Introduction to language representation in the brain

In this video, I’m going to explain some general terms crucial in neurolinguistics, and we will have a look at language representation in the brain. Language impairments after brain damage can tell us a lot about where language areas are. They are mainly situated in the left hemisphere of the human brain. But individual differences need to be expected in how and where language is stored. Let us look at how language is built. It consists of different levels. Sentences that can be broken down to words that, again, consists of sounds. When a speaker and a listener want to communicate, they use full sentences, such as, a smart woman reads the newspaper at the table every morning.

So here we see nouns, a verb, an adjective, and some smaller units, such as articles and prepositions. Each of those words consists of sounds. We use language for speaking and understanding spoken language, but also for reading and writing. In the case of reading and writing, we use letters or characters. All levels, sentences, words, and sounds and their use, speaking, understanding, reading, and writing, can be independently impaired by brain damage, and those impairments depend on the site of the damage. In the following clips, we will see patients with different locations of brain damage resulting in different language impairments. Broca’s area in the interior frontal gyrus in the left hemisphere seems to be involved in speech production.

It’s named after Paul Broca, who discovered it in the 19th century. Although grammar is not hosted by Broca’s area, we know that damage to this area and its vicinity often results in grammatical disorders. - And nothing that you started back at work for a few hours a week, haven’t you? - Waitress, - Shelf. - Stacking. - Shelf stacking. Very exciting. - But it’s good, just talking and–

Yeah, so it’s good to speak. - And they’ve given you a badge, haven’t they? What does the badge say? - It says stroke and speech problems. And it’s tiny. - Helps people to understand. This patient is struggling with building sentences. She has difficulties using grammar. She may have damage to the frontal parts of the brain, in or near Broca’s area. Wernicke’s area is where the words are stored, where you see a picture like this, the word tree pops up. This happens in Wernicke’s area. Damage to Wernicke’s area will result in word finding difficulties or in using the wrong words. - Hi Byron. How are you? - I’m happy. Are you pretty? You look good. - What are you doing today?

We stayed with the water over here at the moment and talked with the people, put them over there. They’re diving for them at the moment. but they’ll save in the moment here water very soon, for him. With luck for him. - So we’re on a cruise and we’re about to get to Juneau. - We’ll sort right here and they’ll save their hands right there for them. This patient can build correct sentences but has problems choosing the correct words. Notice that all the words he uses are real words, but not the right ones. After a word has been retrieved in Wernicke’s area, it is transported to Broca’s area via the arcuate fasciculus. In Broca’s area, the articulation is programmed.

If you find damage to this tract, the sound structure of words is disrupted. The correct word, tree, is retrieved, but it may be produced as kree. This woman has probably chosen the correct words, but we cannot be sure, of course. But she cannot choose the correct sounds to belong to these words. This makes her speech incomprehensible, because she produces nonexisting words. This woman does not suffer from brain damage, by the way, she probably had a migraine attack. - Well a very very, heavy virtation tonight. We had a very, derrison, by let’s go ahead terrace tase in goes for the bit, they have the pit.

We showed how brain injury can affect language in different ways depending on the site and the size of the damage. So now we have seen that language representation in the brain can be studied by examining language impairments. Notice that we cannot point out the location where grammar or sentence building is hosted. The reason for that is that we need to assume a complex network of areas responsible for doing this. And it is still unknown how this works in detail. Similarly how reading and writing is carried out is not entirely clear yet, but we do know that the angular gyrus plays a crucial role. What we know is that there are individual differences in how language is stored in the brain.

Every brain is unique. Considering this and what we covered so far, the complex levels of language and the impairments to all those levels, you can now understand how important it is to locate these areas very carefully in the individual brain when there is a tumour that needs to be removed, and the only way to do so is by language testing during awake brain surgery.