With a bit of genetic manipulation, researchers have made it possible for mice to see in color, a development that scientists say may some day help people who have suffered brain injuries. VOA's Jessica Berman reports.
Zoologists say primates, such as humans and apes, are unique in the animal kingdom in that they see the world in a full range of colors. They possess three visual light sensors in their eyes that absorb light in three wavelengths - short waves, which detect shades of blue, medium waves for green colors and long waves for red colors.
In contrast, mice and other mammals have only two light sensors, one that absorbs blue light and another that absorbs green light.
Researchers at Johns Hopkins University in Maryland and the University of California in Santa Barbara wanted to see whether they could genetically engineer mice to see color the way primates do. They bred mice to contain a human sensor for red light, and the results were dramatic, according to Jeremy Nathans of Johns Hopkins, who is one of the study's lead investigators.
Nathans says the rodents' brains adapted immediately to this "simple genetic event," as he calls it, and the mice began to see the world in full color.
"This was instantaneous," he said. "That is, as soon as the new light sensor was present in the animal, that animal could take advantage of it."
Nathans says there was no long period of evolution as might be expected when an animal acquires a new trait.
So how does one test the vision of a mouse?
Nathans says laboratory mice were trained for thousands of hours to figure out a color test. Eventually, he says they learned how to do the test, and the genetically engineered mice were compared to normal mice in their ability to perform the test.
In the experiment, Nathans says the normal mice confined themselves to colors perceived by their blue and green vision sensors.
But a mouse that was genetically altered took a different path toward colors it perceived with the new photoreceptor.
"It walked over to the one that's different and it puts its nose up there. And if it's correct, then right above the little panel, the illuminated panel, we have a tube and, from that tube, a droplet of soy milk will come out," he explained.
Because the brains of the mice accepted the new light sensor so quickly, Nathans and colleagues are optimistic their work may some day benefit people who have suffered some form of brain injury.
"It would suggest there are ways for the brain to learn new skills, to change its intrinsic wiring, to recover function," he added.
An article describing the work is published in the journal Science.