The Brain of the Octopus


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If you could have one exotic pet, what would it be and why?

I would have a MASSIVE Great Pacific Octopus. I’ve always wanted a pet that could challenge me in a both wrestling match and in a chess tournament (if you didn’t know, octopuses are highly intelligent creatures - which you will know MUCH more about if you keep reading!)
— Jason Baer

A friendly octopus disguised on a reef. Photo credit: Vlad Tchompalov

A friendly octopus disguised on a reef. Photo credit: Vlad Tchompalov

There is more than one way to build a brain, and the way a brain is built determines how it will experience the world around it. In most animals, this experience is simple and driven by instinct. In some higher order animals, however, the experience of life has evolved into cognition, and the ability to more richly experience life through consciousness. While the degree of consciousness that many vertebrates possess has yet to be understood, our own lively subjective experience suggests that other “higher order” vertebrate animals may share a degree of self-awareness with us.

There is, however, one animal not among the vertebrates that has developed a brain capable of complexity and mysterious intelligence: that animal is the octopus.

The octopus is an invertebrate, and a relative of snails, oysters, and clams. Octopuses and their ‘first cousins,’ squid and cuttlefish, belong more specifically to the cephalopods, which together possess the most complex minds in the invertebrate kingdom. Octopuses can be as small as a fingernail or as large as a Volkswagen, but regardless of their size, seem to possess abilities and intelligence that is light years ahead of their more distant relatives. Just because they are intelligent, though, does not make them similar to us. Evolution built the octopus brain completely differently from how it built our own, and because of that, they experience their world in a wildly different way.

More importantly, the evolution of the octopus brain allows it to do some pretty wild things.

Octopuses are intelligent by any standard; they can solve puzzles, memorize patterns, and use tools to accomplish their goals. They can unscrew jars (even from the inside!) and navigate mazes. When in captivity, they often escape their tanks at night, raiding other ones and feasting on the fish before returning to their own tank by morning. They have been shown to turn off lights by squirting jets of water at the bulbs to short-circuit them, and can tell the difference between (and often have biases toward) their individual human keepers, even if they wear the exact same uniforms. They have short- and long-term memory, and research suggests that they have REM sleep, like us, and may even dream. They can camouflage themselves perfectly to their surroundings in a split second, fully regenerate arms that are cut off, and taste with each of the suckers on their arms.

Octopuses are aware of themselves as individuals, they are aware when they are in captivity, and interacting with them is therefore an experience unlike any other invertebrate: in fact, it’s been likened more to interacting with an alien.

Octopuses in captivity are charismatic, active, and highly intelligent. Photo credit: Janayara Machado

Octopuses in captivity are charismatic, active, and highly intelligent. Photo credit: Janayara Machado

The secrets behind the unique abilities of the octopus, like for every living creature on earth, are written in their genes. To answer some of our questions about these animals, a group of scientists from the University of Chicago led by Cliff Ragsdale sequenced the genome of the California two-spot octopus (Octopus bimaculoides) in August 2015, and their findings were published in Nature. What they discovered surprised the scientific community: these intelligent aliens may not be as different from us as we once thought.

In this article, we will discuss a few of the discoveries found in the octopus genome, and what they can tell us about their remarkable evolutionary path to complexity.

Protocadherins

When we sequence an animal’s genome, we look at all the genes present, which each code for different features of the organism: for example, in humans, one or more genes is responsible for your eye color, your height, and whether or not you’ll have a high risk for cancer. Interestingly, many of the genes that code for development, like the ones that ensure you have two arms and two legs, are actually similar among lots of species: most vertebrates share the same developmental genes, even though they lead to our unique body plans.

Ultimately, two organisms could look completely different from each other, but still share a lot of similarity in their genes, which often code for pretty standard things, like proteins that make up skin, or the camera-like structure of the eye. This is why we share 98.8% of our genes with Chimpanzees; that 1.2% of genetic difference is what allowed us to build civilizations covering the planet, and what keeps chimps still confined to munching bananas in the trees.      

After sequencing the octopus genome, the first thing that the authors did was compare all of the genes found in the genome to known ones in the animal kingdom: some within the mollusks, and some within the vertebrates. What they found first was a large expansion of a particular family of genes called the protocadherins, which code for the development of a complex neural network (ie, a more complex brain). It turns out octopuses contain 168 protocadherin genes, which is 10 times more than any other invertebrate, and more than twice the amount that we possess!

