ASL or English? Primary language learned shapes brain matter
If you use American Sign Language (ASL) to communicate and ever needed proof that your brain works differently than others, here it is:
Researchers at the Georgetown University Medical Center (GUMC) and the Center for Visual Language and Visual Learning at Gallaudet University have discovered differences in the brain anatomy between deaf people who grew up learning only English versus those who grew up learning ASL.
“We found that our deaf and hearing participants, irrespective of language experience, differed in the volume of brain white matter in their auditory cortex. But, we also found differences in left hemisphere language areas, and these differences were specific to those whose native language was ASL,” said Guinevere Eden, Ph.D., GUMC’s center director, in a press release.
According to the study, published April 16, 2014, in The Journal of Neuroscience, certain areas of the brain in native ASL communicators had denser gray matter than in those who grew up only learning English. Prior to the study, researchers had focused mainly on comparing the brain make-up of hearing individuals and that of deaf individuals without distinguishing between English speakers and those who use ASL to communicate.
“Prior research studies comparing brain structure in individuals who are deaf and hearing attempted to control for language experience by only focusing on those who grew up using sign language,” said Olumide Olulade, Ph.D., the lead author of the study and post-doctoral research fellow at GUMC, in the press release. “However, restricting the investigation to a small minority of the deaf population means the results can’t be applied to all deaf people.”
Differences in cognitive development impact brain structure in people of all backgrounds, not just the deaf population. But by limiting research on the impact of deafness in brain development to those individuals who learned sign language, a significant portion of the deaf population was left unstudied. According to GUMC, 95 percent of deaf children are born to hearing parents, so examining native deaf English speakers is an important component of hearing loss research.
The study examined four groups of 15 individuals: hearing native ASL communicators, deaf native ASL communicators, hearing native English speakers and deaf native English speakers. The researchers found distinct differences in the volume of gray matter, which is responsible for muscle control and sensory perception, and white matter, which is responsible for transmitting signals throughout the brain, in each of the four groups. The findings correlate to the differences ASL communicators and English speakers (lip readers), as well as those who can hear and who exhibited differences in their auditory complex.
While the researchers didn’t draw many conclusions from the results, the distinctions are a step in closer to understanding how development impacts the brain, especially in those who grow up with hearing differences. Each side of the brain has separate responsibilities: the right side of the brain is largely responsible for spatial abilities and visual imagery, while the left side dominates language skills. Differences in brain anatomy correspond to differences in auditory and language development in both the hearing and deaf populations. Understanding why some deaf people have more gray matter than others and why will inform hearing loss studies going forward.
Scientists are making strides in neurological research every day, bringing us closer to understanding how the brain works and what impacts its development. New discoveries could one day lead to the prevention of many forms of hearing loss, or at least to the improvement of circumstances surrounding hearing loss. If experts understand how certain environmental and sociological factors affect brain development, they can educate parents with deaf and hard-of-hearing children on the best way to raise them. Cognitive development is a major concern in children with hearing loss, who are often vulnerable to falling behind their hearing peers.
However, with a better understanding of brain development, teachers, parents and employers can better accommodate people with hearing loss and adapt a world centered around hearing individuals to be a little more hearing loss friendly.