Biology textbooks say that the eye uses one type of photoreceptor cells, called cones, for color vision and another type, called rods, for black and white vision. However, a new study uncovers a circuit of nerve cells in the eye allows mice (and maybe also humans) to see colors using an entirely different mechanism—one that involves both rods and cones.
Previously, color vision was thought to involve a comparison of the signals received from different types of cones—photoreceptor cells in the eye that are sensitive to color. Rods, a different type of photoreceptor cell, were thought to be used only for colorless vision in very dim light.
In a new study, researchers from Caltech find that in the mouse retina, the perception of color can result from a circuit of cells in the retina that relies on signals from both rods and cones.
The work, done in the laboratory of Markus Meister, professor of biological sciences, shows that a neuronal circuit in the mouse retina responds to different wavelengths of light and allows the rods and cones to function together. The circuit enables the mice to perceive color, even in dim light when the cones are not sensitive enough to make their own detections.
To study the circuit’s significance in nature, the researchers took photographs of various materials that would appear in a mouse’s natural environment using a specialized filter that captured only the particular wavelengths of light that would be visible via this system. Their findings suggest that this method of color vision may help mice find food and detect territories marked by other mice—a form of social communication—even in the dim light of nighttime.
The researchers find that the same circuit exists also in the human eye, and can possibly explain some mysterious aspects of human color vision—for example, how objects in dim light have a blueish cast.
“Color has intrigued scientists, artists, and poets throughout human civilization, and this paper adds to the understanding of how this quality of the world is perceived,” says Meister.
These findings appear in the journal Nature.