"If you have damage to the lower pathway, you have damage to the lexicon and semantics," Wilson said. "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."
The study marks the first time it has been shown that upper and lower tracts play distinct functional roles in language processing, the authors write. Only the upper pathway plays a critical role in syntactic processing.
Wilson collected the data while he was a postdoctoral fellow working with patients with neurodegenerative diseases of varying severity, recruited through the Memory and Aging Center at UCSF. The study included 15 men and 12 women around the age of 66.
Unlike many other studies investigating acquired language disorders, which are called aphasias and usually caused by damage to the brain, Wilson's team had a unique opportunity to study patients with very specific and variable degrees of brain damage.
"Most aphasias are caused by strokes, and most of the strokes that affect language regions probably would affect both pathways," Wilson said. "In contrast, the patients with progressive aphasias who we worked with had very rare and very specific neurodegenerative diseases that selectively target different brain regions, allowing us to tease apart the contributions of the two pathways."
To find out which of the two nerve fiber bundles does what in language processing, the team combined magnetic reso
|Contact: Daniel Stolte|
University of Arizona