It has long been theorized that individuals who lose one of their senses, or who have it significantly reduced, "make up" for this deficit with their other senses.
Even back in the 18th century, philosopher Denis Diderot wrote in awe about a blind mathematician who could distinguish real coins from fake ones just by touching them.
Although the brain's ability to compensate in response to a lack of visual stimulation is considered common knowledge, it was not until the 1990s and the advent of brain imaging that the theory could be confirmed. Today, the precise changes that occur in the brain are still being unpicked.
For instance, a 2009 study conducted at University of California-Los Angeles' Laboratory of Neuroimaging, uncovered some of the details. Using sensitive brain imaging techniques, they found that, in blind people, visual regions of the brain were small compared with those with normal sight, but nonvisual areas were larger in volume.
Although this marked a step toward understanding this process, the exact changes in the brain are still poorly understood.
Comparing sighted and blind brains
A recent study set out to chart these brain changes in more detail. The study was led by Massachusetts Eye and Ear researchers and is published today in PLOS One. For the first time, the team combines structural, functional, and anatomical brain changes and compares blind people's brains with those of people with normal sight.
To develop a picture of the brain changes that occur, the team used both diffusion-based and resting state MRI. In all, 28 participants took part in the study: 12 were either blind from birth or had become blind before the age of 3, and 16 participants had normal sight.
The scans of individuals with early blindness showed clear differences from the control scans of normally sighted participants, so changes in structural and functional connectivity could be measured.
Enhanced connections between specific parts of the brain were seen in the blind people that were not present in the control group. These observed differences surprised researchers:
"Our results demonstrate that the structural and functional neuroplastic brain changes occurring as a result of early ocular blindness may be more widespread than initially thought."
Corinna M. Bauer, Ph.D., lead author
Bauer, a teacher of ophthalmology at Harvard Medical School in Boston, MA, continues: "We observed significant changes not only in the occipital cortex (where vision is processed), but also areas implicated in memory, language processing, and sensory motor functions."
Neuroplasticity and blindness
These changes are due to neuroplasticity, which means that our brain can react and change in line with the environment it is interacting with. Therefore, the brain is able to rewire itself when visual information is not available.
The findings are fascinating, and the researchers also hope that they might eventually help to inform treatment. It might be possible to enhance the rehabilitation of people who have become blind by teaching them how to compensate for the lack of incoming visual information.
Lotfi Merabet, Ph.D., director of the Laboratory for Visual Neuroplasticity at the Schepens Eye Research Institute of Massachusetts Eye and Ear, explains:
"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."
Because the details of this plasticity in response to blindness are being viewed for the first time, it will be some while before they can become clinically useful. However, this marks a huge step forward in understanding.