We know that the eight cunning arms of octopuses can catch fish, fight sharks, open jars, and even camouflage the octopus from potential predators. But these arms are not entirely under the control of the octopus brain. A new study reveals how deep their independence is, even when they are separated from the brain.
The octopus’s nervous system is fascinating. Two-thirds of its neurons reside not in the central brain but in its flexible arms. This, the researchers suspect, lightens the demands on cognitive coordination and allows the octopuses to let their arms do the «thinking» work for themselves.
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And these arms can continue to react to stimuli even when they’re no longer connected to the main brain; in fact, they remain responsive even after the octopus has been euthanized and its arms have been severed.
The study appeared in the September 2013 issue of the Journal of Experimental Marine Biology and Ecology called «Cephalopod Biology.» The researchers examined ten adult common octopuses (Octupus vulgaris). After euthanasia, their arms were separated and kept in cold seawater for about an hour until they were ready for experimentation. When prodded, the suspended arms immediately curled up (after which they slowly returned to their extended position). Tap water and acid evoked similar responses. The horizontal arms also moved away from unwanted stimuli; many of them doubled over and came to the surface. «The results show that the arms are capable of having withdrawal reflexes in the face of ‘noxious’ stimuli without reference to the brain,» the researchers noted.
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These post-mortem reactions could be triggered by nociceptors, neurons that are dedicated to feeling physical danger (the same ones that in our species are responsible for perceiving pain). This is the first evidence that octopuses possess these neurons.
Building on these kinds of experiments on cephalopods, which reveal how intelligent and evolved their system is, the European Union declared last year that cephalopods, like vertebrates, can only be experimented on in ways that minimize pain. , suffering and anguish.
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[ScientificAmerican]
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