Differences in neural substrates of comprehension in bilinguals and monolinguals

Introduction With regards to sentence processing in bilingualism, it has been shown that bilinguals activate to a higher extent the left inferior frontal gyrus in syntactic processing when compared to monolinguals. Such differences have been termed as the “neural signature” of bilingualism (Kovelman et al., 2008). However, previous research highlighted the need of distinguishing between grammatical and semantic processes in bilingual sentence comprehension as these two levels have been revealed to differ in the cognitive sub operations that they engage (Wartenburger et al., 2003). The task Forty-three healthy right-handed participants [23 early and high proficient bilinguals in Catalan-Spanish (mean age=23.30) and 20 Spanish monolinguals (mean age=25.10)] were studied. We used a block design including both grammatical and semantic judgement tasks in L1. Sentences were visually presented to both groups. In a grammatical block, sentences were meaningful but could included different types of grammatical violations. For semantic blocks, the sentences were always grammatically correct but could contain semantic violations. The control task consisted of strings of xs of matched lenght.xxx Acquisition and data analyses MR images were collected using a Siemens Avanto 1.5 T scanner (Erlange, Germany). We collected 240 continuous EPI functional volumes (TR = 3000 ms; TE = 50 ms; 35 axial slices). Images analyses were performed using SPM5 software. Preprocessing included realignment, spatial normalization and spatial smoothing (FWHM=8 mm³). In the fixed-effect analysis a full factorial design was set for each subject, modelling each condition separately. The convolution was performed by using the canonical HRF and a t-contrast was defined for each subject as the difference between experimental and control conditions. Results Behavioural analysis showed higher percentage of correct answers for monolinguals than for bilinguals in Control, Semantic and Grammatical conditions. However, differences between groups were not significant (p>0.’05) in any condition. BOLD response was analyzed using one sample t-test for each group (p Bilinguals) did not yield any significant difference. Conclusions Bilinguals activated more brain areas related to language (Wernicke’s area and Broca’s area) that could be considered like a “neural signature” of bilingualism. On the other hand, results neitherdid not show significant differences between semantic and grammatical conditions norneither behavioural differences between groups were found. References Wartenburger I, Heekeren HR, Burchert F, De Bleser R, & Villringer A. (2003). Grammaticality judgments on sentences with and without movement of phrasal constituents- an event-related fMRI study. J Neurolinguistics, 16, 301-314. Kovelman I, Baker SA, & Petitto LA (2008). Bilingual and monolingual brains compared: a functional magnetic resonance imaging investigation of syntactic processing and possible “neural signature” of bilingualism. J Cogn Neurosc, 20, 153-69