The neural basis of word deafness: a frequency analysis

There are two competing theories regarding the neural basis of word deafness.  Empirically we know that it can occur following unilateral left or bilateral lesions in and around auditory cortex (STG).  The unilateral theory says that the relevant speech perception network is left dominant.  Unilateral lesions cause word deafness by simultaneously disconnecting acoustic input from ascending auditory pathway AND by disconnecting callosal fibers from the intact right hemisphere.  Bilateral lesions do the same but clip the right hemisphere inputs at their source. The bilateral theorysays that the relevant speech perception network is bilateral.  Bilateral lesions disrupt the speech perception network, therefore causing word deafness.  Unilateral cases are anomalies, perhaps reflecting atypically strong left dominant language organization.  Here's an argument in favor of the bilateral account based on probability distributions.  Note that there are several simplifying assumptions here, but I believe these bias things in favor of the unilateral theory.According to the CDC (as of September 6, 2017), 795,000 people in the United States have a stroke every year, 610,000 of which are first time strokes. From these numbers, and assuming a 50/50 chance of having a left or right hemisphere stroke, we can estimate the following in a given year:ยท     Number of people with first-time left hemisphere strokes...
Source: Talking Brains - Category: Neuroscience Authors: Source Type: blogs