Octopus arms strike out alone
http://www.nature.com/nsu/010913/010913-1.html
TOM CLARKE
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.
"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.
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.
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
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).
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Useless hypotheses, etc.:
consciousness, phlogiston, philosophy, vitalism, mind, free will, qualia,
analog computing, cultural relativism, GAC, Cyc, Eliza, cryonics, individual
uniqueness, ego, human values
Everything that can happen has already happened, not just once,
but an infinite number of times, and will continue to do so forever.
(Everything that can happen = more than anyone can imagine.)
We won't move into a better future until we debunk religiosity, the most
regressive force now operating in society.
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