A sleeping octopus can look almost ghostly. Its body lies still, its eyes close and its skin may fade toward a pale, uniform color. Then, without waking, the animal seems to erupt into activity. Its eyes move. Its arms twitch. Its breathing changes. Dark patches race across the skin, followed by mottled camouflage, pale flashes and abrupt changes in texture.
Videos of this behavior have inspired an irresistible interpretation: the octopus must be dreaming. Perhaps it is replaying a hunt, hiding from an imaginary predator or changing camouflage to match scenery that exists only inside its sleeping brain.
That possibility is scientifically intriguing, but it is not yet a demonstrated fact. What researchers have established is arguably just as remarkable: octopuses alternate between at least two distinct sleep stages, including a short “active sleep” state whose neural activity and behavior resemble important features of rapid-eye-movement sleep in vertebrates. During those active episodes, the octopus's skin can become an unusually visible window into what its nervous system is doing.
An animal whose brain is connected to its skin
Octopuses do not change color in the way human skin gradually tans or blushes. Their transformations can happen in fractions of a second because the nervous system directly controls specialized structures in the skin.
Thousands of pigment-containing organs called chromatophores can expand and contract, exposing or concealing colors. Other skin structures contribute reflective and iridescent effects, while muscles can raise bumps called papillae and alter the apparent texture of the body. Together these systems allow an octopus to transform its appearance with extraordinary speed.
When awake, it uses this ability for camouflage, threat displays, communication and behavior associated with hunting. A rock-like pattern can dissolve into a different arrangement as the animal crosses the seabed. Because the patterns are neurally controlled, watching the skin gives scientists something unusual: a visible output of activity occurring inside the octopus nervous system.
That is what makes the sleeping color changes so provocative. The animal is not simply losing pigment control as it relaxes. During certain sleep episodes, it rapidly cycles through structured patterns that strongly resemble patterns it produces while awake.
Quiet sleep, then a minute of extraordinary activity
Researchers had previously observed two sleep-like states in octopuses, but a major 2023 study in Nature examined the phenomenon in much greater neurological detail. Scientists at the Okinawa Institute of Science and Technology and collaborators studied the nocturnal species Octopus laqueus, recording behavior, skin patterning and electrical activity in the brain.
During what the researchers call quiet sleep, the animals generally remained still with closed eyes, a flattened posture and pale skin. Roughly once an hour, however, this state was interrupted by an active bout lasting about a minute. The octopuses moved their eyes and bodies, their breathing became faster and more irregular, and their skin flashed through rapid changes of color and pattern.
Could the animals simply have been briefly waking up? The researchers tested that possibility. Octopuses in both quiet and active states required stronger stimulation to respond than awake animals did, indicating a raised arousal threshold — a classic characteristic of sleep. When researchers disrupted the active stage, the animals subsequently entered it sooner and more frequently. That rebound effect suggested the state was homeostatically regulated: the octopus's nervous system appeared to need it.
This fits into the broader puzzle of why animals sleep at all. Even familiar behaviors around sleep and waking, such as those explored in IMOOND's look at why we yawn and why yawning can spread between individuals, reveal how much remains unresolved about the regulation of brain states. Octopuses make the mystery more profound because their lineage diverged from ours more than half a billion years ago.
The octopus version of REM sleep?
The most striking result came from recordings of the brain. During active sleep, electrical activity became remarkably similar to activity recorded while the octopus was awake. Mammalian REM sleep also has this paradoxical quality: a sleeping brain can enter a state that, in important respects, looks surprisingly wake-like.
The behavioral similarities add to the comparison. Active octopuses show eye movements and body twitches, while their skin becomes dynamically active. In humans and other mammals, REM sleep is associated with rapid eye movements, vivid dreaming and distinctive patterns of neural activity.
But scientists deliberately use language such as “REM-like” rather than declaring that octopuses have human-style REM sleep. Vertebrate and cephalopod nervous systems have profoundly different anatomy and evolutionary histories. The similarities may represent convergent evolution — two distant branches of animal life independently arriving at alternating quiet and active sleep states because such organization provides some benefit to a complex brain.
Quiet sleep is equally interesting. The 2023 researchers found 12–18-hertz oscillations in brain regions associated with learning and memory. These events resembled mammalian sleep spindles in their frequency and duration. Sleep spindles in mammals are associated with non-REM sleep and have been investigated for roles in memory processing, although the apparent similarity does not prove identical function in octopuses.
Taken together, the results make the simple idea of an invertebrate brain merely “switching off” during sleep increasingly difficult to maintain.
So are those changing colors actually dreams?
This is where the evidence ends and the fascinating speculation begins.
Humans can wake up and describe a dream. An octopus cannot tell a researcher whether the dark pattern that swept across its mantle corresponded to an imagined crab, a remembered coral reef or nothing resembling a subjective scene at all. There is currently no direct test that can establish dream experience in an octopus.
Nevertheless, the skin patterns provide clues worth investigating. Using high-resolution video and computational analysis, the 2023 team found that active-sleep patterns occupied much of the same pattern space as those produced during waking. The sleeping animals were not generating an entirely unrelated set of random colors.
One hypothesis is therefore that the brain is replaying aspects of waking experience. If an octopus reactivates neural patterns associated with hunting, camouflage or a threatening encounter, the motor commands connected to those experiences might partially leak onto the skin. Under that interpretation, the spectacular color display could be an external trace of something analogous to memory replay — and perhaps, though not necessarily, dreaming.
Another explanation is more mechanical. Octopuses may use active sleep to refine or maintain the complex neural programs that control their skin. Producing effective camouflage requires coordinating huge numbers of chromatophores and other skin structures. The sleeping brain could be rehearsing that system without recreating any remembered experience.
The researchers themselves emphasize that neither explanation has been established. The patterns could reflect memory processing, motor refinement, another unknown sleep function or some combination of processes.
A dream would be especially strange in an octopus
If future experiments provide stronger evidence that octopuses dream, the discovery would have unusual evolutionary significance. Mammals and octopuses did not inherit complex brains from a recent common ancestor. Their sophisticated nervous systems evolved along radically different routes.
An octopus has a large central brain, but an enormous proportion of its neurons are distributed through its arms. Its body is soft and extraordinarily flexible. Its visual system, motor control and camouflage have no close equivalent in human biology. Whatever an octopus experiences while awake is already constructed by a nervous system very different from ours.
Its hypothetical dreams therefore need not resemble cinematic human dreams. Even asking whether an octopus “sees” an imaginary scene while asleep may impose human assumptions on an animal whose perception and body representation are fundamentally different.
This is why the color-changing videos are scientifically valuable beyond their viral appeal. The skin offers researchers a rare behavioral readout of neural control. If scientists can learn which waking situations correspond to particular patterns, and then compare those patterns with sequences produced during sleep, they may eventually test whether sleeping brains replay meaningful fragments of recent experience.
For now, the strongest conclusion is both cautious and extraordinary. Octopuses really do sleep in alternating stages. Their active sleep includes wake-like brain activity, twitching eyes and bodies, altered breathing and rapid skin patterns borrowed from their waking repertoire. It resembles REM sleep in several important ways, despite evolving in a lineage separated from vertebrates by roughly 550 million years.
Do they dream? Science cannot yet say yes. But every time a sleeping octopus turns pale, darkens suddenly and sends another camouflage pattern flowing across its skin, it gives researchers something most sleeping animals keep hidden: a visible hint that its brain is far from quiet.
