By Michael Merschel, American Heart Association News
You might not put a lot of thought into what it takes to speak, but speaking keeps your brain busy. In every conversation, multiple regions activate to process sounds, give words meaning and control the muscles that move your mouth.
If someone knows more than one language, the process has even more layers – as do the challenges when such a person has a stroke that limits their ability to speak.
Difficulty speaking clearly or understanding language is called aphasia. Its most common cause is stroke, but aphasia also can result from brain injuries or other diseases. And it can be “devastating,” said Dr. Mira Goral, a professor of speech-language-hearing sciences at Lehman College and the Graduate Center of the City University of New York.
An estimated 2 million people in the U.S. live with aphasia, commonly as a result of stroke, according to the American Stroke Association. It’s not clear how many people have what is often called bilingual or multilingual aphasia. But in the U.S. alone, about 20% of the population speaks a language besides English at home, according to the Census Bureau.
And the numbers affected are likely to grow, said Dr. Swathi Kiran, founding director of the Center for Brain Recovery at Boston University. She noted that the U.S. Hispanic population has been projected to reach 71 million by 2030, and the largest increase in stroke prevalence is expected to be among Hispanic males.
The condition, however, doesn’t know borders. “Most of the world is either bilingual or multilingual,” Kiran said.
Language is just one form of communication, Goral said. It involves vocabulary, grammar, the sound of a spoken word or the form of the written one. It requires understanding of tone and context. And there is no single spot in the brain that handles all those functions. “Each of these linguistic aspects are associated with particular networks in the brain,” Goral said, and “many, many layers” combine to form “this amazing thing” that we use to communicate.
In a multilingual person, things get even more interesting.
Brain regions at work
If a brain is like a computer, Kiran said, a language is like software. And multiple languages are like different programs that run on the same equipment. “It’s not that when you’re learning one language, a certain part of your brain is involved, and when you speak another language, a different part of your brain is involved. It’s actually the same structure.”
A stroke affects everyone differently, Goral said, but patterns emerge.
The most common type of stroke is an ischemic stroke, when a vessel supplying blood to the brain is obstructed. And the most common place for that kind of stroke is in the left middle cerebral artery, which supplies blood to parts of the brain involved in speech and language. (In most people, most language is processed in the left half of the brain.)
The exact effect of a stroke depends on which part of the brain is damaged.
“If there’s a reduction in the blood flow in the main artery, then a person has something called global aphasia,” Kiran said. Many regions of the brain will be affected, and the person will have trouble speaking, understanding, reading and communicating.
Depending on which branch of the artery is blocked, the damage may not be that extensive. If the branch affecting the frontal lobe is affected, the person will have trouble speaking fluently but will understand what’s being said to them, Kiran said. But if another artery is affected, people may be able to speak fluently but have trouble understanding what’s being said.
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