Structural And Effective Brain Connectivity Underlying Language Switching In Bilinguals

Bilingual experience or second language(L2)learning is often accompanied by changes in the structure and function of the brain,and structural changes are usually closely related to changes in functions.However,previous studies have not directly explored the relationship between structural connectivity of the brain of second language learners nor effective connectivity under language control tasks,and whether the two will affect the behavioral performance of language control.In this study,75 Chinese native English L2 learners performed picture naming language switching task in magnetic resonance imaging(MRI)scanner.Functional MRI(fMRI)data during task performance as well as high-angle resolution diffusion weighted imaging(HARDI)data were collected.According to the results of the general linear model(GLM)of fMRI data,the left dorsolateral prefrontal cortex(dlPFC),dorsal anterior cingulate cortex and pre-supplementary motor area complex(dACC/pre-SMA)and left caudate nucleus(CN)were selected as regions of interest(ROIs).Then,functional effective connectivity during task performance were estimated,and tractography between the three regions were reconstruct.Finally,the influence of white matter fiber density between ROIs on the effective connectivity were estimated,using parametric empirical Bayesian(PEB)model.Results show that 1.In the language control task,the left dlPFC,left CN,inferior parietal lobe(IPL),precuneus,and dACC/pre-SMA were significantly activated.2.In the language control model with left dlPFC,dACC/pre-SMA and left CN as ROIs,switching or non-switching stimuli first enter dACC/pre-SMA,and then,the information flow enters the left CN through synaptic connection.Here,it forms a bidirectional effective connection with the left dlPFC.3.There is a nonlinear relationship between the effective connectivity during language control and the structural connectivity of the L2 learners' brain.Specifically,the fiber density between dACC/pre-SMA and left dlPFC has a positive influence on the bidirectional effective connectivity between left dlPFC and left CN.Further,effective connectivity between ROIs can predict participants' fiber density between the two abovementioned ROIs.Findings of the present study contribute evidence towards functional effective connectivity during bilingual language control and structural connectivity in the brains of L2 learners,as well as evidence towards non-linear relationships between functional effective connectivity,structural connectivity,and behavioral performance in relation to bilingual language control.