Not just a window to the soul, the eye has a few tricks of its own. Newly discovered eye cells can warn us that an object is coming nearer, and do so without the brain's help. This ability may have evolved to speed escape from predators.
Neurons that fire in response to horizontal and vertical movements had already been found in the retinas of mammals, but the only cells known to be sensitive to approaching objects were in the brain.
While investigating mouse eye cells, Botond Roska at the Friedrich Miescher Institute for Biomedical Research in Basel, Switzerland, and colleagues noticed that one type behaved unusually in response to movement. Further analysis of this one kind of retinal cell revealed that it fired only when an object approached.
The researchers suspect that people have similar cells, which alert us to approaching objects faster than our brain cells can. "It's an alarm system that's as close to the front end of the organism as possible," says Roska. "If you left it to the brain to respond, it might be too late."
Next, Roska plans to discover how the approach-sensitive cells evoke a reaction in the brain.
"This is exciting work," says Russell Foster, a neuroscientist at the University of Oxford. "How the nerve cells of the visual system work out that an object is approaching represents a very old question in neuroscience."
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