According to our new study, we could have our own natural "night vision"

It's really amazing to see how much we can see, even when the objects only diffuse very few photons, for example by starlight or moonlight. A new study offers a possible explanation, suggesting that mammals and other vertebrates rewire both "software" and "hardware" of light-sensitive cells to provide a kind of natural night vision.

S & # 39; adapt to black

Until not so long ago, retinal circuits were considered rigid and intended only for specific tasks. However, the results suggest that in mice at least some retinal cells are reprogrammable.

In order to assess the presence and direction of an object in motion – a critical ability for prey and predators – vertebrates have developed four types of motion-sensitive cells, each responding to a specific type of motion : up, down, right and left.

When an object moves in one of these directions, the corresponding neuron population fires strongly. If the movement is halfway between the top and the left, the two populations of neurons will fire, but not as strongly as in a clear direction of movement.

"For complex tasks, the brain uses large populations of neurons because there is only one neuron to perform," said Greg Field, an assistant professor of neurobiology and biomedical engineering at Duke University.

Previously, studies have shown that in humans, these directional neurons account for about 4% of cells that send signals from the retina to the brain. In rodents, this ratio is between 20% and 30%, because they can make the difference between a danger of leakage or consumption.

"Many animals choose to feed at night, probably because it's harder for predators to see it," Field said. "But of course, nature is an arms race. Owls and cats have developed highly specialized eyes to see at night. The prey has changed what they have to survive.

Researchers at Field's laboratory studied mouse retinas under a microscope equipped with night vision eyepieces in a very dark room. Remarkably, they discovered that "up" neurons began to fire when they detected all types of movement, not just upwards.

The extra firepower of the neurons in height, coupled with signals from any other directional cell, helps the brain to detect motion when light is insufficient.

It is not yet clear why only "rising" cells become movement generalists in low light conditions. One possible explanation is that the most important direction for a prey animal is to spot a predator that may be standing on the approach.

Whatever the case may be, this is the first study that shows that the eye and the brain are modifying their movement calculation to facilitate vision during the night.

"We have learned that large populations of retinal neurons can adapt their function to compensate for different conditions," Field said.

It is likely that other types of circuits are adaptable. There are 50 types of amacrine cells – interneurons in the retina – but we only know 20% of these cells.

In more practical terms, the findings could help researchers design implantable retinal prostheses. Misperception of movement is one of the most important symptoms of severe vision loss.

The results appeared in the journal Neuron.

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