octopuses when awake and asleep in ultra-high 8K resolution.   
      
   "By filming in such high resolution, we can see how each individual   
   pigmented cell behaves in order to create an overall skin pattern,"   
   said Dr. Meshulam.   
      
   "This could help us create simple skin pattern models to understand   
   the general principles of waking and sleeping patterning behavior."   
   When awake, octopuses control thousands of tiny, pigmented cells in   
   their skin, creating a vast array of different skin patterns. They use   
   these patterns to camouflage themselves in different environments,   
   and in social or threat displays, such as warning off predators and   
   communicating with each other.   
      
   During active sleep, the scientists reported that the octopuses cycled   
   through these same skin patterns.   
      
   The similarities between active sleep and awake states could be explained   
   by a variety of reasons, said the scientists. One theory is that octopuses   
   may be practicing their skin patterns to improve their waking camouflage   
   behavior, or simply maintaining the pigment cells.   
      
   Another intriguing idea is that the octopuses could be re-living and   
   learning from their waking experiences, such as hunting or hiding   
   from a predator, and reactivating the skin pattern associated with   
   each experience. In other words, they could be doing something similar   
   to dreaming.   
      
   "In this sense, while humans can verbally report what kind of dreams   
   they had only once they wake, the octopuses' skin pattern acts as a   
   visual readout of their brain activity during sleep," said Prof. Reiter.   
      
   He added, "We currently don't know which of these explanations, if any,   
   could be correct. We are very interested in investigating further."   
       * RELATED_TOPICS   
             o Plants_&_Animals   
                   # Animal_Learning_and_Intelligence # Behavioral_Science   
                   # Biology # Molecular_Biology # Cell_Biology # Mice #   
                   New_Species # Evolutionary_Biology   
       * RELATED_TERMS   
             o Sleep o Octopus o Dog_skin_disorders o Itch o Skin o   
             Ultraviolet o Sleep_disorder o Leopard   
      
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   Story Source: Materials provided by   
   Okinawa_Institute_of_Science_and_Technology_(OIST)   
   Graduate_University. Note: Content may be edited for style and length.   
      
      
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   Journal Reference:   
      1. Aditi Pophale, Kazumichi Shimizu, Tomoyuki Mano, Teresa L. Iglesias,   
         Kerry Martin, Makoto Hiroi, Keishu Asada, Paulette Garci'a Andaluz,   
         Thi Thu Van Dinh, Leenoy Meshulam, Sam Reiter. Wake-like skin   
         patterning and neural activity during octopus sleep. Nature, 2023;   
         DOI: 10.1038/s41586- 023-06203-4   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/06/230628130356.htm   
      
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