The brain activation of Japanese-English bilingual in sentence comprehension:
An fMRI study

Hideyuki Okamoto*#, Daiko Takahashi**, Yuko Sassa*, Motoaki Sugiura*, Naho Ikuta*, Kazuki Iwata*, Jobu Watanabe*, Yuko Akitski*#, Naoki Miura*##, Katsuhiko Matsue % and Ryuta Kawashima*#

*NICHe, Tohoku University ; **Graduate School of International Cultural Studies, Tohoku University ; #Graduate school of medicine, Tohoku University ; ##Graduate School of Engineering, Tohoku University ; % Kansei Fukushi Research Center , Tohoku Fukushi University

Introduction:

Acquisition of second language is one of the interesting topics for human brain function. In the universal grammar, it is asserted that human language system has generic rules and parameters to construct sentence, and that parameter's value is decided and fixed by mother tongue. In addition, the hypothesis of critical period asserts that the best period to acquire mother tongue is the early time of childhood. In general, when second language has been acquired in early time of childhood, the level of language ability became similar to mother tongue, but if second language has been acquired in adulthood after critical period, language ability became lower levels. However, some of persons who learned second language after critical period (late type bilinguals) have high proficient ability of second language. In this case, it isn't well known whether the parameter's values which is fixed in the language system of late type bilingual are fixed by mother tongue or by second language, or by both languages.

If the idea of universal grammar and the hypothesis of critical period correctly represent the brain function of language in late type bilinguals, it is expected that late type bilingual may comprehend second language using the way different from mother tongue, since the fixed parameter values aren't changeable in adult. Then, it may be observed that brain area(s) responding to process second language is different from brain area(s) to process mother tongue. We investigated brain areas involved in processing mother tongue and second language in Japanese-English bilingual who is learned English during adolescents.

Method:

Ten right-handed volunteers measured their brain activity during an error detection task using functional magnetic resonance imaging (fMRI). All were late type bilingual speaker, who learned English during junior and senior high schools, and who underwent special training of English conversation. All had the experience living in English speaking countries and had high skill of English. In the error detection task, abnormal and normal syntax sentences were prepared both in English and Japanese. Subjects were asked to listen to these four kinds of sentences, and asked to judge whether syntax of the sentences was correct or not by pushing buttons. Brain activation was measured by fMRI using event-related design.

Results:

During hearing normal Japanese sentences, activation was observed in the middle temporal cortices of the bilateral hemispheres. Although, during hearing Japanese sentences with syntax anomaly, activation was observed in the superior temporal cortices of the right hemisphere, as well as the premotor area, the Broca's area and the middle temporal cortices in the left hemisphere. Also, during hearing normal English sentences, areas in the middle temporal cortices of the right hemisphere, and the premotor area and the middle temporal cortices of the left hemisphere, were activated. However, during hearing English sentences with syntax anomaly, activation was observed in the middle temporal cortices of both hemispheres.

Discussion and Conclusion:

The recent studies report that the premotor area and the Broca's area are involved in processing syntax of language. In our result, during hearing abnormal Japanese sentence, premotor area and Broca's area were activated. This result indicates that these areas are sensitive to the syntax anomaly. Otherwise, in our study, premotor area and Broca's area were not activated during hearing abnormal English sentence. This result suggests that the way to recognize anomaly of English syntax in late type bilingual may be different from the way to recognize anomaly of Japanese syntax as mother tongue.