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It turns out that the eyes have a natural version for night vision. According to a recent study, to see under the light of the stars and in the moonlight, the retina of the eye changes both the software and the material of its light-sensing cells to create a kind of night vision .
Retinal circuits, previously considered immutable and programmed for specific tasks, are adaptable to different lighting conditions.
Greg Field, one of the researchers, said: "To see under the light of the stars, biology had to reach the limit of the presence of an elementary particle of the universe, a single photon .
The findings, which appear online early in Neuron, have shown 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. But detecting a movement with a single point of reference 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.
When an object moves precisely in one of these directions, this population of neurons fires strongly, Field said. However, if the motion is halfway between the top and the left, both cell populations will fire, but not so strongly. The brain interprets this type of signal as a movement going both up and to the left.
"For complex tasks, the brain uses large populations of neurons because a single neuron can only perform one," Field said.
In humans, these directional neurons account for about 4% of the cells that send signals from the retina to the brain. In rodents (a type of mammal), it is between 20 and 30% because motion detection is of vital importance for an animal that other animals really like to eat.
In a study with mouse retinas conducted under a microscope equipped with night vision eyepieces in a very dark room. The researchers found that retina cells that are sensitive to upward movement change their behavior in low light. The "up" neurons will trigger when detecting any type of 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 one of the other directional cells, can help brain movement as it interprets two directional signals as a motion that is something in between.
Perception of loss of motion is a common complaint in human patients with severe vision loss. Field said that this discovery of the adaptability of retinal neurons could help design implantable retinal prostheses in the future.
The study was published in the Journal of Neuron.
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