Left middle temporal deactivation caused by insufficient second language word comprehension by Chinese–Japanese bilinguals

Abstract

Neuroimaging studies of second language (L2) comprehension have reported that the low L2 proficiency of non-proficient learners is associated with greater brain activation in several regions due to the increased deployment of resources to process a not-so-familiar language. However, until now, no attention has been paid to the possibility that the non-proficiency of such learners can actually lead to insufficient use of brain regions where the first language (L1) speakers show increased brain activation. Here, our fMRI study found that the left middle temporal gyrus was less active during the L2 lexical decision of non-proficient Chinese learners of Japanese as L2 than during the L1 lexical decision of native Japanese speakers. Our results indicate that the difficulty experienced by non-proficient L2 learners in L2 lexical decision is due to their less active use of the left middle temporal gyrus, which is, contrastively, used actively by L1 speakers in their L1 lexical decision. These results in turn suggest that left middle temporal activation reflects whether or not the lexical information of L2 words is formed appropriately as part of the L2 mental lexicon.