What Blindsight Can Tell Us About The Architecture Of The Brain
    By News Staff | April 8th 2012 10:23 PM | 2 comments | Print | E-mail | Track Comments
    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.

    Zebrafish visual cortex
    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.

    Credit: Jon Baime, Science Nation Producer

    Ro observed what happened to other areas of Ai's brain during the instant he was blinded and a shape was flashed on the screen. While the blindness wears off immediately with no lasting effects, according to Ro, the findings are telling. "There are likely to be a lot of alternative visual pathways that go into the brain from our eyes that process information at unconscious levels," he says.

    Ro believes understanding and mapping those alternative pathways might be the key to new rehabilitative therapies. "We have a lot of soldiers returning home who have a lot of brain damage to visual areas of the brain. We might be able to rehabilitate these patients," he says. And that's something worth looking into.


    Gerhard Adam
    If I recall, there are two main separate visual pathways in the brain, and when one is damaged [as in blindsight]  the other is still functional, although there is no "conscious awareness" of what is being seen.  V.S. Ramachandran characterizes these as the "old" and "new" pathways, wherein it is only the "new" one that is associated with the type of conscious recognition we associate with sight.

    The "old" pathway also works in the vision system, but it is unconscious and therefore we aren't aware that we are seeing. 

    Clearly there are multiple pathways involved in vision [this isn't the first time this has been discussed], since they are involved in a variety of activities ranging from object recognition to coordination of movement in 3D space.

    Mundus vult decipi
    This seems like a tough experiment to pull off. How can the investigators be sure that the magnetic stimulation entirely wiped out all vestiges of the stimulus in the conscious pathway? One would expect that if some information was left, subjects might well do better than chance at identifying the stimuli, even while denying they saw anything. This dissociation of performance and report occurs all the time at threshold stimulus levels, where signal detection theory (Green & Swets) can ferret out and quantify performance ability, and explains subjects' reporting that they didn't see anything as a decision threshold effect. Perhaps the subjects see something, enough to identify the stimulus, but so unlike what they see without the magnetic stimulation that they say they didn't "see" the stimulus.

    In any case, good luck with it. I hope you've figured a clever way around this issue, and others which may crop up.