Boy Missing The Part Of His Brain Essential For Sight Mystifies Doctors - Because He Can Still See

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Rachel Baxter 07 Dec 2017, 15:53

In a bizarre never-before-seen case, a 7-year-old boy who lost the part of his brain essential for sight can still see.

The boy, referred to as “BI”, lost the primary visual cortex of his brain, which is necessary for vision, in early infancy. This was due to a rare condition called medium-chain acyl-Co-A dehydrogenase deficiency.  

The visual cortex is responsible for the various sensations that create our visual experience of the world. The neurons of the primary visual cortex, absent in the boy's brain, are incredibly sensitive to things like the orientation of a contour and the direction of motion. People who experience damage to their primary visual cortex suffer from a condition known as “cortical blindness”, which involves either a partial or total loss of sight. 

Therefore, the fact that BI has retained normal vision – apart from being very short-sighted – is unheard of. A group of researchers, led by Iñaki-Carril Mundiñano from Monash University in Melbourne, Australia, decided to investigate. They presented their findings at the annual meeting of the Australasian Neuroscience Society in Sydney.

They ran a number of tests only to find that BI could name objects, identify colors, and discriminate between faces with no problems. He could reach out and grab blocks of different sizes, and could also tell if faces were happy, fearful, or neutral.

"Interestingly, BI has some difficulties identifying objects with a false colour, for example, a 'blue banana', but he has no problems with a yellow banana, we think he needs both colour and shape information to recognize an object," Mundiñano told IFLScience in an emailed statement. 

One downside of BI’s vision is his short-sightedness – he could only read an eye chart’s top letter if he was standing 3 meters (10 feet) away or closer.

Nevertheless, what is so unique about BI’s vision is that it is conscious. Some people with a damaged visual cortex are able to navigate an obstacle course despite being visually impaired, as if they can somehow still see unconsciously. This is known as “blindsight”.

However, BI happily plays soccer and video games. "The novelty here is that BI is entirely conscious of what he sees," said Mundiñano.  

So, how is this possible? Well, because BI was just a baby when he lost his primary visual cortex, it appears that the other parts of his brain compensated, adapting to provide sight. Sure enough, the team found that BI had more neural fibers between his brain’s pulvinar, which is involved in sensory signal control, and middle temporal area, which helps detect motion – two structures found close to the visual cortex.

The brains of newborns and infants are much more flexible and adaptable than adult brains. Mundiñano also told IFLScience that BI's level of vision would not be the same if he had lost his visual cortex during adulthood.  

Just yesterday, we reported on the intriguing case of a boy whose brain remapped itself in response to a hand transplant. This new research is just another example of the brain’s amazing capabilities, and how it continues to surprise us even today.

[H/T: New Scientist]

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