When lights are dim or absent, animals tend to use their night vision to adjust to the low light and visualize their path and their prey. They need this to escape predators and protecting themselves. The little amounts of photons available are picked up by the eyes to detect what lies in front of them.
Researchers at Duke University in Durham, North Carolina, have now found that mice have a special kind of night vision that is associated with motion. They speculate that this novel mechanism might be found in other animals as well. The results of this study appear in the latest issue of the journal Neuron.
The researchers noted that there is a special type of cell within the layers of the retina that is more sensitive to movements when the lights are dim or very poor. Study co-author Greg Field, a neurobiologist at Duke University said that this understanding could pave the way for developing retinal prosthetics for the visually impaired. He explained that in low light conditions a pattern of movement might all be that is necessary to get the bearings. This might be helpful while making retinal prosthetics for the visually impaired. They could transform the pattern of movement into an electrical stimulus for the brain to detect, he explained.
During normal vision the light falls onto the retina and the retina differentiates between colours, depths, textures, orientation and movement to detect the object or path in front of the eyes. Each of the cells sends in messages to the brain that needs to work at super-speeds to process the information in parallel to bring out a coherent image or scene for the brain to understand. As the light levels reduce these cells begin to process the information in a different way to optimize vision. The team looked at how this happens.
For this study they took retina from dark-adapted mice who were accustomed to darkness for 12 hours. They extracted or dissected out the mouse retina while it was still in the dark while themselves wearing night-vision-goggles.
Field and his team took the mouse retinal layers in vitro and placed them over an array of electrodes. These can sense the activation of the cells to different visual stimuli. They exposed this retina to different movies at different light levels. Field says they could see what the retina feels when we watch a movie.
Graduate student Xiaoyang Yao in the process of exposing the retinas to increasing light conditions noted that in bright light the cells could detect upward movement while as the lights were dimmed the cells could detect movement in other directions as well including upward, downward, left and right. Field explained that these cells types seemed to act in low light conditions detecting motion. He added that this was essential for the mouse for example to detect the direction and movement of the owl that could be targeting it.
The team noted that the “up” cells or direction-selective ganglion cells (DSGCs) detected motion from all directions when in dark along with other three cell types which are also sensitive to motion. These are all electrically connected said Field.
More detailed studies in future could bring out a deeper understanding of this phenomenon say the researchers.