Table 1.
Overview of studies investigating gray matter changes related to global second language proficiency.
| Author | Sample | Learning environment | Method | Analyses | Main results |
|---|---|---|---|---|---|
| Mechelli et al. (2004) | (A) 25 early and 33 late bilinguals; 25 monolingual controls | Early bilinguals: naturalistic setting Late bilinguals: mixed (class-room setting for some, naturalistic learning for others) | VBM (GMD) | Cross-sectional group comparisons (bilingual vs. monolinguals, whole-brain approach) | l-IPC: bilinguals > monolinguals |
| (B) 22 bilinguals | Unknown | VBM (GMD) | Correlation of VBM-changes with proficiency and AOA in bilinguals (whole-brain approach) | l-IPC: positive correlation with L2-proficiency l-IPC: negative correlation with L2-AOA | |
| Osterhout et al. (2008) | Four students learning Spanish in a university course | Non-naturalistic, classroom setting | VBM (GMD) | Pre–post-comparison in l-IPC (ROI-approach) | l-IPC: increases from pre to post |
| Stein et al. (2012) | 10 exchange students learning German | Naturalistic setting | VBM (GMD) | Correlation of VBM-changes with proficiency-changes (whole-brain approach) | GMD-increase in l-IFG correlates with individual increase in proficiency |
| Martensson et al. (2012) | 14 conscripts in the interpreter academy; 17 monolingual controls | Non-naturalistic setting | Cortical thickness, subcortical gray matter volume | Group comparison (interpreters vs. controls, whole brain approach) of cortical thickness and subcortical gray matter changes (pre–post) Correlation of brain changes with proficiency changes (ROI-approach based on group comparison) | Interpreter (vs. controls) showed higher increase in cortical thickness (pre–post) in l-MFG, l-IFG, l-STG and in bilateral hippocampal volume Proficiency correlated with increase in r hippocampus and l-STG |
| Ressel et al. (2012) | 22 Catalan-Spanish bilinguals; 22 Spanish monolinguals | Naturalistic setting | VBM; volumetric measurement of HG | Group comparison (bilinguals vs. monolinguals, whole-brain brain approach) of VBM values. Group comparison of manually segmented HG volumes | No VBM differences at corrected threshold. Bilinguals had higher HG volumes than monolinguals |
| Klein et al. (2014) | 22 simultaneous bilinguals; 22 early sequential bilinguals; 22 late sequential bilinguals; 22 monolinguals | Naturalistic setting | Cortical thickness | Cross-sectional group comparisons (bilingual vs. monolinguals) | Cortical thickness in l-IFG late bilingual > monolingual and early bilingual > monolingual Cortical thickness in r-IFG in monolingual > late bilingual, monolingual > early bilingual Simultaneous bilingual > late bilingual and early bilingual > late bilingual |
VBM, voxel-based morphometry; GMD, gray matter density; l, left; r, right; IPC, inferior parietal cortex; IFG, inferior frontal gyrus; MFG, middle frontal gyrus; STG, superior temporal gyrus; HG, Heschl’s gyrus; ROI, region of interest.