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Our eyes have a built-in night vision, say scientists who have discovered that to see under the light of stars and moonlight, the retina modifies both the software and the material of its light-sensitive cells.
Retinal circuits considered immutable and programmed for specific tasks are adaptable to different lighting conditions. However, scientists have now identified how the retina is reprogramming for low light.
"To see under the starlight, biology had to reach the limit of seeing an elementary particle of the universe, a single photon," said Greg Field, an assistant professor at Duke University in the United States. United.
The results, published in the journal neuron, show that reprogramming occurs in movement-sensitive retinal cells. Even in the best lighting conditions, identifying the presence and direction of a moving object is essential to the survival of most animals.
Motion-sensitive cells
However, motion detection with a single reference point does not work very well. Thus, vertebrate retinas have four types of motion-sensitive cells, each specifically responding to a movement that is up, down, right or left.
In humans, these directional neurons account for about 4% of the cells that send signals from the retina to the brain. In a study with mouse retinas conducted under a microscope equipped with night vision eye pieces in a very dark room, the researchers found that retinal cells sensitive to upward movement change behavior under low light conditions.
The "up" neurons will fire as soon as they detect any movement, not just upwards. When there is much less light available, a weak motion signal from the up neurons, coupled with a weak signal from any of the other directional cells, can help the sensory movement of the brain.
Perception of loss of motion is a common complaint in human patients with severe vision loss. Field said that this discovery regarding the adaptability of retinal neurons could help design implantable retinal prostheses in the future.
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