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Man claims victory over handicap as brain retrains itself

By Catholic Online (NEWS CONSORTIUM)
April 18th, 2013
Catholic Online (www.catholic.org)

By any other standard, he shouldn't be able to see - or the way how most human beings see things. In an example of the adaptability of the human brain, a 28-year-old man known only as GB is able to see, in spite of his crossed optic nerves.

LOS ANGELES, CA (Catholic online) - Most of the time,  the optic nerves have a crossroads which are known as an optic chiasm which diverts sense data so that each half of their brains processes information from either side of their visual field.

"GB" was born without this crossover, meaning each half of his brain is forced to process information from his whole visual field.

Called achiasma, the condition means all the signals from his left eye end up in his left visual cortex and all the signals from his right eye end up in his right visual cortex.

Canadian neurologist Jodie Davies-Thompson, of the University of British Columbia, along with her colleagues is at a loss as to how his brain processes it.

Normally the left visual cortex deals only with the left side of visual space, while the right visual cortex deals with the right side. GB's brain, in each half must cope with the entire visual field, twice as much space.

As published in Neuropsychologia, Dr. Thompson and her colleagues reported that GB's brain has adapted by overlapping the two halves of space in GB's visual cortex.

The fMRI scans of GB's brain as published in their study, four colors are used to represent the four quarters of his visual field and the parts of his brain that light up in response to them.

The bottom and top of his visual field remain separately represented, as they would be in a normal person's brain. But there is a complete overlap between areas responding to bottom-left and bottom-right, as well as top-left and top-right.

More amazingly, GB's 20/80 score in an eye test - one quarter as good as a typical person, despite his congenital disorder, yet another instance of incredible adaptability of the human brain.

"This is a fascinating case report, and vision neuroscientists will find much to ponder here," Neuroskeptic remarks. "Still, what I'd love to know is how does it feel to have overlapping representations of the two sides of space?

"Does everything seem to be mirrored vertically? Does GB find it easier to tell objects apart when they're above and below the other, compared to side-to-side?"

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