Published online 7 September 2001 | Nature | doi:10.1038/news010913-1


Octopus arms strike out alone

Robot research could learn from octopus limbs.

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You'd have thought that of all creatures, the octopus would keep track of what its arms are up to. But an octopus' arms, it turns out, often function completely independently of its brain.

The finding solves the biological conundrum of how the octopus coordinates and controls its eight super-supple arms. Understanding this could help engineers design better robots.

By electrically stimulating nerves in amputated octopus arms, or just by tickling the skin near them, Binyamin Hochner, of the Hebrew University of Jerusalem, and colleagues made the limbs reach outwards just as an intact octopus reaches for a piece of food.

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"We saw autonomous control of the entire arm," says Hochner. This and other simple experiments demonstrate that the nervous control program for reaching is written into the arm's nerves, the team believe.

Joints constrain other animals' limbs, making the mental processing of coordinated movement easier to understand.

But octopus arms can adopt a virtually infinite number of positions. Each tentacle contains 50 million nerves, of which around 40,000 are connected to muscles. As only a few nerves run from each tentacle to the animal's brain, however, biologists have puzzled over how the movement of one such arm - let alone eight - is coordinated.

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Hochner's group suggests that by abdicating control of often-repeated tasks such as reaching, the octopus brain is free to concentrate on other things. "This control strategy overcomes the complexity of [the arm's] structure," says Hochner.

This idea is borne out by octopus behaviour: the animals execute most tasks using just a small repertoire of arm movements. The team now plans to try to stimulate and then model these stereotypical moves.

Bring on the Octobots?

Robotics experts long to understand octopus arm control. It may provide clues for building automatons that, unlimited by joints, can move in every dimension simultaneously.

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Until now, the animals' sophistication had been baffling. "They were just too complex to go after," says Bob Full, who builds biologically inspired robots at the University of California, Berkeley. Researchers couldn't understand how to program a computer to control limbs with unlimited freedom of movement.

Now they might not have to. "A robot could have no brain at all, yet still be highly manoeuvrable," says Full. Hochner's work could be "the first step towards building the next great manipulator," Full hopes. 

  • References

    1. Sumbre, G., Gutfreund, Y., Fiorito, G., Flash, T. & Hochner, B. Control of Octopus Arm Extension by a Peripheral Motor Program. Science 293, 1845 - 1848 (2001). | Article | PubMed | ISI | ChemPort |