How does an octopus control eight highly flexible and independent arms so well? By David Frank and James Gorman on April 20, 2015.
The octopus is much celebrated for its intelligence and use of camouflage, but one of its most remarkable achievements is how it moves.
The animal somehow controls eight long, flexible arms with a fluidity that can make it look like animated – and very smart – spaghetti. The problem of controlling this kind of movement is, as scientists say, “not trivial.”
Three Israeli researchers set out to record and analyze the movements of an octopus to plumb the secrets of how it coordinates its arms during crawling.
They found that the brain of the octopus doesn’t have to do everything, because the arms, in effect, have a mind of their own.
The researchers – Guy Levy and Binyamin Hochner at The Hebrew University of Jerusalem and Tamar Flash at the Weizmann Institute of Science – published their results April 16 in Current Biology.
An octopus has a kind of mixed body plan. Its head and eyes have a left and right side, so in that sense, the animal is bilateral.
But its arms radiate out from its mouth like the spokes of a bicycle. This radial structure is more like that of a starfish.
The octopus does have a preferred direction of movement, at about 45 degrees to the direction its eyes are facing. Because of how its eyes are built, that angle is optimal for having a good view of its surroundings.
But their analysis showed it can move in any direction without changing its head position. The head and body are controlled independently of the arms movement.
They also showed that when an arm was active in crawling, it always had the same motion. It would shorten and elongate like an inchworm, pushing the whole creature along.
Dr. Levy said that what they concluded, but have not yet proved, is that the central brain of the octopus makes only one decision – which arm to activate. Other parts of the octopus nervous system control the actual movement of the arm.
This fits with the way the octopus nervous system is put together. Its has about 170 million neurons, but its elaborate peripheral nervous system has about 330 million neurons. That system controls the inchwormlike arm movement.
By breaking the process into two parts, Dr. Levy said, “Nature has found a simple solution to a complicated problem.”
He added, “This is an amazing animal.”
