In a lab shrouded in darkness, scientists looking at mouse retinas discovered something eye-popping.
Animals in darkness need to adjust their eyes to navigate a host of situations, whether they’re straining to see the galaxy next door or avoiding being turned into dinner. In most cases, the light-sensing machinery in eyes changes to take in more of the meager photons available when lighting is dim.
But a new study shows that mice, at least, have a different trick up their furry sleeves: a type of night vision keyed to motion. Described this week in the journal Neuron, the research suggests that one type of eye cell allows mice to be a bit more sensitive to movement in general when it’s dark out, which likely helps them avoid nocturnal predators. That cell type lives in the retina, a multi-layered structure tucked behind the eyeball that’s crucial for vision as we know it. (Take a peek inside the colorful world of insect vision.)
It’s not yet clear whether the same enhanced sensitivity applies to humans or other animals. But understanding these kinds of peculiarities about how vision works is crucial for developing sensitive retinal prosthetics.One of the things you’d like to know to make those prosthetics work really well is, for any arbitrary visual scene you might look at, what pattern of signals are generated in the brain?” says study coauthor Greg Field, a neurobiologist at Duke University.
“If you can answer that question for any scene, then you know how to electrically stimulate the [prosthetic] retina to produce that pattern.”
Dark Motion
Assembling a visual image is a massively complicated process, one that requires cells in the retina to take in loads of data on contrast, color, movement, and orientation. As information from each cell type comes in, it’s transmitted to the brain, which performs an immense amount of parallel processing to put the generate a coherent scene—literally in the blink of an eye. (Find out why astronaut eyes get deformed in space.)
Field and his team wanted to find out how all that processing changes as light levels vary. In particular, they’re studying how a subset of motion-sensitive cells behaves across light conditions, from bright sunlight to pale moonlight.
In normal circumstances, scientists do this by removing a mouse’s retina and placing it over an electrode array that records which cells are activated by various types of visual stimuli. In a dish, the mouse retinas can survive for hours, responding normally to visual inputs. The team then shows the retinas-in-dishes a variety of movies under different lighting conditions and looks for differences in activation patterns.
nationalgeographic.com