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in many ways, octopuses are the closest to having aliens on Earth. These intriguing cephalopods are incredibly unique and have three hearts that pump blue blood. Perhaps even more remarkable, however, is the fact that these sea creatures have more than one brain. In addition to a central brain between the eyes, octopuses have separate “mini-brains” at the base of each of their eight tentacles. Unlike most creatures, octopuses have nine brains, and they make use of it incredibly skillfully.
Given all the brainpower they seem to have, they shouldn’t… octopuses rule the world? Not quite. Although they have a central brain and eight separate ganglia or mini-brains, their nervous systems are wired very differently than most vertebrates, including mammals such as humans. Still, compared to most invertebrates, octopuses are remarkably intelligent. For example, these intriguing oceanic creatures have versions of short- and long-term memory. They are even able to recognize individual people by sight.
Nine Brains: The Anatomy of an Octopus’ Nervous System
Octopuses have a central brain. Located between their eyes, this brain has a distinct donut-like shape and forms a ring around the creature’s esophagus. Technically, when an octopus ingests food, it passes through the “center” of this central brain. This is just one of many facts that show how different the nervous system anatomy of an octopus is compared to vertebrates and many other invertebrates.
Neurons are like messengers that send signals and information from the brain to different parts of a creature’s body. All over the body, the typical Octopus – scientific name Octopus vulgaris – possesses about 500 million neurons. That may sound like a lot, but people have more than 100 billion. Octopuses, however, have about the same number of neurons as dogs, known for their ability to learn different commands. Therefore, it is not difficult to say that octopuses are very intelligent, especially for invertebrates.
About 180 million of the 500 million neurons found in an octopus are concentrated in the central brain. About 40 million additional neurons are located in each of the ganglia of each of the eight arms, or tentacles. Therefore, an octopus’s 320 million neurons — more than two-thirds of them — are located at the base of its arms rather than in its central brain. Incredibly, a single octopus arm possesses more neurons than you’ll find in a frog’s entire body — just one of many intriguing facts about their nervous systems.
Because each arm has its own ganglia, or cluster of neurons, each arm can work independently of an octopus’s central brain and other arms. The neurons at the base of each arm are connected with suction cups scattered across them; typically each arm has about 250 suction cups. Each sucker can have about 10,000 neurons, which it uses to detect physical sensations through touch. These neurons also sense chemicals, allowing each arm to smell and taste objects while exploring them.
Octopuses lack proprioception. This means they don’t have a fixed ‘map’ in their head that allows them to know what different parts of their bodies are doing. While a human can focus on a spot on its back without physically seeing it, octopuses completely miss this perception. There’s a good reason for this: unlike humans, octopuses don’t maintain a static body shape. Instead, their bodies are remarkably fluid and are constantly changing to adapt to the environment. Octopuses make up for their lack of proprioception by having those separate “mini-brains” at the base of each of their eight arms.
Benefits of multiple brains
If having multiple brains doesn’t make octopuses the most intelligent creatures on Earth, then what’s the point? As noted above, having several ganglia controlling each tentacle makes up for the creature’s fluid body and lack of proprioception. These mini-brains lighten some of the burden on the central brain, allowing it to perform more complex tasks.
Some of the major benefits of the octopus central brain and eight ganglia makeup include:
- They can respond more quickly to threats because individual ganglia do not need to communicate with the central brain.
- They can fine-tune the movement of each arm and pass the work on to the ganglia.
- They can regenerate new arms if one is cut off – and the new arm even generates a new ganglion.
Octopus Brain and Nervous System vs Vertebrate Brain and Nervous System
Octopus brains have no common anatomy with the brains of invertebrates. Later, we will discuss how evolution played a crucial role in this phenomenon. For now, it’s important to note that while the anatomy is strikingly different, octopuses still share certain cognitive abilities with vertebrates such as humans. For example, they are believed to possess forms of long- and short-term memory and to have some form of sleep. Octopuses are known to playfully explore objects and to recognize and distinguish individual people.
Looking at the relative size of an octopus’ brain to its body, it’s easier to see why they are among the most intelligent invertebrates. The relative size of the brains of octopuses is within the range of that of vertebrates. It’s not as tall as the relative size of mammals’ brains to their bodies, but it’s still significant and sets them apart from the vast majority of invertebrates.
Thanks to the design of an octopus’ nervous system and the relative size of its brain — or brain, as it were — these cephalopods are known for great intelligence in many ways. Examples of things octopuses are smart enough for include:
- Use visual cues to distinguish between two familiar environments and select the best route to a reward
- navigate simple mazes
- unscrewing a jar to get food in – or to escape a jar by unscrewing it to get to the food
- untie knots
- complete simple puzzles
- find their way out of confined spaces
Why are octopuses’ nervous systems so different from humans?
To understand why octopuses are so different from humans — especially why they have nine brains versus one — it helps to consider their evolutionary past. The last common ancestor of vertebrates and mollusks such as octopuses existed more than 600 million years ago, making it more than twice as old as the first dinosaurs.
The evolution of vertebrates and mollusks split off and proceeded independently millennia ago. Vertebrates, including mammals, fish, birds, and reptiles, developed nervous systems of chord-shaped design. This means that there is a nerve cord running down the middle of their back and a brain at one end.
On the other hand, the neurons of invertebrates are usually clustered in several ganglia, which are small nodes arranged around the body and connected to each other. As cephalopods such as octopuses evolved, some of their ganglia became more complex; new ones were often added. Some neurons began to focus at the front of the creature and began to resemble a centralized brain more and more.
Facts about how octopus brains communicate
Although octopuses have nine separate brains, they are still connected and communicating with each other. The eight ganglia, or mini-brains, have their own neural ring that bypasses the central brain. As a result, an octopus’ arms can relay information to each other without the central brain being involved, allowing them to coordinate more effectively.
More research needs to be done, but scientists suspect that an octopus’s nervous system setup gives them localized and top-down control — something important for a creature with a changing body shape and partially decentralized nervous system. The central brain can be used to control an arm’s path through vision, while the individual ganglion at the base of each arm fine-tunes its movement, giving it greater precision. This also allows each arm to taste, smell and feel objects independently.
Embodied Cognition
Researchers suspect that people may use a form of embodied cognition, meaning that their bodies — not their brains — are responsible for some of their “smartness.” In octopuses, embodied cognition is a critical part of how they navigate the world. Their bodies are not separate things controlled by a central brain; instead, they overpowered nervous systems that are aided by various ganglia.
The relationship between the central brain and individual ganglia
In an octopus, the central brain and about 180 million neurons determine what the creature wants or needs; for example, it can send an alert to find food. This command, “find food”, is passed to the ganglia of all eight tentacles. Each tentacle, in turn, collects and processes its own positional and sensory information. From there, each tentacle gives its own commands on how to most effectively move, firm specific areas and relax for optimal efficiency. These ganglia continue to collect and process sensory information as the arms move, sending the data to the central brain, which then makes more elaborate decisions.
Crazy as it may seem, octopuses do indeed have nine brains. These separate brains play an important role in octopuses’ unique intelligence and personalities, making them the most intelligent invertebrates on Earth.
Next one: Saltwater Crocodile Size Comparison: Their Size vs. Humans
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