Two-thirds of an octopus's neurons are located in its arms rather than its brain.

The common octopus (Octopus vulgaris) possesses approximately 500 million neurons in total, but only about one-third of these are located in the central brain. The remaining two-thirds are distributed throughout the eight arms in a series of clusters called ganglia. This unique anatomical structure creates a decentralized nervous system where the arms function with a high degree of autonomy.Research led by Dr. Guy Levy and Professor Binyamin Hochner at the Hebrew University of Jerusalem has shown that this arrangement allows the central brain to simply trigger a movement while the arm's local nervous system handles the complex coordinates. Each arm is equipped with hundreds of suckers that contain specialized sensory receptors for both touch and taste. This allows the limbs to process vast amounts of sensory data locally without overwhelming the central brain.In a famous 2001 study published in Science, researchers demonstrated that severed octopus arms would still reach out and grasp food when stimulated. This occurs because the peripheral nervous system contains the necessary motor programs to execute complex tasks independently. This evolutionary adaptation is crucial for a predator that must manage eight highly flexible limbs simultaneously while navigating complex reef environments.The decentralization also provides a survival advantage during limb loss. Because the arm's 'intelligence' is localized, the octopus can lose a limb to a predator without losing its primary cognitive functions. This remarkable neural architecture continues to inspire the field of soft robotics, where engineers aim to create machines that can perform complex movements without a central processor.