an octopus's favorite arm -- 4/25/16

Today's selection -- from The Soul of an Octopus by Sy Montgomery. Octopuses are intelligent and aware, but how much of that is centrally located in their "brain?" Is it possible that they have a "distributed mind" with each arm having a mind of its own?

"Each arm seemed like a separate creature, with a mind of its own. In fact, this is almost literally true. Three fifths of octopuses' neurons are not in the brain but in the arms. If an arm is severed from an octopus's body, the arm will often carry on as if nothing has happened for several hours. ...

"It's even possible that octopuses have some shy arms and some bold arms. University of Vienna researcher Ruth Byrne reported that her captive octopuses always choose a favorite arm to explore new objects or mazes -- even though all their limbs are equally dex­terous. She looked at eight octopuses, all of whom would jump on prey with all their arms, curling both the interbrachial web and arms around whatever food item they would find. But they all used combinations of one, two, or three favorite arms when manipulat­ing objects. Her team counted the octopuses using only forty-nine different combinations of one, two, or three arms for manipulating objects, when, according to her calculations, 448 combinations were actually possible if all eight arms were involved.

"This could simply be an instance of handedness. Tank-bound octopuses, at least, are known to have a dominant eye, and Byrne thinks this dominance might be transferred to the front limb nearest the favored eye.

"But the bold versus shy arms could be something quite different. While arms can be employed for specialized tasks -- for example, as your left hand holds the nail while your right hand wields the ham­mer -- each arm may have its own personality, almost like a separate creature. Researchers have repeatedly observed that when an octo­pus is in an unfamiliar tank with food in the middle, some of its arms may walk toward the food -- while some of its other arms seem to cower in a corner, seeking safety.

"Each octopus arm enjoys a great deal of autonomy. In experi­ments, a researcher cut the nerves connecting an octopus's arm to the brain, and then stimulated the skin on the arm. The arm behaved perfectly normally -- even reaching out and grabbing food. The ex­periment demonstrated, as one colleague told National Geographic News, 'there is a lot of processing of information in the arms that never makes it to the brain.' As science writer Katherine Harmon Courage put it, the octopus may be able to 'outsource much of the intelligence analysis [from the outside world] to individual body parts.' Further, it seems 'that the arms can get in touch with one an­other without having to go through the central brain.'

" 'Octopus arms really are like separate creatures,' Scott [Dowd, aquarium biologist at the New England Aquarium] agrees. Not only can they grow new arms when needed; there is evidence that, on occasion, an octopus chooses to detach its own arm, even in the absence of a predator. (Tarantulas do this too -- if a leg is injured, they will break it off and eat it.)



Sy Montgomery


The Soul of an Octopus: A Surprising Exploration into the Wonder of Consciousness


Simon & Schuster Ltd


Copyright 2015 by Sy Montgomery


14, 160-161
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