Why Octopuses Don't Tie Themselves in Knots

Octopuses look like a tangle of squishy arms, and yet they never tie their limbs in a knot, finds a new study that determined octopus skin repels itself.

The discovery, published in the latest issue of Current Biology, is helping researchers to design soft robots, such as for surgical use, that can reshape their bodies without becoming a jumbled mess.

It also solves a mystery about octopuses, whose brains appear to be are unaware of what their two legs and six arms are doing. Instead, a chemical produced by octopus skin temporarily prevents octopus suckers from sucking.

"We were surprised that nobody before us had noticed this very robust and easy-to-detect phenomena," co-author Guy Levy of the Hebrew University of Jerusalem, said in a press release. "We were entirely surprised by the brilliant and simple solution of the octopus to this potentially very complicated problem."

We humans don't have such problems because our rigid skeletons limit the number of possibilities as to where our arms and legs could be.

"Our motor control system is based on a rather fixed representation of the motor and sensory systems in the brain in a formant of maps that have body part coordinates," explained co-author Binyamin Hochner.

He continued, "It is hard to envisage similar mechanisms to function in the octopus brain because its very long and flexible arms have an infinite number of degrees of freedom. Therefore, using such maps would have been tremendously difficult for the octopus, and maybe even impossible."

As a demonstration of that freedom, check out this video that shows just how amazingly flexible these marine animals can be:

For the study, Hochner and his colleagues observed the behavior of amputated octopus arms, which remain very active for an hour after separation. (Octopuses can grow their arms back, but doing so is energetically costly.)

Those observations showed that the arms never grabbed octopus skin, though they would grab a skinned octopus arm. The octopus arms didn’t grab Petri dishes covered with octopus skin either, and they attached to dishes covered with octopus skin extract with much less force than they otherwise would.

"The results so far show, and for the first time, that the skin of the octopus prevents octopus arms from attaching to each other or to themselves in a reflexive manner," the researchers wrote. "The drastic reduction in the response to the skin crude extract suggests that a specific chemical signal in the skin mediates the inhibition of sucker grabbing."

Read more at Discovery News