Semantic and attentional networks in bilingual processing: fMRI connectivity signatures of translation directionality

Abstract

Comparisons between backward and forward translation (BT, FT) have long illuminated the organization of bilingual memory, with neuroscientific evidence indicating that FT would involve greater linguistic and attentional demands. However, no study has directly assessed the functional interaction between relevant mechanisms. Against this background, we conducted the first fMRI investigation of functional connectivity (FC) differences between BT and FT. In addition to yielding lower behavioral outcomes, FT was characterized by increased FC between a core semantic hub (the left anterior temporal lobe, ATL) and key nodes of attentional and vigilance networks (left inferior frontal, left orbitofrontal, and bilateral parietal clusters). Instead, distinct FC patterns for BT emerged only between the left ATL and the right thalamus, a region implicated in automatic relaying of sensory information to cortical regions. Therefore, FT seems to involve enhanced coupling between semantic and attentional mechanisms, suggesting that asymmetries in cross-language processing reflect dynamic interactions between linguistic and domain-general systems.

Keywords: Attentional networks; Bilingualism; Functional connectivity; Semantic networks; Translation; fMRI.

Fig. 1.

Task design. The experiment included four conditions: first-language reading (L1R), second-language reading (L2R), backward translation (BT), and forward translation (FT). Each condition comprised 24 sentences, presented in blocks of four pseudo-randomly chosen trials. Each block started with a task-instruction slide lasting 18 s. Trials in the reading and translation conditions were shown for 8 and 15 s, respectively. MRI scanner figure by Peggy.poon.ths [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)], from Wikimedia Commons.

Fig. 2.

Connectivity differences between translation directions. (A) Comparison between FT and BT, relative to their respective baseline reading conditions showed that the ATL was functionally connected with the left IFG, the orbitofrontal cortex and the parietal lobes, including the left superior parietal lobule, the left cuneus, and the bilateral precuneus. (B) Comparison between BT and FT, relative to their respective baseline reading conditions, revealed increased connectivity between the ATL and the right thalamus. L1R: first-language reading; L2R: second-language reading; BT: backward translation; FT: forward translation. L: left; R: right; ATL: anterior temporal lobe; IFG: inferior frontal gyrus; OFC: orbitofrontal cortex; Prec: precuneus; SPL: superior parietal lobule; Thal: thalamus.