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Octopus Arms Found to Have "Minds" of Their Own

John Roach
for National Geographic News
September 7, 2001
 
An octopus may get some mileage out of the excuse "I can't help it, my
arm has a mind of its own," as it goes for an extra sea morsel—at
least more than can a human who reaches too often into the cookie jar.
Neither, however, can lay full blame for their greed on their
appendages.


For humans, the brain inside the human skull, the same brain that sees the cookie and wants to eat it, controls the reach into the cookie jar. Octopus arms, on the other hand, really do have a mind of their own, according to research reported in the September 7 issue of Science.

The brain inside the octopus skull sees a tasty sea morsel and decides to eat it, but to get the morsel into its mouth the brain inside the skull sends a message to a mass of nerves inside the octopus arm. That mass of nerves controls the arm movement to snatch the tasty treat.

"In this hierarchical organization, the brain only has to send a command to the arm to do the action—the entire recipe of how to do it is embedded in the arm itself," said Binyamin Hochner of the Institute of Life Sciences at Hebrew University in Jerusalem, Israel, and co-author of the research.

Controlling Freedom

Octopus arms, unlike human arms, are not limited in their range of motion by elbow, wrist, and shoulder joints. To accomplish goals such as reaching for a meal or swimming, however, an octopus must be able to control its eight appendages.

Trying to work out how octopuses control their flexible arms is the goal of Hochner and his colleagues' research at Hebrew University.

The researchers' observations indicate that octopuses reduce the complexity of controlling their arms by keeping their arm movements to set, stereotypical patterns. For example, the reaching movement always consists of a bend that propagates along the arm toward the tip, said Hochner.

Since octopuses always use the same kind of movement to extend their arms, Hochner and his colleagues wondered if the commands that generate the pattern are stored in the arm itself, not in the central brain. Such a mechanism would further reduce the complexity of controlling a flexible arm.

Severed Brain and Functioning Arm

To find out if octopus arms have minds of their own, the researchers cut off the nerves in an octopus arm from the other nerves in its body, including the brain. They then tickled and stimulated the skin on the arm. The arm behaved in an identical fashion to what it would in a healthy octopus.

The implication is that the brain only has to send a single move command to the arm, and the arm will do the rest.

"This work quantifies in a very nice way what we have suspected based on the large amount of nerves in the octopuses and from the behavior of severed arms during predation," said James Wood of the National Center for Cephalopods at the University of Texas in Galveston.

"Arms have a lot of autonomy and the central brain of an octopus gives high-level commands but may not be aware of the details—in other words, there is a lot of processing of information in the arms that never makes it to the brain," he added.

Robotic Arms

This research shows the mechanism by which octopuses are able to operate an arm that has a nearly infinite range of motion. This has been a long-term goal of the Israeli researchers not only because of their interest in nature, but also to learn how to produce a flexible and robust robotic arm.

"A flexible [robot] arm would not be constricted by the environment. It would be a better robot for unpredicted situations such as a natural disaster or surgery in a delicate area," said Hochner. "It would have infinitely large degrees of freedom which are not constrained by the fixed joints of other robots that are currently used."

Now that the researchers have figured out how octopuses control their flexible arms, the next challenge is to find a material that can replicate the property of an octopus arm. Currently nothing comes close, said Hochner.

In the meantime, scientists will remain awed by the intelligence of octopuses, which are thought to be the most intelligent of the invertebrates (species that have no spine).

"This [research] shows that centralized processing of all incoming information is not the only way to develop a neural network," said Wood. "Interestingly, a significant number of computer science folks take an interest in cephalopods. This gives them one more reason to do so."
 

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