Blinded Tadpoles' Hindsights Are 20/20 And Proves You Don't Need A Brain To See

They say hindsight is 20/20, but it could also be illuminating in other ways. Scientists have now successfully transplanted eyes into a tadpole's tail and proven that there doesn't need to be a direct connection to the brain for vision to occur. 

This marks the first time that a vertebrate animal has been able see the world around it despite the brain being left out of the receptive process. 

"One of the big challenges is to understand how the brain and body adapt to large changes in organization," says Douglas J. Blackiston, Ph.D., one of the paper's authors. "Here, our research reveals the brain's remarkable ability, or plasticity, to process visual data coming from misplaced eyes, even when they are located far from the head."

So how exactly were the scientists able to tell if the tadpole can see? After blinding the tadpoles and inserting an eye into their tail, the scientists had to get creative. 

"While physiology can show that an eye sends action potentials [electrical signals] in response to light, a behavioural regime is necessary to show that the brain is receiving such data and processing the information in a meaningful way," Michael Levin, Blackiston's supervisor said. 

The scientists bathed half the tadpoles' environment in blue light and the other half in red light. Venturing into the red light meant these tadpoles got a small zap of electricity to warn them. Most tadpoles showed no preference for either half since they could not tell whether they were in the blue or red zones. Soon, however, six of the tadpoles tested showed a taste for blue light -- just like their full-sighted brethren. 

The findings gave scientists hope that this process could help medical professionals better help human patients with sensory issues, such as blindness. 

"The [tadpole's] ability to see when ectopic eyes are connected to spinal cord and not directly to the brain was stunning," Levin explained. "We believe that future biomedical treatments for sensory or motor disorders may not need to target the original brain locations to restore function,"

The reason only six tadpoles ended up having sight has to do with what where the ectopic eye was extending its nerve endings. If the eye's nerves did not begin innervation, or simply jutted out to a random organ like the gut, eyesight was not achieved. The six tadpoles were part of a small group whose ectopic eyes projected nerve endings towards the spine. 

You can read the full study in the Journal of Experimental Biology.