How the Brain Parses Language

Summary

Quanta spoke to Fedorenko about how the language network is like the digestive system, what she knows about how the language decoder works, and whether she really believes that people have LLMs inside their heads. The conversation has been condensed and edited for clarity. What is the language network? There’s a core set of areas in adult brains that acts as an interconnected system for computing linguistic structure. They store the mappings between words and meanings, and rules for how to put words together. When you learn a language, that’s what you learn: You learn these mappings and the rules. And that allows us to use this “code” in incredibly flexible ways. You can convert between a thought and a word sequence in any language that you know. Three brain models in Fedorenko’s office highlight the language network. From top: in purple, embroidery by Laura Bundesen; in red, cross-stitch by Hannah Small; in red, 3D-printed model. Katherine Taylor for Quanta Magazine That sounds very abstract. But you call the language network a “natural kind” — does that mean it’s something physical you can point to, like the digestive system? That’s exactly right. These systems that people have discovered [in the brain], including the language network and some parts of the visual system, are like organs. For example, the fusiform face area is a natural kind: It’s meaningfully definable as a unit. In the language network, there are basically three areas in the frontal cortex in most people. All three of them are on the side of the left frontal lobe. There’s also a couple of areas that fall along the side of the middle temporal gyrus, this big hunk of meat that goes along the whole temporal lobe. Those are the core areas. You can see the unity in a few different ways. For example, if you put people in an [fMRI, or functional magnetic resonance imaging], scanner, you can look at responses to language versus some control condition. Those regions always go together. We’ve now scanned a...