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Several lines of evidence suggest the importance of phonological working memory (PWM) in language acquisition. We investigated the neural correlates of PWM in young adults who were under compelling social pressure to be bilingual. Equal bilinguals had high proficiency in English and Chinese as measured by a standardized examination, whereas unequal bilinguals were proficient in English but not Chinese. Both groups were matched on several measures of nonverbal intelligence and working memory. Inscanner behavioral results did not show between-group differences. Of the regions showing load-dependent increments in activation, the left insula showed greater activation in equal bilinguals. Unequal bilinguals showed greater task-related deactivation in the anterior medial frontal region and greater anterior cingulate activation. Although unequal bilinguals kept apace with equal bilinguals in the simple PWM task, the differential cortical activations suggest that more optimal engagement of PWM in the latter may correlate with better second-language attainment.phonological working memory ͉ functional MRI ͉ intergroup differences I n an increasingly global world, facility with two or more languages is a capability that confers competitive advantages. Of specific interest to the current investigation is why, despite being immersed in the same environment, some individuals have difficulty acquiring a second language even though they have an excellent command of their first language.§ Prior neuroimaging studies have characterized the effects of age of acquisition (1, 2) and amount of linguistic experience in bilinguals (3) on brain activation but, to our knowledge, none have examined functional anatomy underlying differences in second-language acquisition ability.Several lines of evidence suggest that phonological working memory ¶ (PWM) plays a crucial role in determining language acquisition ability (4). It has been proposed that the phonological loop, consisting of a short-term phonological store and a subvocal rehearsal system, exists to facilitate language acquisition (5, 6). Specifically, the phonological loop is thought to temporarily store unfamiliar sound patterns, whereas more permanent representations are being constructed for long-term memory storage (4).In support of these postulates, a number of behavioral studies have shown that measures of PWM, such as digit span and word and nonword repetition, predict the outcome of native language acquisition in children (6 -8) and foreign language acquisition in both children (9) and adults (10, 11). It has also been observed that polyglots have a larger PWM capacity than nonpolyglots (12). Further, neuropsychological studies of patients with defective short-term memory (13) and children with specific language impairment and low achievement (14, 15) provide additional support for the hypothesis that the PWM plays a crucial role in language acquisition. Taken together, these findings point to a compelling link between PWM and language acquisition and suggest that PWM is imp...

The effect of word repetition within and across languages was studied in English-Chinese bilinguals who read rapidly presented word pairs in a block design and an event-related fMRI study. Relatively less increase in MR signal was observed when the second word in a pair was identical in meaning to the first. This occurred in the English-only and mixed-languages conditions. Repetition-induced reductions in BOLD signal change were found in the left lateral prefrontal and lateral temporal regions in both types of conditions in the block experiment, suggesting that processing in these regions is sensitive to semantic features present in words and characters, and that part of the semantic neuronal networks serving English and Chinese is shared. In addition, these regions showed greater absolute signal change in the mixed-languages trials relative to the English-only trials. These findings were mostly replicated in an event-related experiment. Together, the experiments suggest that while the networks for Chinese and English word processing have shared components, there are also components that may be language specific.

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