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Intracranial mapping of the core spelling and reading networks
Poster Session E, Sunday, September 14, 11:00 am - 12:30 pm, Field House
Oscar Woolnough1, Cale W Morse1, Xavier Scherschligt1, Ellery Wheeler1, Rhea Cho1, Love Zackrisson1, Nitin Tandon1; 1UTHealth Houston
Together, spelling and reading are fundamental aspects of literacy. Both of these are rapid behaviors that engage multiple distributed neural substrates, with core nodes commonly localized to mid-fusiform cortex (mFus), inferior parietal sulcus (IPS), and inferior frontal gyrus (IFG). Functional imaging studies demonstrate a population-level overlap of activation during spelling and reading, however, lesion studies demonstrate behavioral dissociations between spelling and reading, with selective deficits possible in only one of these functions. This implies that, while spelling and reading are closely related behaviors, having been learned together, they are still dissociable within individuals. Here, we use high spatiotemporal recordings to map the neural dynamics that allow us to rapidly spell both known and novel words, and map dissociations between the neural substrates of reading and spelling. We probed this with direct intracranial recordings in 23 epilepsy patients, with extensive electrode coverage across left, language dominant cortex. Participants were auditorily presented with triphonemic CVC real words and novel pseudowords and were asked to spell them aloud, or repeat them aloud after a cued delay. They also read aloud visually presented words and pseudowords. We used this to create a spatiotemporal map of broadband gamma activity (70-150Hz), combined with multivariate models to show how this varied with multiple behaviorally relevant word attributes including lexicality, word frequency, and phoneme-to-grapheme surprisal. We found spelling broadly engaged frontal and parietal cortices, as well as mFus, before activation spread back to early visual cortex. Sensitivity to both word frequency and surprisal while spelling was seen across IFG, IPS and precentral sulcus. Greater activation was seen in these regions, as well as mFus, when spelling known words, while anterior IFG showed greatest activation when spelling pseudowords. Analysis of directed information flow within the core regions of the spelling network indicated that mFus, IPS, and IFG, the primary regions implicated in lesion studies of spelling, act as the most prominent information sources while spelling. We find a partial dissociation between reading and spelling, with temporal and parietal electrodes mostly showing overlap between the two tasks, while frontal electrodes were more likely to show distinct sites selectively engaged by either spelling or reading. We thus isolate the neural spatiotemporal correlates of the core, distributed spelling network involving mFus, IPS, IFG, and precentral sulcus. We provide direct evidence for a dynamic, distributed network underlying this complex behavior, that is modulated by factors that behaviorally influence spelling difficulty. We also demonstrate that reading and spelling do share some cortical resources and are only partially dissociable within individuals.
Topic Areas: Writing and Spelling, Reading