Neural bases of phonological working memory
Scott, Terri L.
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Phonological working memory (PWM) is the mind's capacity for maintaining and manipulating representations of the sounds important for speech when they are not actively being perceived. It is believed to be a critical component supporting typical language acquisition and vocabulary development, as well as second-language learning. Despite the success of the theoretical framework traditionally used to conceptualize PWM, consensus on its instantiation in the brain remains elusive. In this thesis, I will describe a series of studies designed to interrogate the functionality of the brain regions supporting PWM. In Chapter 1, we compare activation patterns from a canonical PWM task, nonword repetition, to nonword discrimination, a matched task designed to engage core PWM functions, but for the purpose of comparing stimuli, not repeating them. We replicate the findings that PWM during nonword repetition engages speech cortices and show that these cortical regions are also reliably engaged in nonword discrimination, in individual subjects. In Chapter 2, we directly assess the extent to which conjunctive activation between language and working memory paradigms can be interpreted as shared functionality. We find that despite the ability to localize regions in which the majority of subjects show conjunction of significant activation between tasks, the pattern similarity between tasks within those regions vary. We find no pattern similarity between language and spatial working memory, and marginal similarities between language and verbal working memory. Verbal working memory and spatial working memory conjunctions localize a similar network to the multiple demand network and find highly similar patterns of activation in these regions across working memory tasks. Finally, in Chapter 3, we investigate the functional properties of brain areas supporting PWM by comparing activation between nonword repetition, language, verbal working memory, and spatial working memory tasks. We find that PWM shares support with areas involved in spoken language perception, as well as regions engaged by working memory tasks that lie outside of the core language network. Taken together, these studies give a detailed account of the neural bases of PWM, through the lens of shared functionality between this capacity, language, and other domains of working memory.