PROJECT SUMMARY/ABSTRACT Language impairment is common in temporal lobe epilepsy (TLE) and often correlated with the amount of pathology in the anterior temporal lobe. Language deficits can also be exacerbated by surgical removal of critical language structures on the language-dominant side. The majority of epilepsy research is with monolingual, native English speakers, which is a problem given the rapidly growing number of bilingual individuals and considerable data showing that language is processed differently in the bilingual vs monolingual brain. Bilinguals are known to 1) perform worse than monolinguals on language measures—in particular on those designed for monolinguals—which suffer from cultural and linguistic biases and 2) show more bilateral language representation. This suggests that current clinical interpretation of a bilingual's presurgical language data may lead to false positives (i.e., classifying a patient as impaired and falsely assuming temporal lobe pathology when language structures are intact) or inaccurate prediction of post-operative language decline. We hypothesize that the clinical utility of pre-surgical language assessment would improve with the use of culturally and linguistically sensitive measures tailored to bilinguals. Studies to date tested bilinguals in only one language and/or used self- reported language proficiency ratings which are known to be less reliable. Further, there is a lack of studies combining neuropsychological data with neuroimaging to evaluate the functional and structural integrity of the temporal lobes in bilinguals. In Aim 1, we evaluate whether a novel, tailored approach that objectively measures language proficiency and naming in both languages is superior to a conventional approach that assesses proficiency only by self-report and tests naming with monolingual-normed measures. The tailored approach would ensure that impairment is defined based on a bilingual's dominant language. In Aim 2, we examine whether language phenotypes will differ as a result of approach using functional MRI and diffusion tensor imaging, and whether bilingual language factors (e.g., proficiency, age of acquisition) influence laterality. Aim 3 determines whether the tailored approach predicts post-operative language decline and if bilingual language factors are related to post-operative outcomes. We leverage a multisite, retrospective and prospective dataset obtained from three large University of California epilepsy centers. Fulfillment of these aims will improve precision medicine and shed light on the combined effects of bilingualism and TLE on language network re-organization, while providing the applicant with training in multimodal imaging and clinical research with a neurosurgical population. This will lead to a K-award and career as a research neuropsychologist trained in imaging, with a special focus on bilingualism, which is often correlated with minority status in the USA.