Why Two-Thirds of an Octopus’s Neurons Are in Its Arms

About two-thirds of an octopus’s roughly 500 million neurons are in its eight arms, giving those arms unusually independent control.

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An octopus has a remarkably distributed nervous system. It has roughly 500 million neurons overall, and about two-thirds of them are located in the nervous systems of its eight arms rather than in the central brain. Each arm contains substantial neural circuitry that can process sensory information and coordinate movement locally, while still communicating with the central brain. This arrangement helps an octopus control an unusually flexible body with hundreds of suckers and many possible directions of movement. Research also shows that the arm nervous system is organized into repeating segments, adding another layer of local control. This does not mean an octopus has eight completely separate brains, but it does mean its nervous system is far more distributed than the centralized systems familiar in humans. Scientists have studied this unusual design because it offers a different way of thinking about movement, learning, sensation, and animal intelligence. Octopuses are also known for problem-solving and flexible behavior, although researchers caution that intelligence is difficult to compare directly across very different kinds of animals.

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