The Functional Overlap of Executive Control and Language Processing in Bilinguals

Abstract

The need to control multiple languages is thought to require domain-general executive control (EC) in bilinguals such that the EC and language systems become interdependent. However, there has been no systematic investigation into how and where EC and language processes overlap in the bilingual brain. If the concurrent recruitment of EC during bilingual language processing is domain-general and extends to non-linguistic EC, we hypothesize that regions commonly involvement in language processing, linguistic EC, and non-linguistic EC may be selectively altered in bilinguals compared to monolinguals. A conjunction of functional magnetic resonance imaging (fMRI) data from a flanker task with linguistic and nonlinguistic distractors and a semantic categorization task showed functional overlap in the left inferior frontal gyrus (LIFG) in bilinguals, whereas no overlap occurred in monolinguals. This research therefore identifies a neural locus of functional overlap of language and EC in the bilingual brain.

Keywords: bilingualism; executive control; fMRI; language processing.

Figure 1

Example stimuli for the a) flanker and b) semantic categorization task.

Figure 2

Example trial timing for the a) flanker and b) semantic categorization task. Duration of each stimulus is indicated on the right.

Figure 3

a) Behavioral distractor effect magnitudes in each group (collapsed over language for bilinguals) comparing linguistic and non-linguistic distractors (collapsed over congruent, incongruent, and semantic distractor) to control. Error bars show standard error.

Figure 4

a) Results of the flanker task interaction of group * distractor type, crosshairs at [46 –60 0], showing the cluster in the right middle/inferior temporal gyrus. b) Results of the semantic categorization task interaction of group * stimulus type, crosshairs at [−4 −62 −4], with the four clusters labeled.

Figure 5

Overlaid conjunction of the linguistic > control, non-linguistic > control, and word > non-word contrasts, voxel-level corrected at FDR p < 0.05, for a) monolinguals and b) bilinguals (collapsed over language). Axial slices are shown from z = −25 to z = 70. In neurological convention, the left hemisphere is presented on the left.

Figure 6

a) Focus on the LIFG in the bilingual conjunction (using an ROI mask of 10 mm around the statistical peak at −34, 22, −10), at z = −10. Regions of overlap between the linguistic EC, non-linguistic EC, and language processing tasks (collapsed over languages) are indicated by blended colors. b) Conjunction of all three contrasts (collapsed over languages) for bilinguals, at z = −10, showing signal change in the LIFG.