<p>Numerous studies in the bilingual literature have shown that cognitive control adapts to several factors related to second language (L2) learning. However, whether third language (L3) learning influences cognitive control remains underexplored. In this longitudinal study, we analyzed behavioral performance and functional magnetic resonance imaging (fMRI) data among Chinese-English bilinguals at resting-state and during a flanker task both prior to English (L2) or Japanese (L3) learning and one year later. During brain resting-states for these same learners, we conducted a correlation analysis between language exam scores and functional connectivity strength of resting-state data after one year of study. The connectivity between the left anterior cingulate cortex (ACC) and the left precuneus was positively correlated with English listening performance, while the connectivity between the right supramarginal gyrus (SMG) and the right inferior parietal lobe (IPL) was negatively correlated with English oral performance. The behavioral results from the flanker task showed that after one year of L2 learning in a classroom setting, a significantly smaller flanker effect emerged among Chinese-English bilinguals. Moreover, brain imaging revealed that incongruent flanker trials elicited greater activation of the left superior frontal gyrus (SFG) than congruent trials. These behavioral and neural patterns were not found among Chinese-English bilinguals who had studied Japanese for one year. Taken together, these findings suggest that cognitive control adapts to L2 learning, but appears to be unaffected by L3 learning.</p>