How Neuroplasticity helps the visually impaired and differently abled people

Q: How do blind people mange without their sight? What is the science behind it?

Krishna:  The brains of those who are born blind make new connections in the absence of visual information, resulting in enhanced, compensatory abilities such as a heightened sense of hearing, smell and touch, as well as cognitive functions (such as memory and language) according to scientific studies (1).

It is commonly assumed that the improvement in the remaining senses is a result of learned behavior; in the absence of vision, blind people pay attention to auditory cues and learn how to use them more efficiently. But there is mounting evidence that people missing one sense don't just learn to use the others better. The brain adapts to the loss by giving itself a makeover. If one sense is lost, the areas of the brain normally devoted to handling that sensory information do not go unused — they get rewired and put to work processing other senses.

The structural and functional neuroplastic brain changes occurring as a result of early ocular blindness may be more widespread than initially thought. Significant changes have been observed not only in the occipital cortex (where vision is processed), but also areas implicated in memory, language processing, and sensory motor functions.

On the MRI scans of those with early blindness, researchers observed structural and functional connectivity changes, including evidence of enhanced connections, sending information back and forth between areas of the brain that they did not observe in the normally sighted group.

These connections that appear to be unique in those with profound blindness suggest that the brain "rewires" itself in the absence of visual information to boost other senses. This is possible through the process of neuroplasticity, or the ability of our brains to naturally adapt to our experiences.

Even in the case of being profoundly blind, the brain rewires itself in a manner to use the information at its disposal so that it can interact with the environment in a more effective manner.

If the brain can rewire itself -- perhaps through training and enhancing the use of other modalities like hearing, and touch and language tasks such as braille reading -- there is tremendous potential for the brain to adapt.

The musical talents of Stevie Wonder and Ray Charles, both blinded at an early age, are cited as examples of blindness conferring an advantage in other areas.

Not only in the visually impaired, even the hearing impaired ones and other differently abled people show these extra ordinary senses.

Another study provides evidence of this rewiring in the brains of deaf people. The study, published in The Journal of Neuroscience, shows people who are born deaf use areas of the brain typically devoted to processing sound to instead process touch and vision. Perhaps more interestingly, the researchers found this neural reorganization affects how deaf individuals perceive sensory stimuli, making them susceptible to a perceptual illusion that hearing people do not experience.

These new findings are part of the growing research on neuroplasticity, the ability of our brains to change with experience. A large body of evidence shows when the brain is deprived of input in one sensory modality, it is capable of reorganizing itself to support and augment other senses, a phenomenon known as cross-modal neuroplasticity.

Understanding how the brain rewires itself when a sense is lost has implications for the rehabilitation of deaf and blind individuals, but also for understanding when and how the brain is able to transform itself. Researchers look to the brains of the deaf and blind for clues about the limits of brain plasticity and the mechanisms underlying it. So far, it appears that some brain systems are not very plastic and cannot be changed with experience. Other systems can be modified by experience but only during particular sensitive periods (as is the case with language acquisition). Finally, some neural systems remain plastic and can be changed by experience throughout life. Discovering factors that promote brain plasticity will impact several areas: how we educate normally developing as well as blind and deaf children; rehabilitation after brain injury; and the treatment (and possible reversal) of neurodegenerative diseases and age-related decline.

Research showed people born deaf are better at processing peripheral vision and motion. Some animal studies indicate both vision and touch play a role in altered cross-modal organization of auditory cortex, but until now, the evidence in humans has been limited.

In the research the deaf participants all showed greater activity in Heschl's gyrus in response to the air puffs and light, but their responses differed in degree. Those with the highest level of auditory cortex activity in response to touch also had the strongest response to the illusion. This supports the interpretation that the double-flash illusion is a functional consequence of the altered cross-modal organization in the deaf brain (2).

Footnotes:

1. Corinna M. Bauer, Gabriella V. Hirsch, Lauren Zajac, Bang-Bon Koo, Olivier Collignon, Lotfi B. Merabet. Multimodal MR-imaging reveals large-scale structural and functional connectivity changes in profound early blindness. PLOS ONE, 2017 DOI: 10.1371/journal.pone.0173064

2. https://www.scientificamerican.com/article/superpowers-for-the-blin...