An fMRI study of bilingual sentence comprehension and workload.

To examine the relation between the cortical substrates that support the comprehension of one's native language and those that support a second language, fMRI measures of cortical activation were taken as native Japanese participants, who had acquired moderate fluency in English, listened to auditory sentences in Japanese and English. In addition, to examine the impact of processing difficulty within a language, sentence difficulty was manipulated by including affirmative (easy) and negative (hard) sentences. The volume of activation was greater for English in most of the cortical regions, suggesting that more cognitive effort was required to process English. Also, a high percentage of the voxels that were activated for the Japanese condition were also activated for the English condition, with as much overlap between Japanese and English as between the processing of affirmative and negative sentences within Japanese. Negative sentences elicited greater activation than affirmative sentences primarily for English, indicating that the structural difficulty of negation has a larger impact on cortical activation if it occurs in the context of the second language, which may serve as another source of difficulty. These results suggest that a shared network of cortical regions supports the processing of both a first and a second language, such that the second language requires more computation and activity from the network.