This came as a huge surprise to the scientists, as this expansion of these genes was previously thought to be only present in vertebrates, like us mammals. The presence of these protocadherin genes is likely what allowed the octopus to develop such an intricate brain and an intelligence that makes their snail cousins look like, well, snails.

An octopus solving a puzzle by unscrewing certain jars to receive a food reward.

An octopus solving a puzzle by unscrewing certain jars to receive a food reward.

Interestingly, although we share a family of genes with these eight-armed little weirdos, the way our two brains work is wildly different. Protocadherin genes are responsible for developing neurons and the synaptic connections between them, providing the framework for a nervous system that allows information to be transferred from the body to the brain.

In a human, most of our 100 billion or so neurons are concentrated in our brains, and all of the neurons spread out over the rest of our bodies transmit signals (like pain, heat or sensations of touch) back to our brain, where a decision can be made on how to act. In an octopus, though, most of their 500 million neurons (about the same as a dog) are distributed in small sacs of neurons called ganglia across the eight arms. Only about a third of an octopus’s neurons are concentrated in the brain, forming something called a distributive nervous system.

Picture this: you are standing in front of a steaming, enchanting piece of apple pie. As you stare, the rumble of your stomach reminds you of your hunger, and the smell of cinnamon in the air makes your mouth water. All of these senses assault your brain, which instructs your arm to reach out and take a piece, to bring a bite to your mouth, to chew and swallow and groan in satisfaction. Your brain has dictated each of these actions, has processed every sense, and is the sole reason you ended up eating that piece of pie (or the whole pie, if you’re ambitious).

Human brains use a body map, which allows us to direct specific muscles (such as those in the arm) to accomplish a certain task, and we are limited in our movements by our structure – each of our joints can only move in certain ways.

The octopus uses its eyes as a guide, but its arm functions independently from the brain in searching for food through this maze. Photo credit: Scientific American

The octopus uses its eyes as a guide, but its arm functions independently from the brain in searching for food through this maze. Photo credit: Scientific American

For an octopus, things are different. The centralized brain, which is connected to the eyes, can help the animal perceive the world around it, evading predators and seeking out a juicy crab hiding under a rock. But because an octopus’s neurons are spread into its arms, each arm can think and make basic decisions for itself. The brain does not need to tell the octopus to reach out and grab the crab from under the rock, the arm can come to this conclusion and act on it all on its own.

In this way, the octopus is experiencing the world around it with several different perceiving entities, all linked together through the centralized brain. If you meet an octopus and it extends its arm out to you, you are interacting with only one independent facet of the octopus’s mind; that arm may be the only one of the eight that consciously made the decision to introduce itself.

The octopus brain instead uses a behavior map: because each of its arms can perform different actions almost limitlessly, its brain doesn’t activate specific body parts, it activates a certain behavior (such as ‘capture the crab’) and the arms then carry out the action on their own.

That being said, the octopus brain possesses limitations. The ganglia located in each of the arms possess infinitely fewer neurons than a human brain and is therefore only capable of performing basic actions and processing limited information. Just because each arm can think for itself doesn’t mean each is solving complex equations or possesses different personalities! The brain of an octopus simply operates on a different framework than us, which makes them very good at very different things. This distributive neural network allows the octopus to successfully hunt down prey, escape from predators, and solve simple puzzles. It’s what allows an octopus arm to execute simple tasks even when dismembered, and it’s what has allowed octopuses to survive for over 250 million years.

The eye of the octopus works in the same way as our own, but evolved completely differently. Photo credit: National Geographic

The eye of the octopus works in the same way as our own, but evolved completely differently. Photo credit: National Geographic

The expansion of these protocadherin genes also hints at a much more far-reaching truth: evolution produced this set of genes twice, independently, over the past several hundred million years. We are so distantly related to the octopus that all of these genetic complexities had to arise separately. Features we share with the octopus, such as a camera-like eye (made up of a lens, iris and retina) and large brains, came into being through two entirely different evolutionary pathways, each exposed to entirely different environmental challenges!

What could this say about life outside of our planet? Could organisms shaped by the weird, abstract conditions of other worlds share some of the same features as us, or would they process and manipulate the world around them in new and unfathomable ways? If the former is true, how does that make them any more alien than an octopus?

