Language-specific and language-general mechanisms in bilingual aphasic individuals

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PROJECT SUMMARY/ABSTRACT Speaking multiple languages is the norm for the majority of the population of the world. However, research on the neural bases of multilingualism has not been commensurate with the demographic relevance of this population. In no small part, this has been due to the traditionally lower socioeconomic or immigrant status of multilingual individuals. Consequently, there is a lack of fundamental knowledge about the organization and interaction between languages in the bilingual brain. This lack of knowledge has appalling implications for planning behavioral and surgical treatments for bilingual individuals with neurological disorders: it is currently unclear which cortical tissue needs to be spared, and how much and how often each language should be targeted to maximize recovered language function after brain damage in bilingual individuals. Thus, there is a critical need to obtain a better understanding of how multilingual individuals’ languages are organized and how they interact at different levels of representation to inform the development of strategies that maximize potential language recovery after brain damage in a demographic group that will be the majority of the US population by 2040. The proposed project will address this gap in knowledge by combining the study of aphasic and healthy Spanish- English bilingual individuals in behavioral and fMRI tasks to create a symbiosis where theory and praxis mutually inform each other. Specifically, the project will investigate the typology of deficits in post-stroke aphasic bilinguals at the lexical level (i.e., single-word level; Aim 1A), and at the morphosyntactic level (i.e., how words are combined into meaningful phrasal/sentential structures; Aim 1B) through the analysis of a spontaneous speech corpus. The validity of the conclusions derived from these analyses will be tested and confirmed with tailored behavioral experiments (Aim 1C). Aim 2 will target the neural bases of these processes through a combination of voxel-based lesion-symptom mapping in post-stroke aphasic bilinguals (Aim 2A) and fMRI analysis of healthy bilingual individuals (Aim 2B). Critically, by combining the study of a large speech corpus, targeted experimental paradigms, and neuroimaging research, the proposed project holds the potential to obtain a comprehensive characterization of bilingual individuals’ language organization across linguistic levels. This information will constitute the first step to subsequently develop theoretically informed language recovery strategies, and protocols tailored to the needs and characteristics of brain damaged bilingual individuals. Thus, the successful accomplishment of the projects laid out in this proposal will establish the basis to develop strategies that maximize potential language recovery after brain damage in a demographic group that will soon be the majority of the US population. This award will also provide the candidate, who has a strong background in cognitive neuroscience and electrophysiological methods, with critical training in patient testing and neuroimaging methods, to promote a successful transition to an independent research career.