The Amazing Brain of Blind People

Blindfold a sighted person for one hour and the brain has already changed during this time. Activity in the Visual Cortex was then measured during tasks such as hearing or feeling. This effect died out after the blindfolds were removed again.

Blindness

I learned some interesting insights about the brains of blind people in the book “Livewired” by David Eagleman and want to share them with you. Let’s go!

There are two types of blindness, neuroscientifically speaking. First: when the sensory input is broken and the second: when the processing part is broken. Blind does not necessarily mean complete darkness. But here I will consider blind people who can only see complete darkness.

No Sensory Input

The eye does not work. Mostly due to a disease, accident or a genetic defect. What can be done?

There are many studies on the subject, where blind people have cameras mounted on their heads and these cameras have passed on their data to the brain. How?

There are several variations that have worked. In one, haptic feedback is passed to the tongue. The shape and size of the object in front of the person is translated from video into touch in form of electrodes displaying the image in lower resolution on the tongue. This sensory information is then being processed by the Somatosensory Cortex first. The brain area processing touch. But after some practice, the brain learns that these touches on the tongue are information of the space around the body. The Visual Cortex gets active and now processes touch information. Then the person actually can see something, at least dimly. It looks to them like looking with the eyes. Like sighted people do. Only much less. You can find some videos on YouTube about this approach as well.

Another solution was found with a patient, where information from a camera was projected onto a chip on his retina. This chip emitted electrical impulses along the optical nerve, which the brain then recorded and processed. This person was able to see dimly with it.

In both cases. The more the patients practiced with the devices the better their vision became.

The Plasticity of the Brain

We saw that the Visual Cortex quickly takes over tasks for other kinds of sensory processing. Like touch or hearing. The neurons from the Somatosensory Cortex or Auditory Cortex send their information to the Visual Cortex. Thus, even with very fine touches on the tongue (or forehead or back; there are lots of options), one can map the environment. Differentiating between large, small and distant and near objects.

But this does also work for any other kind of sensory information. For all kinds of hearing, touching and smelling the visual cortex gets involved as well. The Somatosensory and Auditory Cortices (and other areas) expand their territories into the idle Visual Cortex.

This is also a reason why blind people can hear or touch so much better than sighted people. They simply have more brain capacity to process these sensory information since there is no information coming in from the eyes.

Thus some blind people are able to use echolocation for navigating in a room like a bat.

Interchangeability

Is every area of the brain predestined for a single task? As we have seen: No, the areas of the cortex are interchangeable. For example, scientists once implanted part of the Auditory Cortex into the Visual Cortex in an animal and it processed visual stimuli. But with some downsides. Cortex areas are not very good at processing ‘foreign’ information.

This is due to the fact that the brain is very changeable, but also only up to a certain degree.

The main nerve cables in brain are laid in us very early. Which is why blindness is best compensated the younger you are. Because newborns have a still very unformed brain, it is very good at compensating for non-functioning areas in the brain. Check out the story of Matthew who lives with only half a brain.

This is also one reason why humans have spread so quickly and successfully across the planet. They are incredibly adaptable to the environment and have the most cortex mass of all animals.

Damage to the Visual Cortex

So the Visual Cortex processes information about the world around the body. Regardless of the pathway the information comes from. Whether touch, vision or hearing. But what happens when the Visual Cortex fails due to a stroke, tumor or disease? What then?

People with damage to the Visual Cortex from surgical removal, tumor, disease or injury have blindness in a variety of forms. They may be unable to see in one eye, unable to see parts of the field of vision, or unable to recognize objects as such.

But what happens when the Visual Cortex fails?

Not all visual information is passed on to the Visual Cortex. Some is also processed in the limbic system. The ancient part of the brain.

But what happens in the limbic system is a bit too much for this article for now. More about that in another article ;)

I’m looking forward! See you next time