Neural Basis of Simple Arithmetic Processing in a Native and Second Language

Typically, bilinguals learn multiplication facts in their native language (L1), resulting in a performance advantage for arithmetic in L1 compared to a second language (L2). This performance advantage has been shown to be greater for individuals with lower L2 proficiency, suggesting that an individual's language background may play a role in arithmetic processing. The current study aimed to determine whether adult learners of an L2 with limited L2 proficiency engage shared or separate cortical regions to process simple arithmetic across languages. Participants verified small (2 × 3) and large (8 × 9) multiplication problems in both languages, while functional magnetic resonance imaging (fMRI) was acquired. Small problems are thought to engage verbal memory to a greater extent than less practiced, large problems. Participants verified problems faster and more accurately in their L1 than L2. fMRI data suggest that the language differences in performance were not driven by differences in recruitment of the storage of arithmetic facts, as we did not observe expected differences in the engagement of the superior and middle temporal gyri (STG/MTG) across languages. Instead, these adults differentially engaged the left inferior frontal gyrus (IFG) across languages, suggesting that language differences in behavior may have been driven by their ability to engage more effortful arithmetic retrieval processes in L1, but not in L2. Additionally, participants exhibited expected differences in brain activation based on problem size, where small problems engaged STG/MTG and IFG associated with verbal retrieval processes and large problems presented with correct solutions engaged quantity processes associated with parietal regions.