SAN FRANCISCO, Oct. 17 (UPI) -- Neuroscientists in California said Thursday they have discovered that when blood vessels in the retina block light coming into the eye, the shadows are imprinted into the brain.
The new, by chance finding reveals exquisitely intricate patterns created by these shadows -- at times only four cells wide. As a result, the corresponding images in the brain are represented "in a lot sharper detail than we thought," researcher Daniel Adams, a British visual neuroscientist at the University of California at San Francisco, told United Press International.
"We looked at one of the most studied regions in the brain" Adams said, "yet it is still possible to discover an entirely new anatomical feature there."
The nerve shriveling involved in making these brain shadows is the same process involved in the condition known as lazy eye, where one of the eyes does not match the movement of the other in tracking objects. As the researchers describe in the Oct. 18 issue of the journal Science, the new finding could help researchers learn how to rewire the brain before such damage becomes irreversible.
"This tells you the disease is caused by a normal process that is occurring in everyone to a different degree," Adams said.
The inside surface of the eye is criss-crossed with tiny arteries and veins thinner than a human hair. Blood is loaded with the oxygen-carrying biochemical hemoglobin, which eclipses images normally received by light receptor cells, creating nearly imperceptible blind spots.
Adams explained in the newborn brain, there is a competition for territory among the brain's nerve cells. Those involved in vision will shrivel, if not activated by light, in a use-it-or-lose-it scenario. "They're no longer plugged in," Adams said.
Adams was looking in the brain tissue of South American squirrel monkeys when, to his surprise, he saw a telltale pattern he recognized immediately from the eye.
"The most frequently asked question is, 'Why has this not been seen before?' The answer lies in the technique that we use to look at the cortex," Adams explained.
Although researchers conventionally look at the brain by cutting it into hundreds of slices and examining each individually, Adams and Horton carefully unwrapped the wrinkly gray matter of the brain and examined its large sections to see it as more of a single piece.
"This is rather like simply unfolding a road map to read it, rather than first putting it through a paper shredder and then trying to find your way by looking at the resulting narrow strips," Adams said.
Adams added humans and other monkeys possess strips of brain tissue connected to the eyes that are thick enough to obscure this pattern. Adams and co-researcher Jonathan Horton were examining the squirrel monkey because it reportedly did not have these "ocular dominance columns," which scientists believe are involved in binocular vision.
For years, scientists have believed images were represented in the brain rather coarsely. The fact that such delicate details are present show this "cortical map" is "at least three times more detailed than previously demonstrated," Adams said. "The true grain of the map is probably even finer, and may approach the discrete representation of individual cones in the retina."
Neurobiologist Dale Purves at Duke University Medical Center in Durham, N.C., said, "this is a piece of quite lovely work. It's a beautiful demonstration of how subtle differences in retinal activity can generate lasting effects. It's really amazing what they've shown."
(Reported by Charles Choi, UPI Science News, in New York)