Zinc-Finger Transcription Factors

Another group of genes found to be expanded in the octopus genome (compared to its molluscan cousins) was the zinc-finger transcription factors, which could be responsible for the octopus’s other strange abilities. A set of genes within this family code for acetylcholine receptors in the suckers covering octopus arms, which allows the creatures to taste with their suckers. Another set of genes seemed to code for proteins called reflectins, which can be found in the octopus’s skin and change the way light reflects off its skin, helping it change color.

The genes within this family are what allows these animals to modify their appearance through changing their texture, pattern, color, and brightness and blend in seamlessly into almost any surroundings. This is what gives them an advantage in hunting and avoiding being hunted.

Can you find the octopus hiding in this photo? Photo credit:

Can you find the octopus hiding in this photo? Photo credit:

The discovery of this set of genes may have unlocked the secret to their incredible camouflaging ability. Videos abound on the internet of octopuses and other cephalopods (like squids and cuttlefish) changing colors and patterns instantaneously; one second they are visible, and the next they are indistinguishable from the reef behind them.

Octopuses have a few different techniques to allow them to do this. The first is a type of cell called a chromatophore: octopuses have these cells just below the surface of their skin, and each contains a sac of brown, orange, red, yellow, or black pigment, like a tiny balloon. When an octopus needs to become inconspicuous, it studies the colors of the background environment, and little muscles attached to the chromatophores stretch certain cells based on what color pigment they contain: if the background is predominantly brown and yellow, like a kelp bed, sacs containing yellow and brown pigments are expanded and the rest of the pigments are shrunk down, and the octopus skin appears yellow and brown.

For more complex colors like blues, greens, silvers and golds, the octopus contains more cells called iridophores and leucophores, which use stacks of plate-like cells to reflect light at different wavelengths, creating beautiful, iridescent colors that allow the octopus to disappear in the blink of an eye.

If changing their color wasn’t enough, octopuses can also change the texture of their skin to match the surrounding environment. Little muscles covering their skin allow them to change the size and shape of bulges on their skin, called papillae, and create bumps and spines; textures that resemble coral, rocks, and marine plants. Some octopuses even use these techniques to mimic other animals (like a venomous stonefish) and thus avoid being eaten!

The discovery of these zinc-finger transcription factors has helped immeasurably in filling the gaps in our knowledge of these complex, weird abilities, and helped us to determine how and when they originated.

The genes of an octopus give it flexibility, camouflage, and the advantage of intelligence on the reef. Photo credit: Mohamed Ahsan

The genes of an octopus give it flexibility, camouflage, and the advantage of intelligence on the reef. Photo credit: Mohamed Ahsan

RNA Editing and Transposons

Finally, the octopus genome illuminated that octopuses are able to engage in a process called RNA editing, in which they can alter the sequences of their RNA, a modified sequence of DNA that allows an organism’s genes to be encoded into proteins. In doing this, octopuses can change the proteins they are producing without altering their base genome, and therefore alter the function of their nervous systems, exhibiting new traits in response to the environment around them.

While they are not the only animal to do this, octopuses utilize RNA editing on an order of magnitude greater than humans and other animals, which may be one of the secrets behind their adaptability and intelligence.  

The octopus genome was also shown to be riddled with transposons, which are movable pieces of DNA that allow genes to move around in the genome. By using transposons, octopuses can quickly (by evolutionary standards) modify the production of certain proteins and therefore change the function of cells and organs in their body. This likely plays a large role in boosting learning and memory, helping octopuses learn quickly to solve puzzles, escape traps, and identify and remember specific individuals, such as their human captors. These strange and unique capabilities have resulted in a creature that is wildly dissimilar from its cousins and from any other form of life on earth.

Having sequenced the full octopus genome, scientists now have a wildly powerful library by which they can better understand the rare, beautiful abilities of the octopus, an organism that, like us, has adapted to survive in a diverse array of environments. There is much more to learn, and scientists are currently trying to use this information to be able to harness some of the octopus’s skills, such as in camouflage, regeneration, and adaptation in order to develop new technologies and to aid in medicine.

Ultimately, the study of the octopus has provided us with a humbling window into the mind of another being, a mind that may live and perceive a world entirely different from our own. Peter Godfrey-Smith, an octopus expert and writer of Other Minds: the Octopus, the Sea, and the Deep Origins of Consciousness writes “the octopus itself is suffused with nervousness; the body is not a separate thing that is controlled by the brain or nervous system. The octopus lives outside the usual brain/body divide.” What more could we learn from an animal so protean, so different from ourselves?

- Jason


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