A new research reveals that humans naturally have a night vision mode, which allows us to see the moon and the stars more clearly. According to Duke University scientists, our retinas change both the “software and hardware of the light-sensing cells.” We used to believe that our retinal circuits are unchanging and are already programmed for specific jobs. However, this fresh discovery suggests that it actively adapts to various light conditions.
Greg Field, an assistant professor of neurobiology and biomedical engineering at the university said in a statement, “To see under starlight, biology has had to reach the limit of seeing an elementary particle from the universe, a single photon… It’s remarkable at night how few photons there are.”
How We Identify Motion
The study published in Neuron shows that the adjustment happens in motion-sensitive retinal cells. Even in bright lighting, spotting the existence and course of a moving body is a primary survival instinct of animals.
Identifying motion with a single point of reference, however, doesn’t work as accurately. For that reason, the motion-sensitive retinal cells of vertebrates are divided into four sections, each reacting to a direction of movement that is the right, left, up, and down.
So when an object is moving halfway across our vision, between up and left, populations of cells for both parts will fire. Yet, the reaction doesn’t happen as strongly for neurons on only one side. That’s the mechanism of the human night vision.
Our Brain On Complex Tasks
Because a single cell has limited capabilities, Field said that the brain uses a large number of neurons to perform complex tasks. He explained that in humans, these directional neurons make up for about four percent of the cells that receive and deliver signals to the brain. The case is much higher for rodents, where it is estimated between 20 and 30 percent. This fact doesn’t come as a surprise since wildlife relies heavily on this ability, especially those which prey other animals.
With night vision eyepieces in a dark room, researchers examined the retinas of a mouse under a microscope. They used an electrode array to count each individual firing of neurons in the retinas. As a graduate student working at Field’s lab, Xiaoyuang Yao found out that the retinal cells were sensitive on shifts in upward motions in low light. Those “up” neurons react whenever some kind of movement is sensed, not just when “upward” movements are registered.
When there is little light, any small movement detected by the “up” cells mixes with the signals from other directional neurons. Those visual cues help the brain perceive motion, which is similar to how two directional signals are noted as movement.
Impact On The Future of Vision Loss Treatment
Loss of motion perception is one of the most common complaints in patients with severe vision loss. Field hopes for further study into the flexibility of retinal neurons and how they work in our natural night vision. In the future, this discovery may allow scientists to design an implantable retinal prosthetics to treat vision problems.
