Octopuses sleep and also dream. A study by a group of scientists shows these animals exhibit physiological reactions during sleep that resemble human dreaming.
Like humans, octopuses transition between two sleep stages: a quiet phase and an active phase, comparable to REM sleep in mammals. This raises the question: could octopuses be dreaming?
When octopuses rest, episodes of calm slumber are sometimes interrupted by bursts of rapid activity. Their arms and eyes tremble, breathing quickens, and the skin shifts through vivid colors. These bursts can be seen in video evidence.
Researchers at the Okinawa Institute of Science and Technology and collaborators at the University of Washington examined brain activity and skin patterns in octopuses. They found the neural activity and skin responses during active sleep closely resembled those seen when the animal is awake.
This wake-like activity also occurs in mammals during REM sleep, the phase where most dreams take place.
activity winds during deep sleep
When at rest, an octopus appears completely immobile, yet about once every hour it shows periods of wake-like activity during sleep. These moments reveal patterns similar to those observed when the animal is awake.
The study, published in Nature on June 28, highlights the similarities between octopus and human sleep behavior and offers insights into the origin and function of sleep.
Octopuses show similarities to mammals during sleep, suggesting parallel mechanisms in brain activity and behavior during rest.
Lead author Professor Sam Reiter of OIST notes that two-stage sleep evolved independently in creatures with large brain structures but very different brains from vertebrates, indicating a shared feature of complex cognition involving an active sleep-like wakefulness stage.
Leenoy Meshulam of the University of Washington adds that the two-stage sleep pattern may reflect a broad principle of brain function underlying cognition across species.
To test sleep, scientists exposed octopuses to physical stimuli and found that responses were stronger during both calm and active sleep than during wakefulness. They also observed that interrupting active sleep prompted earlier and more frequent return to the active phase.
Aditi Pophale, a co-author and doctoral student at OIST, emphasizes that this compensatory behavior indicates the active phase is essential for proper functioning.
Perceived sleep waves
The team studied brain activity in both wakeful and resting states, noting brain waves during calm sleep resemble non-REM sleep spindle patterns seen in mammals.
Although the exact role of these waves remains uncertain, scientists speculate they help with memory consolidation. With advanced microscopy, researchers located these waves in brain regions linked to learning and memory, suggesting a possible shared function with humans.
Approximately one minute of active sleep occurs roughly every hour, during which brain activity mirrors the awake state, similar to human REM sleep.
examine the skin
The group captured and analyzed skin color changes in octopuses during wakefulness and sleep using ultra-high resolution imaging.
Observing at high resolution reveals how pigment cells coordinate to create overall skin patterns. This helps in modeling simple skin pattern dynamics to understand sleep and wake behavior in octopuses.
When awake, octopuses control thousands of pigment cells to camouflage, signal, and communicate. During active sleep, they display similar skin patterns, suggesting a link between daytime experiences and sleep patterns.
Octopuses may remember waking life by changing their skin pigment.
The researchers propose several explanations for these similarities. One idea is that skin patterns are studied to improve camouflage or preserve pigment cells.
Remember what you did while awake while you were sleeping
Another possibility is that octopuses remember and learn from daytime experiences, such as hunting or avoiding predators, and reactivate corresponding skin patterns during sleep. In other words, they may be dreaming in a visual form.
Reiter explains that while humans can report dreams verbally, octopus skin patterns visually indicate brain activity during sleep.
The researchers acknowledge that more work is needed to determine which explanation is correct, and they remain keen on further study.
Reference work: Nature article 2023: s41586-023-06203-4 (Nature).
…
This inquiry reflects the broader fascination with sleep across species and the quest to understand its origins and functions. It is part of a larger effort to map how cognition and sensory processing persist through rest.