"Even Octopuses Can Dream"… Japanese Scientist Announces REM Sleep Observation

Observation of 29 Rakeus Octopuses... 'Nature' Publication
Two-Stage Forms of 'Quiet Sleep' and 'Active Sleep'

A study has revealed that octopuses enter a 'REM sleep' state, previously thought to be exclusive to vertebrates, and it is presumed that they also dream during this state, drawing significant attention.

On the 28th (local time), according to the British daily The Guardian and others, a research team from the Okinawa Institute of Science and Technology Graduate University (OIST) and other institutions observed 29 nocturnal octopuses of the species Octopus laqueus during the day and confirmed that octopuses do indeed sleep.

When the researchers tapped the tank and observed the octopuses' responses, the octopuses exhibited different reactions depending on whether they were awake, in a quiet sleep phase, or in an active sleep phase. Specifically, octopuses required stronger stimuli to respond when they were asleep compared to when they were awake.

The photo is not related to the specific content of the article [Image source=Pixabay]

The researchers also discovered that octopuses exhibit two types of sleep: 'quiet sleep' and 'active sleep.' It was observed that sleeping octopuses suddenly changed their skin color, moved their eyes and arms, and breathed rapidly during the active sleep phase, then returned to a quiet sleep state. This behavior lasted about one minute and repeated at roughly one-hour intervals, resembling the behavior seen in vertebrates, including humans, during REM sleep.

REM (Rapid Eye Movement) sleep refers to a sleep stage characterized by rapid eye movements. Although the individual is clearly asleep, brainwave patterns resemble those of the awake state, which is why REM sleep is also called paradoxical sleep. Humans typically experience 5 to 7 REM sleep cycles at 90-minute intervals throughout the night, during which they dream and sometimes move parts of their body. Until now, REM sleep was believed to be experienced only by vertebrates.

Furthermore, the researchers confirmed that when octopuses were tickled with a brush to prevent them from sleeping for two days, the proportion of active sleep increased and they entered the active sleep phase more quickly. Analysis of the octopuses' brain activity also revealed neural activity similar to the 'sleep spindle' brainwaves observed in humans during non-REM sleep when the octopuses entered the quiet sleep state. Sleep spindles play a key role in consolidating information acquired during the day into long-term memory in humans.

Sam Reiter, the lead author of the study, stated, "We can associate specific skin patterns seen when the octopus is awake with situations such as hunting, social activity, threat display, and camouflage, and we have demonstrated that these patterns reappear during the active sleep state." However, the research team took a cautious stance on equating the octopuses' skin color changes during active sleep with dreaming, as these changes might serve to enhance camouflage abilities or maintain pigment cells during sleep.

Professor Reiter added, "At present, we do not know which of these hypotheses is correct. More research is needed in the future." The results of this study were published in the scientific journal Nature.

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