Seeking the neural basis of grammar : English noun and verb morphological processing investigated with rapid event-related fMRI and intracortical electrophysiology

Abstract

(cont.) the functionality of the fMRI data analysis and visualization tools used at Massachusetts General Hospital. I analyze and interpret an 18-subject fMRI experiment I ran using the new task design and software tools. Finally, I present preliminary findings on linguistic questions as well as the nature of fMRI signal, using direct Electrophysiological data recorded from electrodes implanted in the brains of two Epilepsy patients. These patients had electrodes implanted through or near classical language areas of their brains, as a necessary clinical step in locating and surgically removing the seizure-causing tissue. The main findings of this thesis are: 1.) Morphology alone can activate Broca's area, 2.) Other areas are involved, including BA47, anterior insula, and SMA, 3.) Broca's area and BA47 respond to application of abstract grammatical features, even without phonological manipulations, 4.) Morphophonological manipulation additionally recruits insula and SMA, 5.) While simply accessing nouns versus verbs may involve separable brain regions, inflectional processing of the two categories may be done by the same process, 6.) Regularly and Irregularly inflected verbs show a double dissociation of activation in frontal and medial regions, 7.) Processing of English noun more than verb morphology may rely on some contribution from number processing brain systems ...

Inflectional morphology is the component of language concerned with changing a word's form to reflect context-specific meaning, such as the affixing of"-ed" for English verbs in the past tense, or adding "-s" in order to signal a noun's plural form. Although it is but one part of language, morphology may be useful as a model system for larger issues in language and cognition. Morphological processing touches on: the manipulation of memorized items (the vocabulary of words, and maybe word endings), the application and power of combinatorial rules (to generate correct forms, even of unknown words), and the binding of units of information into meaning. Morphology's relationship with other more traditional facets of language such as syntax (sentence structure) and semantics (meanings of individual words) is debated, as is the objective reality of grammatical categories (e.g. noun/verb) as well as combinatorial rules. Functional Magnetic Resonance Imaging (fMRI) is an exciting technique for peering into the brain and answering questions about its function. However, the technique has limited temporal and spatial resolution, and indexes the brain basis of cognition only indirectly, via blood response to cellular metabolism. In this thesis I propose a task for manipulating morphological production, embedded in a 2*2*3 design simultaneously varying grammatical class (nouns versus verbs), regularity of inflection (e.g. words like "walk" which take the stereotyped or regular ending "-ed", versus those like "bring" and "sing" which have idiosyncratic past tense forms), and three types of morphological task aimed to separate the assignment of grammatical features (e.g. present/past tense) from changes in word sound. I introduce and utilize software to extend