Everyone has heard of hindsight - where the context of past events is much clearer in memory than they were at the time - but a new study of the blindsight phenomenon, where a person is cortically blind yet they can still discriminate visual information without any awareness, could make the architecture of the brain a lot clearer.
Toward that end, Tony Ro, a neuroscientist at the City College of New York, is artificially recreating blindsight in his lab. Sound scary? Just wait.
Injury or damage to the brain's visual cortex causes blindness but it may be possible to train the brain to see anyway, according to Ro. It just involves parts of the brain we aren't aware we use. To test that, Ro uses volunteers who are willing to be temporarily blinded by having a powerful magnetic pulse shot right into their visual cortex. The magnetic blast disables the visual cortex and blinds the person for a split second. "That blindness occurs very shortly and very rapidly--on the order of one twentieth of a second or so," says Ro.
Between alerting us to danger and allowing us to spot prey, vision keeps many animals, including humans, alive. The complexity of the neural network that supports vision has long baffled scientists. Claire Wyart in Ehud Isacoff's lab at the University of California at Berkeley and Filo Del Bene at Herwig Baier's lab at the University of California at San Francisco have been able to follow entire populations of retinal and brain cells in their test animal--the zebrafish larva--and solve some of the mysteries of the neural circuit that underlies its vision. Using a newly developed, genetically encoded, fluorescent reporter of neural activity developed by Loren Looger at the Howard Hughes Medical Institute's Janelia Farm Research Campus, Wyart and Del Bene have been able to follow how large and small visual cues translate into electrical activity in a region of the zebrafish's brain. The researchers have revealed that a large visual stimulus covering the entire field of vision (such as large floating debris, or another zebrafish) results in low output neuron activity. Credit: Zina Deretsky, National Science Foundation
Science Nation correspondent Miles O'Brien visited Ro's lab in the Hamilton Heights section of Manhattan where volunteer Lei Ai was seated in a small booth in front of a computer with instructions to keep his eyes on the screen. A round device was placed on the back of Ai's head. Then, the booth was filled with the sound of consistent clicks, about two seconds apart. Each click was a magnetic pulse disrupting the activity in his visual cortex, blinding him. Just as the pulse blinded him, a shape, such as a diamond or a square, flashed onto a computer screen in front of him.
Ro told O'Brien that 60 to nearly 100 percent of the time, test subjects report back the shape correctly. "They'll be significantly above chance levels at discriminating those shapes, even though they're unaware of them. Sometimes they're nearly perfect at it," he added.
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