Scientists Think An Octopus Might See Light Through Its Arms

Whilst octopuses are an already fascinating species to many with their odd-shaped bodies and long tentacles, scientists have been examining a potentially new and interesting theory surrounding their many arms.

What we already know

Scientists already know that octopus’ arms react to light as their skin can change color when it’s exposed. This is because they have pigment-filled sacs called Chromatophores which help them blend effortlessly into their surroundings.

Stumbling upon an unusual response

While trying to encourage a Chromatophore response by shining a light onto an octopus’ arms, Tal Shomrat and Nir Nesher of the Ruppin Academic Center in Israel, unfortunately, had little luck. Instead, the response they were getting was that the octopus was pulling its legs away from the light, which was something that they hadn’t expected to encounter. Due to this, the researchers decided to amend their study, and instead take a look at why the octopus was reacting in this way.

Putting the theory to the test

To test why the octopus was reacting in this way, Shomrat and Nesher decided to place the octopus in a tank covered in an opaque black tarp before training the octopus to feel for food through a hole in the top of the tank. While the octopus was feeling for the pieces of fish outside the hole, they would shine a light randomly onto the arm to see what happened. The result?They recorded that 84% of the time they shone the light onto the arm, the octopus would pull the arm away from the light, even though it couldn’t see the light with its eyes.

Reflex or brain?

Shomrat and Nesher next performed some experiments to try and identify the route of the response. To begin with, they shone the light at various parts of the octopus’s arm and found that the part of the arm that appeared to react most sensitively was the tip. They then performed the same test on several anesthetized octopuses. If this was a reflex, it should have also been visible in a sleeping octopus. The experiment found that although the Chromatophores in the arm did react to the light, it wasn’t the same reaction they had seen already. In another experiment, they shone a light onto the food outside of the tank where they noted that the octopus would pull away from the food when it was touched by the light, but they noticed it would eventually override the instinct and grab the food anyway.

The findings

Once they had completed their experiments, Shomrat and Nesher concluded that the response was one of the brain rather than nerves – and the octopuses were, in a way, seeing with their arms. The pair feel this is a response that may have evolved to protect the Octopus’s arms from predators mistaking them for food.

While there is still more work to be done when it comes to investigating if an octopus can see through its arms, there is still plenty of work to understand what makes these creatures even more incredible.

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