Bilingualism, Cognition, and Brain Structure
We investigate how the structure of the brain varies with bilingual language experience. We have shown that, relative to monolinguals, heritage language bilingualism is associated with altered cortical thickness asymmetry of the anterior cingulate, an important region for cognitive control, and increased corpus callosum volume in the region connecting right and left cingulate. In a separate sample, variations in cortical thickness of frontal and temporal regions among bilingual children were associated with the extent to which the children were proficient in both of their languages. We also observed that the cortical thickness of the anterior insula predicted speech sound learning among bilinguals, but not monolinguals. These data suggest that variations in bilingual language experience are accompanied by differences in cortical structure. Our lab is continuing to take advantage of the rich bilingual environment of southern California to better understand the neural correlates of specific language experiences, in both young and older adults.
Felton, A., Vazquez, D., Ramos-Nunez, A.I., Greene, M.R., Macbeth, A., Hernandez, A.E., & Chiarello, C. (2017). Bilingualism influences structural indices of interhemispheric organization. Journal of Neurolinguistics, 42, 1-11.
Rodriguez, S., Archila-Suerte, P., Chiarello, C., & Hernandez, A.E. (2018). Anterior insular thickness predicts speech sound learning ability in bilinguals. NeuroImage, 165, 278-284.
Archila-Suerte, P., Woods, E.A., Chiarello, C., & Hernandez, A.E. (2018). Brain morphology of children with balanced and unbalanced bilingualism. Developmental Science. DOI – 10.1111/desc.12654
Individual Differences in Cortical Anatomy
Individual brains differ as much as individual faces do. We explore the nature of individual differences in cortical structure (e.g., cortical thickness and surface area), their relation to language and reading abilities, and the extent of individual variability across various regions of the cortex (see figure below). One particular interest is brain asymmetries in cortical structure. These asymmetries vary depending on handedness strength, and for consistent handers, asymmetry of the insula predicts degree of language lateralization. We have also shown that brain regions with the highest degree of asymmetry are also the most variable in brain structure across individuals. This suggests that reduced biological constraint fosters the expression of strong structural asymmetry.
Chiarello, C., Vazquez, D., Felton, A., & Leonard, C.M. (2013). Structural asymmetry of the insula: Behavioral correlates and individual differences. Brain and Language, 126, 109-122.
McDowell, A., Felton, A., Vazquez, D., & Chiarello, C. (2016). Neurostructural correlates of consistent and weak handedness. Laterality, 21, 348-370.
Chiarello, C., Vazquez, D., Felton, A., & McDowell, A. (2016). Structural asymmetry of the human cerebral cortex: Regional and between-subject variability of surface area, cortical thickness, and local gyrification. Neuropsychologia, 93, 365-379.
Real World Language Use in Multilingual California
The language environment in Southern California is inherently multilingual, and there is a great diversity of language experiences within this population.We use an experience sampling technique with the EAR (electronically activated recorder) to examine bilingual language experience as it is occurring in daily life. Participants wear the EAR for 4 consecutive days as they go about their daily lives. The app is programmed to make 40-second auditory recordings, every 12 minutes during waking hours. Each participant’s speech is transcribed and coded to quantify the frequency of use of various languages, the settings in which the speech occurred, the frequency of language switching, etc. There are two objectives of our initial study: (1) to document the variety and frequency of multilingual language use in the diverse UCR student population; and (2) to assess the correspondence between self-reported language use and actual language use. The initial findings will provide the foundation for a broader research program that will explore the relationship between language experiences and their cognitive and neural correlates.
Cerebral Asymmetries and Right Hemisphere Role in Language
It was long assumed that the left cerebral hemisphere provides the primary neural substrate for language. Using divided visual field techniques, my early research explored the unique contributions of each healthy hemisphere to lexical access, phonological and orthographic processing, and response selection. Our findings demonstrated complementary roles for each hemisphere within each of these language domains, suggesting that language lateralization was not quite as asymmetrical as previously assumed. My lab also made some pioneering discoveries about a unique role for the healthy right hemisphere in the processing of word meaning. In an extensive series of semantic priming investigations, we showed that semantic activation in the right hemisphere is more extensive (less selective) and maintained for a longer period than that subserved by the language-dominant left hemisphere, both in single word recognition and within sentence contexts. We suggested that this broader and sustained meaning activation within the right hemisphere could play a role in figurative language processing, ambiguity resolution, and discourse processing, and these findings led to a re-examination of the importance of the right hemisphere for language processing in context.
Chiarello, C. (1988). Lateralization of lexical processes in the normal brain: A review of visual half-field research. In H.A. Whitaker (Ed.), Contemporary Reviews in Neuropsychology, pp. 36-76. New York: Springer-Verlag.
Chiarello, C., Burgess, C., Richards, L., and Pollock, A. (1990). Semantic and associative priming in the cerebral hemispheres: Some words do, some words don’t, …. sometimes, some places. Brain and Language, 38, 75-104.
Chiarello, C., Liu, S., Shears, C., Quan, N., & Kacinik, N. (2003). Priming of strong semantic relations in the left and right visual fields: A time course investigation. Neuropsychologia, 41, 721-732.
Influence of Reading on Brain Structure and Function
There are marked individual differences in reading skill, even within the population of college students. My lab has investigated language lateralization and potential neurostructural correlates of such variation of reading ability. In particular we have investigated resilient readers, individuals with good reading comprehension despite impaired phonological processing. Our findings indicated that the preserved comprehension was associated with increased dependence on semantic relationships and that resilient reading was accompanied by reduced cortical thickness in temporal-parietal, but not frontal, regions. In a more recent collaborative fMRI investigation, we explored how reading knowledge affects spoken word identification. Identifying auditory words with “neighbors” having different spellings engendered increased activity in cingulo-opercular regions.
Welcome, S.E., Leonard, C.M., and Chiarello, C. (2010). Alternate reading strategies and variable asymmetry of the planum temporale in adult resilient readers. Brain and Language, 113,73-83.
Welcome, S.E., Chiarello, C., Thompson, P.M., & Sowell, E.R. (2011). Reading skill is related to individual differences in brain structure in college students. Human Brain Mapping, 32, 1194-1205.
Chiarello, C., Vaden, K.I. Jr., & Eckert, M.A. (2018). Orthographic influence on spoken word identification: Behavioral and fMRI evidence. Neuropsychologia, 111, 103-111.