Unlike horses and eagles, whose eyes on the sides of their heads provide two different scenes, humans see a single, in-depth view.
In a report published in the Public Library of Science (PLoS) Biology and in the journal Cerebral Cortex, researchers from the Picower Institute for Learning and Memory at MIT claim that they have identified the gene that is responsible for melding images from two eyes into one useful picture in the brain.
"There are other instances in the brain where two different inputs have to be properly aligned and matched--such as auditory and visual projections to the midbrain that enable us to orient to sound," said lead author Mriganka Sur, Sherman Fairchild Professor of Neuroscience at the Picower Institute, and head of the Department of Brain and Cognitive Sciences at MIT.
"This is the first study to pinpoint a gene with this kind of job," he added. Binocular vision enables a person to perceive depth and carry out detailed visual processing. The images projected by each eye are aligned and matched up in brain regions called the visual thalamus and cortex.
The researchers have discovered that the genes Ten_m3 and Bcl6 have a key role in the early development of brain pathways for vision and touch. They say that Ten_m3 appears to be critical for the brain to make sense of the two disparate images from each eye. During the study, the researchers observed that in mice with the Ten_m3 gene knocked out, projections from their two eyes were mismatched in their brains. They say that the mice were blind even though their eyes worked normally, as each eye's projection suppresses the other.
The researchers also noted that the knockout mice could see again when the output of one eye was blocked at a molecular level. They say that one eye was able to function with the other eye's conflicting input shut down, though only with monocular vision.
"This is an amazing instance of 'gain of function' that proves immediately that the gene is directly responsible for creating matched projections from the two eyes," Sur said.
"There are reports of human visual conditions in which simply closing one eye allows a person to see much better. We believe that genes such as Ten_m3 are at the heart of these disorders," he added.
The National Institutes of Health, the Simons Foundation, and Australia's National Health and Medical Research Council supported the study.