Octopus Dreaming: Color Patterns

The idea that animals dream has long fascinated pet owners and biologists alike. While we often see dogs running in their sleep, recent observations in marine biology have shifted the focus to the ocean floor. Scientists have recorded sleeping octopuses displaying rapid, kaleidoscopic color shifts. These changes suggest that these intelligent cephalopods experience complex dream states similar to human REM cycles.

The Discovery of "Active Sleep" in Cephalopods

For years, researchers assumed invertebrates had very simple sleep cycles. However, recent studies from the Okinawa Institute of Science and Technology (OIST) and the Federal University of Rio Grande do Norte in Brazil have proven otherwise. By observing the species Octopus insularis, scientists identified two distinct sleep stages:

• Quiet Sleep: The octopus remains still. Its skin is pale and the pupils are contracted to narrow slits. This stage makes up the majority of their rest.
• Active Sleep: This stage occurs briefly, usually lasting less than a minute. During this phase, the octopus changes color, twitches its tentacles, and moves its eyes rapidly.

These findings were published in the journal iScience by lead author Sylvia Medeiros. The team observed that during active sleep, the octopuses cycled through skin patterns identical to those used when they are awake and interacting with their environment. This indicates that the brain activity during this state is remarkably similar to the activity seen when the animal is awake.

How the Color Shifts Work

To understand how an octopus might project a dream onto its skin, you have to understand its biology. Octopuses are masters of camouflage. They achieve this through specialized cells called chromatophores.

Chromatophores are pigment-filled sacs in the skin. Muscles attached to these sacs expand or contract to display different colors. An octopus controls these muscles with its nervous system. This direct link between the brain and the skin is what makes the “dreaming” theory so compelling. If the brain stimulates these nerves during sleep, the skin acts as a screen displaying the neural activity.

During the observed active sleep cycles, the octopuses displayed specific patterns:

• Camouflage: Mottled patterns used to hide from predators in sand or coral.
• Aggression: Darker colors often associated with threat displays.
• Attention: Distinct banding patterns used when the animal is focused or hunting.

Because these changes happen without any external stimulus, researchers believe the trigger is internal. The brain is replaying scenarios, and the body is reacting physically.

The Famous Case of Heidi the Octopus

While peer-reviewed studies provide the data, a documentary brought the concept to the public. In a clip from the PBS series Nature, a marine biologist named David Scheel narrated the sleep of an octopus named Heidi.

As Heidi slept hanging upside down in her tank, her color shifted dramatically. Scheel speculated on the narrative of her dream based on the sequence of colors:

1. Pale white: She began in a deep, quiet sleep.
2. Yellow and bright: She transitioned to a color often seen when an octopus leaves the sea floor.
3. Deep red/dark: This color usually appears when an octopus strikes at prey.
4. Camouflage: Finally, she adopted a textured, mottled pattern similar to sea kelp, which an octopus does to hide after a successful hunt.

While we cannot interview Heidi to confirm the plot of her dream, the sequence aligns perfectly with the behaviors she exhibits while awake. This anecdotal evidence supports the more rigorous data collected by Medeiros and her team.

Convergent Evolution: Why It Matters

The existence of active sleep in octopuses is a major discovery for evolutionary biologists. Humans and octopuses are separated by over 500 million years of evolution. Our last common ancestor was likely a simple, worm-like creature with a primitive nervous system.

Despite this massive evolutionary gap, both species evolved complex brains and similar sleep structures independently. This is known as convergent evolution. It suggests that complex sleep stages like REM (Rapid Eye Movement) are not just a quirk of mammals. Instead, they might be a fundamental requirement for any complex nervous system.

If a brain is large enough to learn and solve problems, it may need active sleep to process information. For the octopus, this processing results in a visible light show.

What Are They Actually Dreaming About?

If we accept that these color shifts represent dreams, the content likely revolves around survival. The brain activity during active sleep is thought to be necessary for memory consolidation.

Just as a human might dream about a stressful day at work or a math test, the octopus is likely solidifying memories related to:

• Spatial mapping: Remembering the layout of the reef.
• Hunting tactics: Replaying the movements required to catch a crab or shrimp.
• Predator avoidance: Reinforcing the camouflage patterns that worked successfully during the day.

The “active sleep” phase in Octopus insularis typically occurs after long bouts of quiet sleep, roughly every 30 to 40 minutes. This cyclical nature mirrors the sleep cycles found in birds and reptiles, further cementing the octopus’s status as an honorary vertebrate in terms of intelligence.

Frequently Asked Questions

Do all octopuses change color when they sleep? Most research focuses on specific species like Octopus insularis and Octopus vulgaris. While it is highly likely that other shallow-water octopuses with camouflage abilities experience this, deep-sea octopuses that rely less on vision may have different sleep patterns.

Is the octopus actually seeing images in its sleep? It is impossible to know for sure. However, the rapid eye movements associated with active sleep suggest visual processing. In humans, this stage correlates with vivid visual dreaming.

How long does the dreaming stage last? It is very short. In the studies conducted by the OIST, the active sleep phase typically lasted less than one minute. This is much shorter than human REM cycles, which can last up to an hour.

Can octopuses have nightmares? If they dream about daily life, they likely replay negative experiences too. There is anecdotal evidence of octopuses waking up abruptly and releasing ink (a defense mechanism), suggesting they may have been reacting to a perceived threat in a dream.

Why don’t they wake up while changing colors? Like humans, octopuses appear to have a mechanism that prevents them from fully acting out their dreams physically, even though their skin reacts. This “paralysis” keeps them from swimming into danger while their brain is occupied.