Rat Vision: Humans Combine Visual Systems For Best Sight Of All

Maybe mom wasn't lying when she said she could see everything we were doing as kids? Researchers from the University of Sydney recently discovered new "two-eye" cells that suggest humans have the best vision possible.

Small rodents, such as rats, need to be able to see preying felines from far away and escape their inevitable pounce. That is why rodents have eyes on either side of their head, which they use to scan different fields of view. On the other hand, primates, such as humans, have two forward-facing eyes that capture the same view from slightly different angles and allow us to perform more complex activities such as tennis and threading a needle, according to a news release.

Previously, researchers believed humans and other primates had visual systems in which each eye collected and kept information separate before it reached the brain's visual cortex, where complex processing then combined the two views into a 3D picture -- a process also known as full stereo vision. Additionally, the visual information could be fed directly into deep brain circuits for attention and emotional responses. 

However, recent findings have changed this view and suggest that humans have both full stereo vision and the ability to quickly spot and respond to danger, like rats.

"The brain cells that we identified suggest that humans and other primates retain a visual pathway that traces back to the primitive systems of vertebrates like fish and frogs," Professor Paul Martin, leader of the study from the Sydney Medical School, explained in the release. "These connections may not have been lost during evolution of humans and other primates after all."

Essentially, visual messages from both eyes in primates and rodents enter the brain through a small structure called the lateral geniculate nucleus or LGN, which is made of slivers of nerve cells, the release explained. While LGN cells in rodents may fire in response to messages from either one or both eyes, researchers previously thought LGN cells in primates only responded to inputs from a single eye. However, the recent study revealed a subset of "two-eye" cells squeezed in between the main LGN layers, which reportedly respond to inputs from both eyes and resembles "rat vision."

"At first we thought we'd made a mistake, but we repeated the experiment, and we were right -- the cells responded to inputs from either eye," Natalie Zeater, lead author and Ph.D. student, added.

Further research is required to determine exactly how primates use the two-eye cells to process emotion and fear responses like rats.

"There is no doubt that processing of complex visual information in the cerebral cortex is what enables uniquely human behaviors," Martin concluded. "But these two-eye cells suggest that other types of visual information are just as important -- they allow the human species to survive to engage in the complex behaviors."

Their study was recently published in the journal Current Biology. 

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