What parts of the brain distinguish words from sentences?

In English class, your grade doesn’t differentiate between how large your vocabulary is and how well you write a sentence. But recent research shows that your brain does! This evidence may mean that increasing your vocabulary won’t necessarily influence fluency when learning a new language.

Two parts of the brain, Broca’s area and Wernicke’s area, play a large part in processing language. Broca’s area has been linked to speech comprehension and production, and Wernicke’s area is involved in written language and some speech comprehension. Neuroscientists have long known that these two areas communicate, because there are two pathways of white matter between them. But how and what the pathways do has been unclear until now.

Stephen Wilson, associate professor in the Department of Speech, Language, and Hearing Sciences at the University of Arizona, tested 27 individuals with language impairments due to brain damage. (They’re called aphasias by neurologists.) Wilson compared a combination of MRI brain imaging (to determine which pathway was damaged) with language assessment tasks (to determine what language deficiencies they exhibited). He found that patients could process different linguistic components based on which pathway of white matter between Broca’s area and Wernicke’s was damaged. Damage to one pathway affected vocabulary, and damage to the other pathway affected syntax.

In an interview with the University of Arizona, Wilson says, “If you have damage to the lower pathway, you have damage to the lexicon and semantics. You forget the name of things, you forget the meaning of words. But surprisingly, you’re extremely good at constructing sentences.” About the other pathway, he says, “With damage to the upper pathway, the opposite is true; patients can name things quite well… but when it comes to figuring out the meaning of a complex sentence, they are going to fail.”

There has also been speculation that syntax is a skill that distinguishes humans from other animals who have a basic vocabulary, like monkeys and dogs. However, other evidence of species like songbirds understanding syntax contradicts those theories.

Do you notice that vocabulary and syntax feel different to you?