The brain is an exciting and delicious place. There are regions responsible for processing sight, sound, and other sensations, but the brain also houses specific areas that deal with processing and producing language. Mainly, we have two parts which are mostly concerned with language: Broca's Area, which takes care of laying the framework and syntax of grammar, and also helps with speech planning and production; and Wernicke's Area, which is in charge of storing your mental dictionary and comprehending the speech that's flying your way.
We can say this because of a variety of brain imaging techniques that let us see what happens in our skulls when we encounter language, and we talk about two of them. In the first, functional Magnetic Resonance Imaging, or fMRI, we present some language stimulus, like some sounds or words or a sentence, and then spin up the magnet and get a picture of where in the brain was just active doing the processing. This is great at telling us where language is, but isn't great at telling us when the different bits of processing happen, since you're measuring after the fact. Electroencephalograms, or EEGs, do better at this: they take non-stop measurement through an electrode cap on the skull of all activity happening in the brain over time. So they can tell us what order things happen in, and how long it takes to process language. But even with a lot of electrodes spread out over the head, they're not really great at telling us exactly where the processing is happening in the brain. Can't get everything!
We did talk in the video about two neurolinguistic techniques, EEG and fMRI, but we didn’t talk about all the testing paradigms, and so here, we'll introduce one more, and one that's different in an important way from the other methods of looking at the brain we have.
So the thing about EEG and fMRI and the other testing techniques is that they’re all correlative - we see particular changes go along with particular stimuli, and then we say those changes are the result of the stimuli, because we don’t see them when the brain hears or sees other kinds of words or sentences. Our findings are quite robust for a lot of the basics of language processing, but it’d be cool if we could have causation, too, right? Causation is the gold standard of science research, if we can get it.
One way to do this is to look at aphasia, and see where the brain damage occurred, and link that injury to language ability. But the thing is, strokes or brain tumors or trauma aren’t usually specific - it’s not just the language area or some part of it that gets damaged, but more of the surrounding brain tissue, too. Which is unfortunate for both the patient and for the researcher who wants to pin down what the problem is, and help the patient out!
So what can we do? Well, that’s where repeated transcranial magnetic stimulation, or rTMS, comes in. In rTMS, you get an electric coil placed up against your head, and then repeatedly stimulate with the coil a given spot in the brain, over and over again, for a while. It’s not exactly pleasant - it feels like getting flicked with a rubber band on the scalp every few seconds for several minutes, or more, depending on what kind of test you're running.
But this is useful because rTMS can actually block activity in a specific region of the brain for a short period of time. That’s right! Artificial lesions in your brain. Cool and scary all at once, this one. But it’s super great for causation! Now you can see that your brain is doing some task just fine; then block a given brain section for a bit, and see that you can’t do that same task you just were so great at anymore; and then let your poor head recover and find, suddenly, you can do it again! So we can back up some of our other theories.
The other cool thing about rTMS is its ability to really target very narrow regions in the brain. That means we can see, for example, that processing verbs and nouns doesn’t happen in the exact same place. (The full paper is here.) In this experiment, people had one small region in the brain, the left anterior midfrontal gyrus, taken out for a bit by the TMS coil. That’s an important region; it’s basically where Broca’s area is.
These participants were asked to conjugate regular and irregular verbs and nouns. When they were hit in Broca’s area, the ability to conjugate both regular and irregular verbs fell off, but their ability to keep nouns in place stayed the same! And they made sure this was a real effect, too. The researchers also applied TMS to the same area in the right hemisphere, which isn’t helpful for language, and used fake stimulation, so the participants’ brains functioned normally, even if they thought they were have brain service knocked out. But none of that had any effect on their verbal abilities! It’s only with rTMS in Broca’s area that the verb conjugations were impaired.
Super cool, right? We can block out the conjugation ability, but it’s only influencing verbs, not nouns. So where do the nouns go? We have more places to look for here, for sure, but it’s really cool to see the brain in action so directly, without having to go inside the skull or injure anyone.
Brains, man. Just brains.
So how about it? What do you all think? Let us know below, and we’ll be happy to talk with you about the brain and language: where it is, what it's like for perception and processing, and how we can know. There’s a lot of interesting stuff to say, and we want to hear what interests you!