Eyeball on Tadpole's Tail

Do eyes have to be in the head for them to work? Not according to this strange research by Michael Levin of Tufts Center for Regenerative and Developmental Biology! His team implanted an ectopic eye in the tail of a tadpole and found that it works just fine:

For the experiment, the team surgically grafted “eye primordia” from donor tadpole embryos onto host embryos, 95 percent of which grew eyes on their tails.

The team then used red and blue LEDs to condition the tadpoles to associate red light with a mild electric shock.

Consequently, both tadpoles with normal eyes and those with ectopic eyes developed an aversion to red light and learned to avoid red-lit areas—meaning that the tadpoles with tail “eyes” could see. In contrast, a control group of eyeless tadpoles did not learn to avoid red light.

The spine is known to transmit all kinds of sensory information throughout the body, but the 64,000-eyeball question is how the brain recognizes the signals from the far-flung ectopic eyes for what they are. [...]

“What is really interesting is how the brain knows it is visual data,” said Levin

NatGeo's Weird & Wild Blog has the story: Link


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If the team only tested with colored light, it only proves that the eye can send signals that feels different to the brain (thus allowing the tadpoles to react differently), it doesn't prove that the brain 'knows' what the signal actually is (ie: visual).
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