THE NEURAL SUBSTRATES UNDERLYING BOTH SPELLING AND READING
Purcell, Jeremy Joseph
Written language forms a cornerstone of human communication and understanding. In order to understand why written language can be used skillfully by some and not by others, it is important to investigate the neural basis of how written words are represented in the brain by way of reading as well as writing. Surprisingly, as compared to reading, little work has been done to examine the neural basis of writing and how orthography in general is represented in the brain. This has motivated the three projects discussed here. In the first chapter, I present a quantitative review of studies involving written production. Specifically, I discuss brain regions associated with "central" spelling processes as well as more peripheral writing processes responsible for generating the motor actions needed for producing written words. In the second chapter, I discuss the first functional magnetic resonance imaging (fMRI) study to examine spelling via keyboard typing and then determine if there is overlapping activation across brain regions associated with "central" spelling processes and that of reading. The results of this work demonstrate that a portion of both the left inferior frontal gyrus and ventral occipitotemporal (VOT) cortex are commonly active within the same group of subjects across both reading and spelling. This overlap occurred within a portion of the left mid-fusiform gyrus that is canonically associated with reading and has been termed the Visual Word Form Area (VWFA). Although such work suggests that reading and spelling activate the same regions, it was not clear whether the same neuronal populations within these regions used to read a word were also called upon to spell that same word. Therefore, in the third chapter I present a combined spelling and reading fMRI-Adaptation experiment which tested and confirmed the hypothesis that some of the same neurons within the left IFG and VWFA used to spell a word are also used to read that same word, and that this effect is driven by orthographic (not phonological or semantic) processes. In general this work adds to the literature of written language production and provides a deeper insight into how the brain represents orthography.
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