According to a pioneering study conducted by the Oregon State University College of Science, small freshwater zebrafish have highlighted how the brain of humans who are congenitally deaf will rewire itself and affect how they learn. This is the first step in analyzing congenital deafness further than just the sensory hair cells inside the ear. Studies such as OSU’s are paving the way to understanding how this condition that affects 1 in every 2,000 births is altering the way those in the deaf community think, learn, and live their lives.
Congenital Deafness, according to the American Speech-Language-Hearing Association (ASHA), is simply described as hearing loss present at birth, but the condition is far from simple. It can include hereditary hearing loss or hearing loss due to other factors either in-utero or at the time of birth. Multiple factors are responsible for congenital deafness, making each case unique and complex depending on genetics or environmental factors.
Some factors that may result in congenital deafness in newborns include:
Genetics may also be responsible for hearing loss in newborns, as genes that cause hearing loss can be carried by one or both parents, even if they have healthy hearing. This may result in a genetic syndrome with hearing loss as a symptom such as:
Led by Colin Johnson, an associate professor of biochemistry and biophysics at OSU’s College of Science, the research team behind OSU’s groundbreaking study had concluded: “The profound deafness-causing mutation of the otoferlin protein also alters the growth and wiring of neurons crucial to the nervous system.” This conclusion is thanks to an unlikely model, the small freshwater zebrafish. With a focus on the workings of the otoferlin protein, whose unique role within the cochlea is to encode sounds in the fragile sensory hair cells, researchers used zebrafish after finding that they were “highly similar to humans at molecular, genetic and cellular levels”. Previous studies had found that the otoferlin protein was too large to study comfortably in humans, prompting Johnson and the team at OSU to find an alternative model.
In fish with the otoferlin gene excluded, researchers had witnessed an alteration in neuronal genes involved in the growth and wiring of neurons, which when applied to human models suggests that the brains of people born deaf rewire themselves in ways that affect how these people learn.
“If you grow up without that protein, it’s not just a matter of throwing the gene back in. If you’re born deaf and grow up deaf, it seems the physical wiring of your brain is a little different,” concluded Johnson, further expressing the need to “go beyond looking at those hair cells and look at the brain itself. Does the brain process information differently? That’s one area we need to think about.”