Neural basis of language switching using functional imaging in healthy South Indian bilinguals

Abstract

A multifarious network is involved in language processing. The language switching pattern involves synchronised activation & inhibition of different areas of the brain. The aim was to study the neural basis for language code switching in South Indian Kannada-Telugu bilinguals using functional imaging. Cross sectional hospital based study. 20 right handed matriculated late proficient bilinguals(age18-55yrs) were recruited. First(Kannada) language-L1 selection was done using LEAP(Language experience and proficiency questionnaire).Second language(Telugu)-L2 proficiency was evaluated by ISLPR(International Second Language Proficiency Rating Scales).To study the L1 to L2 switch, mixed task and block design fMRI paradigm was used. Subjects were asked to respond to images in Kannada or Telugu. Color cues were displayed with images on screen. fMRI data was acquired with EPI(Echo planner imaging) sequence (no of Dynamics:218, TR-2sec,TE-36sec,3x3x3mm slice thickness)& structural MRI with T1 images in a 3Tesla scanner(Skyra, Siemens).fMRI data was processed in SPM8 software using GLM(Generalised linear model).The group level analysis was done with p<0.05 level of significance with False Discovery Rate(FDR) correction. The areas recruited by the brain during switching from L1(Kannada) to L2(Telugu) were studied. Consistent activation was noted in Caudate, Putamen & right sided frontal gyri along with supramarginal gyrus & rolandic operculum. Language switching is not restricted to a precise area of the brain but is an interface of cortical-subcortical circuitry. The fronto-striatal network governs the language switching. This study can benefit the understanding of involvement & recovery of language domain in various cortical & subcortical diseases.