Let’s back up: Despite the fact that the hemispheres of the brain do a lot of work in concert with each other, there absolutely is a general tendency for language to lateralize left, and the details of this tendency are very interesting. The history of neurolinguistics explains a lot about these basic facts, starting with Paul Broca, a French surgeon from the 1800s, who noticed language problems in patients who had experienced trauma to the front left portion of the head, near the temple. This area of the brain is now known as “Broca’s area.”
Around ten years later, a German neurologist named Carl Wernicke noticed that his language-impaired patients had lesions in the left temporal area, which is the same left hemisphere but farther back. (Back then, the discovery could only occur during autopsies, of course.) This part of the left hemisphere, like a neighbor to Broca’s area, is now known as “Wernicke’s area.” (2)
What Is Aphasia?
Aphasia is any disease- or trauma-induced brain damage that causes a language disorder. Though most commonly caused by stroke, it can also be caused by infection, tumors, hemorrhaging, and blows to the head. The worst type is called “global aphasia,” which causes the patient to be mute. (4)
Less severe types of aphasia, when some language is retained, are commonly split into two types called “fluent aphasia” and “non-fluent aphasia.”
Fluent aphasics speak fluidly, as the name implies, but they may not make sense when they speak.
Non-fluent aphasics produce labored speech, and have difficulty structuring their sentences, but their messages are more understandable. (We’ll see some examples of these utterance types shortly.) In addition, the labored speech in the non-fluent type is usually “agrammatic,” which means it lacks functional elements of language such as prepositions, articles, and pronouns. Function words are also called closed-class words, because the closed classes don’t gain new members very quickly. So, people with non-fluent aphasia often form sentences without prepositions, articles, and pronouns, and struggle to get the utterances out. However, they have an easier time with content words like nouns, verbs and adjectives. Content words are also called open-class words, because they gain new members all the time! For a review of this fun language distinction, read Part II of the series “Why Do People Say ‘A-Whole-Nother’?
When people develop language disorders, it is devastating to them and to their loved ones. However, from a scientific perspective, the process of attempting to understand the disorders, and develop treatments, has provided us with vast amounts of information about how language works in a general sense. For example, we know that this linguistic distinction between function words and content words is not just something that linguists made up or imagined. Why? Because much of the non-fluent aphasia—the one that causes agrammatic speech—is classified as “Broca’s aphasia” because it is caused by damage to Broca’s area.
Here is an example of an utterance produced by a Broca’s sufferer, documented by linguist Victoria Fromkin. It was in response to the patient being asked if he had been going home on weekends:
Why, yes…. Thursday uh… uh… uh… no… Friday… Bar…ba…ra…wife… and oh car… drive… you know… rest… and TV.