The human brain is an astonishing organ, capable of rewiring itself in response to changes in its environment. This phenomenon is called neuroplasticity! [1] You might have come across this term in one of our other blogs, but today we’ll be focusing on one really fascinating consequence of this phenomenon. The way the brain adjusts when a sense, like sight or hearing, is lost is among the most amazing illustrations of this process. Deprivation of senses can cause significant alterations in brain activity that alter our understanding of and interactions with the outside world [2], and that’s exactly what we will be looking at today!
The brain's capacity to realign itself by enlisting regions normally utilized for a missing sense to assist other, intact senses is known as crossmodal neuroplasticity. This is most evident in individuals who are blind or deaf. The brain does not simply shut down when one sense stops providing information. Rather, to make up for the loss, the brain's processing centers for the remaining senses may grow and become more sensitive. [3]
For example, studies reveal that blind people frequently have better tactile sensitivity and sound localization skills, whereas deaf people may have better peripheral vision. The brain areas that would normally process the absent sensory data have changed as a result of these adjustments. For instance, in blind people, certain areas of the visual cortex may begin to process touch or sound information.
Although the brain is remarkably adaptive to sensory loss, neuroplasticity does not necessarily translate into improved function. While compensatory behaviors can emerge, neuroplasticity can also result in maladaptive modifications [4], especially when attempts are made to regain lost sense. For example, if a person regains sight after being blind for a lengthy period, the brain's visual processing pathways may have gotten repurposed for other senses, making it harder for the brain to properly reintegrate visual information. This may make it difficult for the person to comprehend what they see, even in cases where their eyesight is flawless. Therefore, neuroplasticity may pose challenges to rehabilitation efforts and make the process of regaining sensory function more difficult.
Research on both humans and animals has provided us with a great deal of information about how the brain adjusts to sensory loss [5]. Neurons in brain regions linked to other senses can proliferate as a result of sensory deprivation, as demonstrated by animal models such as congenitally deaf mice and visually impaired cats. For instance, cats who are blind or visually impaired show a significant improvement in sound localization, and neurophysiological research shows that parts of the brain usually used for visual processing start to specialize in auditory tasks. [5]
Similar patterns have been found in human research. According to a study done on blind people, the brain's typical vision-related regions are also used to comprehend touch and sound. Imaging methods that demonstrate greater activity in the visual brain when blind people perform tasks like reading Braille lend credence to these findings.
However, it's not just the loss of a sense that drives these changes. Development, experience, and timing are equally important factors. In contrast to sensory loss that occurs later in life, early sensory deprivation, such as congenital blindness, results in distinct kinds of neuroplastic alterations. [6]
One query that comes up is the precise process by which certain brain regions are repurposed. One hypothesis is that the brain takes advantage of pre-existing connections between distinct sensory regions [7]. Anatomical research has shown that the visual, auditory, and somatosensory domains are directly connected in both humans and animals. These already-existing connections may become "unmasked" and stronger in the event of sensory deprivation, enhancing the brain's ability to integrate information from other senses.
Increased connection between the somatosensory and visual regions of the brain, for instance, was discovered in studies with early blind people, demonstrating how these crossmodal interactions can take place even in the absence of visual input. [8]
The brain's capacity for adaptation in the wake of sensory deprivation creates new therapeutic opportunities. It does, however, also come with difficulties. As discussed earlier, this same neuroplasticity can impede attempts to restore the lost sense, even if some people may acquire improved ability in their surviving senses.
In order to help in recovery, researchers are looking for techniques to direct changes in the neuroplastic matrix. One day, non-invasive brain stimulation methods, for example, might be used with conventional treatments to promote positive neuroplasticity and inhibit negative changes. [4]
The conventional belief that losing senses results in a lower quality of life is called into question by the brain's capacity to rewire itself in response to sensory deprivation. Rather, sensory deprivation can lead to remarkable adaptations that allow people to make use of their remaining senses in new and powerful ways to navigate the environment.
As we begin to comprehend the mechanics behind these alterations, it becomes obvious that sensory deprivation is not only about loss. Instead, it's about how the plastic organ that is the brain adapts to survive in a multimodal environment.
- Varun Kheria, Science Communicator, ARISA Foundation