Today's fact:
You know how I told you that the left side of the brain is usually responsible for language? Well, it's even weirder than that. There's a part of the left hemisphere that is mostly responsible for understanding language, and another part of the left hemisphere that is mostly responsible for producing language using grammar!
Unfortunately, a lot of our evidence for these "language centers" in the brain comes from people with some kind of acquired brain injury (like a stroke or a localized trauma) in those areas. When brain damage causes difficulty speaking or understanding language—but understanding the world and how things work is mostly okey—the patient is diagnosed with aphasia, or impaired language. So someone with aphasia might know how to use a toothbrush, but if you were to ask them about it, either they might not understand you or might not be able to answer you.
If Broca's area is damaged, most people present with impaired expression, and it is harder for them to make grammatical sentences. They are more likely to use "telegraphic" speech, like "Doctor...leg...bad." I am currently reading a paper about how Broca's area deals with complicated pattern recognition that is difficult for most other species. (I'll write about pattern recognition in Broca's later—thanks to a friend who showed me this paper!)
Notice that Broca's area (producing grammatical language) is very close to the motor strip, which controls motor movement. So people who have damage to Broca's area often also have muscular problems and muscle-planning problems too. So basically, talking is hard!
Damage to that other area, Wernicke's, causes problems understanding language. Patients with Wernicke's aphasia may talk a lot, but what they say doesn't make sense. They'll say things like "Isn't that terrible? I know what they're saying. The thing comes in right here and goes out and they say do that and two, and ten, and twenty, and five of them. I don't really do that stuff." The grammar is fine, mostly, but they talk and talk and nobody understands what they're saying. And they don't understand what other people are saying—but if it's really bad, they don't know that they don't understand. (This makes therapy very interesting!)
There are other kinds of damage that can be done. If the arcuate fasciculus (the axons connecting Broca's and Wernicke's areas) is damaged, but nothing else, the patient may be able to understand things pretty well and have pretty good speech (except for some word-finding errors), but they won't be able to repeat things. They will hear what is said, and their Wernicke's area will interpret it for them, but it won't make it to Broca's area to be spoken. Or if there is damage to the areas of the brain surrounding the language areas (but not in the arcuate fasciculus), they may have impaired understanding or expression, but they will be able to repeat things. And if there is damage right at the beginning of the main artery that supplies blood to the left hemisphere's language centers, the patient will probably be diagnosed with global aphasia—understanding, repeating, speaking—everything is impaired.
It's complicated—and remember too that every brain is wired a little differently!
This has been a tour of the language centers of the brain as evidenced by aphasia.
Unfortunately, a lot of our evidence for these "language centers" in the brain comes from people with some kind of acquired brain injury (like a stroke or a localized trauma) in those areas. When brain damage causes difficulty speaking or understanding language—but understanding the world and how things work is mostly okey—the patient is diagnosed with aphasia, or impaired language. So someone with aphasia might know how to use a toothbrush, but if you were to ask them about it, either they might not understand you or might not be able to answer you.
If Broca's area is damaged, most people present with impaired expression, and it is harder for them to make grammatical sentences. They are more likely to use "telegraphic" speech, like "Doctor...leg...bad." I am currently reading a paper about how Broca's area deals with complicated pattern recognition that is difficult for most other species. (I'll write about pattern recognition in Broca's later—thanks to a friend who showed me this paper!)
Notice that Broca's area (producing grammatical language) is very close to the motor strip, which controls motor movement. So people who have damage to Broca's area often also have muscular problems and muscle-planning problems too. So basically, talking is hard!
Damage to that other area, Wernicke's, causes problems understanding language. Patients with Wernicke's aphasia may talk a lot, but what they say doesn't make sense. They'll say things like "Isn't that terrible? I know what they're saying. The thing comes in right here and goes out and they say do that and two, and ten, and twenty, and five of them. I don't really do that stuff." The grammar is fine, mostly, but they talk and talk and nobody understands what they're saying. And they don't understand what other people are saying—but if it's really bad, they don't know that they don't understand. (This makes therapy very interesting!)
There are other kinds of damage that can be done. If the arcuate fasciculus (the axons connecting Broca's and Wernicke's areas) is damaged, but nothing else, the patient may be able to understand things pretty well and have pretty good speech (except for some word-finding errors), but they won't be able to repeat things. They will hear what is said, and their Wernicke's area will interpret it for them, but it won't make it to Broca's area to be spoken. Or if there is damage to the areas of the brain surrounding the language areas (but not in the arcuate fasciculus), they may have impaired understanding or expression, but they will be able to repeat things. And if there is damage right at the beginning of the main artery that supplies blood to the left hemisphere's language centers, the patient will probably be diagnosed with global aphasia—understanding, repeating, speaking—everything is impaired.
It's complicated—and remember too that every brain is wired a little differently!
This has been a tour of the language centers of the brain as evidenced by aphasia.
Brought to you by the letter B!
ReplyDeleteBrain fact that I learned recently: In Michelangelo's "The Creation of Adam" painting, the cloud surrounding God the Father is purposely shaped like a cross-section of the human brain.
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