An octopus has one brain. It is located in its head. However, unlike other creatures, not all of its neurons are located in its brain.
What? Look at it this way, imagine that the “stuff” that provides you with your brain processing power, instead of being solely in your head, were to be distributed throughout your arms and legs. That is the case with the octopus.
An octopus has approximately 500 million neurons. Of those, 30 to 40 percent reside in its formal brain located in its head. The remaining neurons are distributed throughout the animal’s eight arms.
The schematic structure for this distribution of neurons throughout the octopus is what gives rise to popular, although erroneous, myths that an octopus has multiple brains. You may read comments about an octopus having nine or ten brains. While they do not have multiple brains, the truth about the neural network of an octopus is still quite amazing.
The neurons that are in the arms link up to a denser cluster of neurons that is located at the base of each arm. These clusters are known as “ganglia”. Having eight arms, this means that an octopus has eight ganglia.
Each ganglia is connected to the formal brain of the octopus and are subordinate to it but also operate in an autonomous fashion. Each ganglia can receive sensory input from the arms and process it in a remote way without having to route it first to the main brain.
Think of each ganglia as a remote command post with the brain being the main headquarters. Each remote command center can process information on its own. However, when needed, input from the remote command centers (ganglia) can be unified in the main headquarters (the brain). Also, when precise coordination in arm movements is required, the ganglia can communicate and coordinate with each other without having to go through the main brain.
The way that the neurons are distributed throughout the arm from the ganglia not only allows each arm to process sensory input individually but also amplifies what they sense. The arms of the octopus are not only sensitive to touch and temperature but they can also detect changes in light, color and taste. Yes, when you hear claims that an octopus can taste with its arms, it’s true.
An additional benefit to the ganglia is that the main brain of the octopus can focus on problem solving, perhaps even planning. It also allows for a large number of neurons in the main brain to be dedicated to processing input from the optic nerve of the octopus. This allows them to take advantage of their highly developed and advanced eye structure.
Imagine if you were able to taste food simply by touching it, or “seeing” something just by rubbing your arm or leg against an item without looking at it with your eyes. Imagine if your brain did not have to handle menial tasks such as processing raw sensory data or keeping you coordinated. Imagine freeing up your brain for more profound thought and analysis. That is how the octopus brain system works. You have to admit, that it is amazing.
