Arithmetic memory networks established in childhood are changed by experience in adulthood.

Adult bilinguals show stronger access to multiplication tables when using the language in which they learned arithmetic during childhood (LA+) than the other language (LA-), implying language-specific encoding of math facts. However, most bilinguals use LA+ throughout their life, confounding the impact of encoding and use. We tested if using arithmetic facts in LA- could reduce this LA- disadvantage. We measured event related brain potentials while bilingual teachers judged the correctness of multiplication problems in each of their languages. Critically, each teacher taught arithmetic in either LA+ or LA-. Earlier N400 peak latency was observed in both groups for the teaching than non-teaching language, showing more efficient access to these facts with use. LA+ teachers maintained an LA+ advantage, while LA- teachers showed equivalent N400 congruency effects (for incorrect versus correct solutions) in both languages. LA- teachers also showed a late positive component that may reflect conflict monitoring between their LA+ and a strong LA-. Thus, the LA- disadvantage for exact arithmetic established in early bilingual education can be mitigated by later use of LA-.