Chapter 15 Cognitive processes underlying reading and writing and their neural substrates

There is a convergence of evidence from studies of lesions (and areas of dysfunctional brain tissue) associated with alexia and agraphia and from functional imaging studies of reading and spelling in normal subjects that these complex processes require a network of interacting brain regions, each with a distinct role in reading and/or writing. For example, Fig. 15.5 shows the areas of activation revealed by fMRI during a task that required knowledge of the spellings of words (adapted from Hsieh and Rapp, 2004). The functional imaging data and evidence from stroke patients together suggest some specialization of neural regions for particular cognitive processes underlying these complex tasks of reading and spelling, and that damage to any one of these regions can disrupt reading and/or spelling, albeit in different ways. Fig. 15.6(A), shows the areas of brain that when damaged (as indicated by DWI and/ or conventional MRI or CT) or hypoperfused (as indicated by PWI or PET) result in impaired reading and spelling as reviewed above. Fig. 15.6(B) shows the areas of activation in response to spelling tasks in normal subjects (data from one representative subject shown). Fig. 15.6(C) shows a meta-analysis of areas of activation in response to reading in normal subjects (adapted from Turkeltaub et al., 2002). Together, these studies indicate that at least the following regions are necessary, and perhaps sufficient, for reading and spelling: left PIFG (BA 44), left dorsal lateral prefrontal gyrus (BA 6), left posterior STG (BA 22), and left inferior temporal/fusiform gyrus (BA 37). Although there is striking convergence of data from various methodologies that these areas comprise a network of neural regions involved in reading and spelling, the precise roles of each of these areas are just beginning to be defined.