Title: Neural circuits for reading, inflecting and producing words
Description: This dissertation details brain circuits for language, from visual input (reading) to linguistic output, with unique resolution of anatomy, timing, and physiology. The experimental task used throughout focuses on grammar, the system for constructing phrases from words and word endings. Participants saw words and had to repeat them silently, or silently convert them to past-tense or plural forms. Paper One reports functional magnetic resonance imaging (fMRI) in 18 healthy adults. A main finding was that this task engaged regions of Broca's area (BA), similarly for nouns and verbs, and independently of computing phonology or word sounds. BA has been controversially associated with other aspects of grammar. Also, the other brain regions engaged by the task included Wernicke's area (WA), the visual word form area (VWFA), and early visual cortex (V1/V2). Paper Two focuses on BA and reports direct (intracranial) recordings from populations of brain cells within the region, in patients with electrodes implanted for presurgical evaluation. Four distinct stages of linguistic processing are differentiated that would otherwise overlap in time or space at the resolution afforded by non-invasive methods such as fMRI.

Paper Three extends the spatiotemporal resolution of intracranial recordings to the broader set of regions identified in Paper One. Neuronal activity began first in V1/V2, then in VWFA, and thereafter in WA then BA (mostly overlapping in time). Physiological resolution unique to the method allowed this activity to be categorized further into types more associated with information flow into versus out of the regions, and these followed different time courses. Paper Four reports cell populations that activate in synchrony throughout the identified regions, during an early period when visual areas are first activated and during a later period when BA and WA are most active and the response word is being produced. In the context of the previous papers, these findings suggest that these widelyseparated regions of the brain synchronize temporarily to deliver visual input to the language system, then grammar-specific processing takes place locally within traditional language areas, and finally the regions synchronize again and processed information is combined to generate the linguistic output.