Supersensors: How the loss of one sense impacts the others

Would you ever voluntarily give up one of your senses? Turns out, the answer for an ever-increasing number of people is yes (albeit only temporarily). Novelty concepts such as dining in the dark have risen in popularity over the past decade; restaurant-goers frequently give up their sense of sight as a way to have a “heightened” mealtime experience1. Most of these diners believe that their temporary blindness intensifies their other sensations - but how would a more permanent loss of sensation affect the ways we perceive our world?

For most of us, we can barely even imagine what something like blindness would feel like. We have grown accustomed to our world’s sights, sounds, and smells; each is integral to the way we experience the world. In what ways, though, do people who lack one of these senses experience the world differently?

OUR SENSES AND THE BRAIN

Our brains typically organize themselves based upon function: we have the auditory cortex for sound, the visual cortex for sight, the olfactory bulbs for smell, and so on. For the vast majority of us, the sensory inputs we receive from our environment travel through the nervous system to their respective areas in the brain. Many people, though, are born without the ability to do things such as see or hear. Yet, these specialized areas of the brain for each sense do not simply become obsolete.

REWIRING THE BRAIN

Past research has shown that in individuals who are born blind or lose ther sight early in their childhood, the brain “rerouts” the normal sensory pathways such that non-visual information is sent to the visual cortex. For example, visual information is usually sent to a specialized area of cortex where it is used to determine the spatial arrangment of objects in the environment. However, in individuals who have been blind since childhood, this area of visual cortex instead receives sound and touch information. In this way, the blind are able to use their other senses to form a picture of their environment in the same manner that those with sight do2. The unaffected senses take up the responsibilities of the affected sense, so to speak. But how does the brain achieve this reorganization of itself?

 Fig. 1 In the absence of visual input, the visual cortex is used to process non-visual sensory information (Figure taken from Merabet et al., 2005).

Fig. 1 In the absence of visual input, the visual cortex is used to process non-visual sensory information (Figure taken from Merabet et al., 2005).

THE BRAIN IS PLASTIC

The brain has a unique characteristic known as “plasticity.” Imagine that you are planning your commute to work in the morning and you discover that road you usually take is closed due to construction. What do you do? You will most likely take a different route that still gets you to the same place; you’ll take a detour. This is similar to how the brain achieves this remodeling ability. When certain pathways are “closed off,” the brain is able to take a detour of sorts. New connections are always forming, old or unused connections weaken over time; thus, the brain is always morphing and responding to the environment and the signals provided to it3. Since certain signals will not be reaching the brain, the other senses will expand out of their usual locations in the brain and into the area of the missing sense. Thus, these senses are overrepresented proportionally in people who lack a certain sense.

LOSE A SENSE, IMPROVE ANOTHER

Now it becomes clear how the blind, for example, are able to isolate sounds with greater acuity or have the ability to experience their food in a way the rest of us usually do not. The lack of sensory input causes a sequence of events within the brain that allows the other senses to take over the roles left unoccupied. So, the next time you go out to dinner, try closing your eyes. Though you may be in the dark, you may just find that your sense of taste and of smell light up in ways you’ve never experienced.

Sources:

[1] Storrs, C. (2016, June 9). Was Mom right? Are your eyes 'bigger than your stomach'?http://www.cnn.com/2016/04/08/health/eating-without-seeing-dining-in-dark/

[2] Renier, L.A., Anurova, I., De Volder, A.G., Carlson, S., VanMeter, J., Rauschecker, J.P. (2010). Preserved functional specialization for spatial processing in the middle occipital gyrus of the early blind. Neuron 68, 138–148.

[3] Johansson BB (2000) Brain plasticity and stroke rehabilitation: the Willis lecture. Stroke 31:223–230.

[4] Merabet, L., Rizzo, J., Amedi, A., Somers, D., Pascual-Leone, A. (2005). What blindness can tell us about seeing again: merging neuroplasticity and neuroprostheses. Nature Reviews Neuroscience 6, 71-77. | doi:10.1038/nrn1586

[Image 1] 4U King Lear. Blindness/Sight. Retrieved from https://sites.google.com/site/4ukinglear/home/blindness-sight