Thursday, November 20, 2025

The Octopus has 9 brains

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The statement that an octopus has nine brains is a common way to describe its decentralized nervous system
. In reality, an octopus has only one central brain, but it also has eight smaller clusters of nerve cells, called ganglia, at the base of each of its arms that function as "mini-brains". These allow each arm to move and react with a high degree of independence. 
This video explains why the octopus's decentralized nervous system allows its arms to act independently:
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The central brain and arm ganglia 
  • Central brain: The single, donut-shaped brain located in the octopus's head controls overall functions, like overall decision-making, and contains about 180 million neurons.
  • Arm ganglia: Each of the eight arms has a cluster of neurons that can process information and control the arm's movements independently without needing constant input from the central brain. This allows an arm to, for example, open a jar while the rest of the body is focused on something else. 

How the system works
  • The central brain sends high-level commands, such as "search for food".
  • The ganglia in each arm receive these commands and then gather their own sensory information to decide how to best execute the command.
  • This decentralized system is highly efficient, as it allows the octopus to manage a complex body and process a lot of sensory input, especially since its arms can taste and touch independently.
  • As the arms process information, they send relevant data back to the central brain to help with larger decisions. 

To learn more about the octopus's decentralized nervous system, you can read this article from A-Z Animals and this one from Eryn Lynum. You can also watch this AumSum video for a simplified explanation. 
  • How Many Brains Does an Octopus Have? - Eryn Lynum
    Feb 18, 2025 — One Central Brain – This is the octopus's main brain, controlling its overall functions. And here's something wild—it'
    Eryn Lynum
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Dive deeper in AI Mode
  • Nine Brains Are Better Than One: An Octopus' Nervous System
    Apr 7, 2021 — An experiment shows that an electrically stimulated octopus arm (right), when detached from its central nervous system ...
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  • Does an Octopus have Nine Brains? + more videos - YouTube
    Nov 5, 2024 — Does an Octopus have Nine Brains? + more videos | #aumsum #kids #cartoon #science - YouTube. ... This content isn't ava...
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