We know that a specific form of magnetic stimulation to the brain can render people unable to speak. But it can get a lot more specific than that. Brain lesions can get so selective, they can knock out a particular form of grammar.
Transcranial magnetic stimulation, or TMS, is both fascinating and terrifying. During TMS, researchers use a machine that creates a magnetic field powerful enough and localized enough to interfere with brain activity. It gives you very temporary brain damage. This interference can be targeted to very specific areas of the brain — as we see in the clip below.
That looks terrifyingly like something that people would be required to wear in a dystopia like the one in Harrison Bergeron. (In that world, the government forced everyone to be equal by putting masks on the beautiful, by distracting the clever, and by weighing down the strong.) Put a wand next to your head, and your fine motor control, or your ability to speak, is just gone. Fortunately, so far we are only using TMS to pin down where different abilities are traditionally housed in the brain.
It's not surprising that the wand can take out the ability to speak, to do math problems, or to move. What's surprising is how specific it can get. The brain is so specific that different areas take charge of different parts of grammar. In one experiment, people were asked to fill in the missing word from a pair of sentences. The sentences were not hard. They were things like, "One child. Many ______." They were also sentences like, "Today I dream. Yesterday, I ________." If you notice, one type of sentence deals with nouns, while the other deals with verbs. Put the TMS wand over the left anterior midfrontal gyrus, and people can still manipulate the nouns. They can't manipulate verbs anymore. There isn't just a section of the brain marked "language." Different parts of the brain deal with different kinds of language.
What exactly does this mean? Some think that there is a pathway in the brain that deals with nouns specifically. It is in charge of identifying and naming things. The motor area of the brain is more concerned with verbs and action words. The difficulty, then, is figuring out where words like, "music" or "meeting" stand. Music is a noun, but it is an intangible one. A meeting is a noun, but it's one that is also a kind of modified verb, in that a meeting is a group of people coming together. Which part of the brain deals with which word?
Discoveries like this are also intriguing in that they imply that the brain itself is responsible for grammar. We might have been sorting words into groups based not just on logical categories, or even fanciful ones, but because different groups of words were literally processed differently in our heads. Grammar might be an expression of neuroscience.