Humans have an amazing facility in switching attention between two or more ongoing tasks. This kind of cognitive flexibility allows for successful navigation of the demands of everyday life, but it declines with aging. Recent results have shown that such age-related declines are not as severe in lifelong bilinguals; speaking more than one language on a regular basis since childhood seems to provide some protection from this general effect. Current cognitive models suggest that the basis of this boost relates to the fact that bilinguals are constantly switching between multiple languages, which serves to strengthen task switching and related executive control processes. With support from the National Science Foundation, Dr. Brian Gold and his colleagues at the University of Kentucky will conduct experiments designed to gain a more comprehensive understanding of the cognitive and neurobiological bases of bilingual advantages in executive control processes. The methods used will include standard behavioral experiments and neuroimaging studies conducted with monolingual and bilingual participants. In behavioral studies, participants will engage in task switching and working memory paradigms and reaction time and accuracy data will be recorded. Results will explore whether bilingualism strengthens just those processes that directly replicate the bilingual experience, or if it serves to bolster other executive control processes, such as memory updating. The neuroimaging studies will use functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) methods to understand the neurobiological bases of bilingual performance advantages. The fMRI experiment will identify variations in bilingual brain activation patterns that correlate with their advantages on executive control tasks. The DTI measures will identify variations in white matter microstructure in bilinguals, ones that correlate with the advantages on executive control tasks. The experiments will provide a more precise understanding of the cognitive and neurobiological variables that seem to be protected by lifelong bilingualism.
Results from the present project will be relevant to the question of how accessible lifestyle variables can influence neuroplasticity and/or compensatory brain reserve in aging. It will also provide research training and mentoring to a postdoctoral fellow and two undergraduate research assistants. Trainees will acquire knowledge in neuroanatomy, and the analysis of neuroimaging data. This project will provide information about the relationship between second language learning and neurobiology, an issue of fundamental relevance in our increasingly multilingual society.
Humans have an amazing facility in switching attention between two or more ongoing tasks. This kind of cognitive flexibility allows for successful navigation of the demands of everyday life, but it declines with aging. Recent results suggest that such age-related declines may not be as severe in lifelong bilinguals; speaking more than one language on a regular basis since childhood may provide some protection from this general effect. In this NSF funded research, we conducted functional magnetic resonance imaging (fMRI) experiments designed to understand of the neural bases of bilingual advantages in executive control processes. In the main experiment, the accuracy, speed and brain activation patterns during switching were compared between four participant groups consisting of: 20 young adult monolinguals, 20 young adult bilinguals, 20 senior monolinguals and 20 senior bilinguals. Groups were carefully matched for sex distribution, education level, and several relevant cognitive test scores. The behavioral data showed that all groups were able to switch between two tasks with high accuracy but required different processing times to do so. As expected, seniors showed longer processing times compared to young adults. However, senior bilinguals switched faster than senior monolinguals. In contrast, young adult bilinguals did not switch faster than young adult monolinguals. The fMRI data showed that subjects used a network of brain regions to switch between tasks, most prominently involving frontal regions on both sides of the brain. In addition, the strength of activation of these frontal regions varied depending upon processing speed. Specifically, in each of the four groups, the slowest responders required the strongest activation of frontal brain regions for accurate switching, linking response in these regions with effortful processing. Compared to young adults, seniors showed greater activation in frontal regions linked with effortful processing. However, bilingual seniors showed significantly less activation than their monolingual peers in several of these regions, particularly on the left side of the brain. Thus, senior bilinguals outperform their monolingual peers despite showing less response in frontal regions linked with effortful processing. Together, these data suggest that lifelong bilingualism reduces age-related slowing of task switching by rendering this process less effortful and more automatic. The increased automaticity of switching in senior bilinguals appears to be based on the maintenance of functional efficiency of left frontal regions in aging. At the broadest level, our findings provide further support for a view that positive lifestyle variables can delay cognitive declines in aging. Establishing neural bases of advantages associated with the regular use of two languages should help further promote bilingualism in the United States.
