Neuroscientists have long known that particular areas of the brain are responsible for the comprehension and production of language. But new research points to the criticality of pathways between these areas for various components of language.
From a Science Daily article summarizing the research:
Two brain areas called Broca’s region and Wernicke’s region serve as the main computing hubs underlying language processing, with dense bundles of nerve fibers linking the two, much like fiber optic cables connecting computer servers. But while it was known that Broca’s and Wernicke’s region are connected by upper and a lower white matter pathways, most research had focused on the nerve cells clustered inside the two language-processing regions themselves.
If you have damage to the lower pathway, you have damage to the lexicon and semantics. You forget the name of things, you forget the meaning of words. But surprisingly, you’re extremely good at constructing sentences.
With damage to the upper pathway, the opposite is true; patients name things quite well, they know the words, they can understand them, they can remember them, but when it comes to figuring out the meaning of a complex sentence, they are going to fail.