Aphasia is a debilitating condition of the brain that impairs the use of both spoken and written language. Around 1 in 250 in the U.S. live with the problem and it can affect people of any age, race or gender. Sufferers may have difficulty producing, ordering and understanding everyday words. Now the authors of a study in the United Kingdom say they have revealed the "evolutionary roots of language in the brain." Their results — published in Nature Communications — could mean a clearer picture of how we learn, lose and regain language.
The team from Newcastle University in the UK was led by Dr. Ben Wilson and Professor Chris Petkov. Using a special brain imaging technique to explore cerebral activity in both humans and monkeys the scientists say they have identified the ways in which the brain has evolved to allow us to identify "the orderliness in sequences of sounds." The new research, they say, will help our understanding of how we learn language — as well as how it is lost by people who suffer aphasia after a stroke or as a result of brain tumors or dementia.
The area in the left frontal lobe of brain — known as Broca's area — has long been understood to be the center of expression and motor control for language use. Damage to this area can result in speech with a "telegraphic character" — a slow, labored delivery of only the nouns, verbs and important adjectives. Now the Newcastle team says they have identified an area at the front of the brain that recognizes when sequences of sounds appear to be in legitimate order or in an unexpected, illegitimate one.
"Young children learn the rules of language as they develop, even before they are able to produce language," Petkov says, "so we used a 'made-up' language, first developed to study infants, which our lab has shown the monkeys can also learn." The team played the human and monkey participants example sequences from the made-up language that demonstrated only correct orderings of the "words." This, Petkov says, allowed the researchers to determine "how the human and monkey brain evaluate the sequences of sounds from this made-up language."
The brain activity of both species was then scanned with functional magnetic resonance imaging (fMRI) as the participants listened to new sequences of the made-up language. Unlike traditional MRI — which gives us only an image of the brain's anatomy — fMRI allows doctors to look specifically at metabolic changes. That is, it allows us to see patterns or changes in function going on within the brain. The new sequences the participants heard were in either a legitimate order or one that was unexpected and incorrect. The fMRI scans showed that, when they were played the new sequences, a particular region in the brains of both groups — the ventral frontal and opercular cortex — responded to the order that both species had learned to expect.
The results suggest that the function of this frontal region — which in humans is one of the areas involved in processing the order of words — is shared in both humans and primates. The brain scans the organization of what is heard — an important cognitive function that provides a foundation for the more complex language abilities of humans. Perhaps most significantly, the results provide evidence that some of the functions of this brain area are shared by other animals. "Identifying this similarity between the monkey and human brain," says Petkov, "is also key to understanding the brain regions that support language but are not unique to us and can be studied in animal models using state-of-the-art neuroscientific technologies."
According to the National Aphasia Association, the condition currently affects around 1 million people in the U.S. Every year, 180,000 people are newly affected — 80,000 of them as a result of stroke — and it is more common than Parkinson’s disease, cerebral palsy or muscular dystrophy. Building on these developments, the Newcastle team — along with colleagues at the United Kingdom's Cambridge and Reading Universities — have begun a project to study the function of this brain region and its role in language impairment in aphasic patients with stroke. Petkov suggests that their research could be of great benefit with both diagnosis and prognosis for aphasia sufferers. "This will help us answer questions on how we learn language and on what goes wrong when we lose language," he says.