Octopuses Use Unique Strategies to Coordinate Their Arms when Crawling

Mapping how octopuses control their movement: Dr. Guy Levy (L) and Prof. Benny Hochner at the Hebrew University of Jerusalem's Octopus Research Group. For videos, see below. (Photo: Hebrew University) April 17, 2015: Unlike most animals who are restricted in their movement by an inflexible skeletal system, octopuses have unlimited flexibility. With no rigid skeleton they are able to perform many tasks like crawling, swimming, mating and hunting however, until recently, it was believed that they only have a limited amount of control over their eight limbs.

Dr. Binyamin Hochner and his colleagues show otherwise. Their study, reported in the journal, Current Biology, is the first to systematically attempt to explain how the octopuses coordinate their eight arms. “The orientation of its body and crawling direction are independently controlled, and its crawling lacks any apparent rhythmical patterns in limb coordination,” the scientists explained.

They show that this uncommon maneuverability of octopuses is derived from the radial symmetry of their arms around the body and the simple mechanism by which the arms create the crawling thrust: pushing-by-elongation. “These two together enable a mechanism whereby the central controller chooses in a moment-to-moment fashion which arms to recruit for pushing the body in an instantaneous direction.”

The octopus needs only to choose which arms to activate in order to determine the direction of locomotion. According to the team, the findings lend support to what’s known as the Embodied Organization concept. In the traditional view, motor-control strategies are devised to fit the body. But under this concept, the control and the body evolve together in lockstep within the context of the environment with which those bodies interact.

“This concept, which is borrowed from robotics, argues that the optimal behavior of an autonomous robot or an animal is achieved as a result of the optimization of the reciprocal and dynamical interactions between the brain, body, and the constantly changing environment, thus leading to optimal adaptation of the system, as a whole, to its ecological niche,” said study first author Dr. Guy Levy of the Hebrew University.

“Another important virtue of this type of organization is that every level, including the physical properties and the morphology, contribute to the control of the emerging behavior – and not only the brain, as we tend to think.”

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