This work, appearing March 23 in Science, also suggests that when the first ancestral primate inherited a new type of photoreceptor more than 40 million years ago, it probably experienced immediate color enhancement, which may have allowed this trait to spread quickly.
"If you gave mice a new sensory input at the front end, could their brains learn to make use of the extra data at the back end?" asks Jeremy Nathans M.D., Ph.D., professor of molecular biology and genetics, neuroscience, and ophthalmology at Hopkins. "The answer is, remarkably, yes. They did not require additional generations to evolve new sight."
Retinas of primates such as humans and monkeys are unique among mammals in that they have three visual receptors that absorb short (blue), medium (green) and long (red) wavelengths of light. Mice, like other mammals, only have two; one for short and one for medium wavelengths.
In the study, the researchers designed a "knock-in" mouse that has one copy of its medium wavelength receptor replaced with the human long wavelength receptor, so both were expressed in the retina. The human receptors were biologically functional in the mice, but the real question was whether the mice could use the new visual information.
To address this question, the researchers used a classic preference test; mice set before three light panels were trained to touch the one panel that appeared to differ from the other two. A correct answer was rewarded with a drop of soy milk.
To circumvent thorny issues related to the subjective nature of color perception -- everyone who has had a discussion as to whether the "green" they see is the same as t
Source:Johns Hopkins Medical Institutions