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Updated: November 19, 2009 15:06 IST

How blind people fearlessly cross busy roads

ANI
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NO FEAR: Blindness causes structural changes that could help brain reorganize itself functionally, in order to adapt to a loss in sensory input. File Photo: V. Ganesan
The HIndu NO FEAR: Blindness causes structural changes that could help brain reorganize itself functionally, in order to adapt to a loss in sensory input. File Photo: V. Ganesan

Wondering how blind people appear to fearlessly navigate busy sidewalks or roads with just a cane? Well, UCLA researchers claim to have found the answer for you.

They have found that blindness causes structural changes that could help brain reorganize itself functionally, in order to adapt to a loss in sensory input.

Lead researcher Natasha Lepore, a postgraduate researcher at UCLA’s Laboratory of Neuro Imaging, has found that visual regions of the brain were smaller in volume in blind individuals than in sighted ones. However, for non-visual areas, the trend was reversed - they grew larger in the blind.

This, the researchers say, suggests that the brains of blind individuals are compensating for the reduced volume in areas normally devoted to vision.

“This study shows the exceptional plasticity of the brain and its ability to reorganize itself after a major input - in this case, vision - is lost,” said Lepore. The expert added, “In other words, it appears the brain will attempt to compensate for the fact that a person can no longer see, and this is particularly true for those who are blind since early infancy, a developmental period in which the brain is much more plastic and modifiable than it is in adulthood.”

During the study, researchers used an extremely sensitive type of brain imaging called tensor-based morphometry, which can detect very subtle changes in brain volume, to examine the brains of three different groups: those who lost their sight before the age of 5; those who lost their sight after 14; and a control group of sighted individuals. The analysis revealed that loss and gain of brain matter depended heavily on when the blindness occurred.

Only the early-blind group differed significantly from the control group in an area of the brain’s corpus callosum that aids in the transmission of visual information between the two hemispheres of the brain. The researchers suggest this may be because of the reduced amount of myelination in the absence of visual input. Myelin, the fatty sheaf that surrounds nerves and allows for fast communication, develops rapidly in the very young. When the onset of blindness occurs in adolescence or later, the growth of myelin is already relatively complete, so the structure of the corpus callosum may not be strongly influenced by the loss of visual input.

In both blind groups, however, the researchers found significant enlargement in areas of the brain not responsible for vision. For example, the frontal lobes, which are involved with, among other things, working memory, were found to be abnormally enlarged, perhaps offering an anatomical foundation for some of blind individuals’ enhanced skills.

The study appears online in journal NeuroImage.

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