A new study has found that our retinal circuits give us natural night vision which enables us to see the night sky and stars clearly. Our retinas change both the “software and hardware of the light-sensing cells,” which work together so we can see in starlight and moonlight.
The new study published in Neuron suggests the retinal circuits in our eyes are adaptable and can adjust themselves to different light conditions, and a team of scientists discovered how the retina reprograms itself.
“To see under starlight, biology has had to reach the limit of seeing an elementary particle from the universe, a single photon,” Duke University Assistant Professor Greg Field said in a statement. “It’s remarkable at night how few photons there are.”
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When an object is moving in a certain direction, neurons in the eyes try to detect it. If the motion of an object is about halfway across our vision, between left and up, populations of neuron cells for both parts will fire, but not as strongly as those on only one side would fire. That’s how our natural night vision works.
“For complex tasks, the brain uses large populations of neurons, because there’s only so much a single neuron can accomplish,” Field said.
According to Field, in humans, directional neurons account for roughly 4% of the cells that are receiving signals and sending them to the brain. In rodents, it’s estimated to be between 20% and 30%. Motion detection is of utmost importance for animals, especially those which eat other animals.
Scientists studied the retinas of a mouse under a microscope with night vision eyepieces in a dark room. They placed a sample of a mouse retina on an electrode array that measures the individual firing of neurons at once. Xiaoyuang Yao, a graduate student working at Field’s lab, discovered that the retinal cells were sensitive on upper movement changes in low light. Those “up” neurons fire whenever some kind of movement is detected, not just when “upward” movements are registered.
“Xiaoyang’s insight was to go and look at what these cells do in day and night,” Field said. “She noticed a difference and wondered why.”
When a retina is exposed to only a little light, a small signal of motion coming from the “up” neurons is combined with the signals from other directional cells. Those signals help the brain feel movement, which is similar to how two directional signals are recognized as motion.
When there is severe vision loss in human patients, loss of motion perception is considered the most common problem people experience. Field said if more research is conducted into the adaptivity of retinal neurons and how they work in our natural night vision, scientists could be able to design implantable retinal prosthetics to treat those conditions in the future.