Denise Klein

Left putaminal activation when speaking a second language : evidence from PET

The neural representation of the languages of the polyglot speaker has been highly controversial. We used positron emission tomography (PET) to investigate whether production in a second language (L2) involves the same neural substrates as that of a first language (L1) in normal bilingual subjects who learned L2 after the age of 5 years. Comparison of cerebral blood flow (CBF) when repeating words in L2 and repeating words in L1 yielded only a single significant CBF change: an increase in the left putamen. We hypothesize that this region plays a specific role for articulation in L2. The role of the putamen in articulation is supported by foreign accent syndrome (FAS), which can occur after left putaminal damage. The increased articulatory demands imposed by speaking a second language may require complex motor control for speech production in L2.

A Cross-Linguistic PET Study of Tone Perception in Mandarin Chinese and English Speakers

PET was used in a cross-linguistic study to determine whether neural mechanisms subserving pitch perception differ as a function of linguistic relevance. We compared tone perception in 12 native Mandarin speakers, who use tonal patterns to distinguish lexical meaning, with that of 12 native speakers of a nontone language, English. Subjects were scanned under two conditions: a silent resting baseline and a tonal task involving discrimination of pitch patterns in Mandarin words. Both groups showed common regions of CBF increase, but only Mandarin speakers showed additional activation in frontal, parietal, and parieto-occipital regions of the left hemisphere; this latter finding indicates that language experience may influence brain circuitry in the processing of auditory cues. In contrast, only the English group showed activity in the right inferior frontal cortex, consistent with a right-hemispheric role in pitch perception.

Cerebral organization in bilinguals: a PET study of Chinese-English verb generation.

Positron emission tomography (PET) was used to investigate cerebral organization in seven subjects who had Mandarin Chinese as their native language (L1), and learned English (L2) later in life. When activation from word repetition was subtracted from verb generation in L1 and L2, CBF increases were observed for both languages in left inferior frontal, dorsolateral frontal, temporal and parietal cortices, and right cerebellum. Direct comparison of the difference between verb generation and word repetition in L1 and L2 revealed no significant differences. Within-subject analysis of verb generation minus word repetition yielded CBF increases in left frontal cortex for all individuals for L1 and L2, and a comparison of differences yielded no spatial separation in frontal peaks. We argue for shared neural substrates even for such contrasting languages as Mandarin and English.

Age of language learning shapes brain structure: a cortical thickness study of bilingual and monolingual individuals.

We examined the effects of learning a second language (L2) on brain structure. Cortical thickness was measured in the MRI datasets of 22 monolinguals and 66 bilinguals. Some bilingual subjects had learned both languages simultaneously (0-3 years) while some had learned their L2 after achieving proficiency in their first language during either early (4-7 years) or late childhood (8-13 years). Later acquisition of L2 was associated with significantly thicker cortex in the left inferior frontal gyrus (IFG) and thinner cortex in the right IFG. These effects were seen in the group comparisons of monolinguals, simultaneous bilinguals and early and late bilinguals. Within the bilingual group, significant correlations between age of acquisition of L2 and cortical thickness were seen in the same regions: cortical thickness correlated with age of acquisition positively in the left IFG and negatively in the right IFG. Interestingly, the monolinguals and simultaneous bilinguals did not differ in cortical thickness in any region. Our results show that learning a second language after gaining proficiency in the first language modifies brain structure in an age-dependent manner whereas simultaneous acquisition of two languages has no additional effect on brain development.

Bilingual brain organization: A functional magnetic resonance adaptation study

We used functional magnetic resonance adaptation (fMRA) to examine whether intra-voxel functional specificity may be present for first (L1)- and second (L2)-language processing. We examined within- and across-language adaptation for spoken words in English-French bilinguals who had acquired their L2 after the age of 4 years. Subjects listened to words presented binaurally through earphones. In two control conditions (one for each language), six identical words were presented to obtain maximal adaptation. The remaining six conditions each consisted of five words that were identical followed by a sixth word that differed. There were thus a total of eight experimental conditions: no-change (sixth word identical to first five); a change in meaning (different final word in L1); a change in language (final item translated into L2); a change in meaning and language (different final word in L2). The same four conditions were presented in L2. The study also included a silent baseline. At the neural level, within- and across-language word changes resulted in release from adaptation. This was true for separate analyses of L1 and L2. We saw no evidence for greater recovery from adaptation in across-language relative to within-language conditions. While many brain regions were common to L1 and L2, we did observe differences in adaptation for forward translation (L1 to L2) as compared to backward translation (L2 to L1). The results support the idea that, at the lexical level, the neural substrates for L1 and L2 in bilinguals are shared, but with some populations of neurons within these shared regions showing language-specific responses.

Word and nonword repetition in bilingual subjects: A PET study

Learning a specific skill during childhood may partly determine the functional organization of the adult brain. This hypothesis led us to study brain activation patterns using positron emission tomography (PET), in which we compared word and nonword repetition in 10 right‐handed native English‐speakers (L1) who were proficient in their second language, French (L2), which was learned after the age of 5 years. Regional cerebral blood flow (rCBF) was measured by the H215O intravenous bolus method with intersubject averaging and coregistration of magnetic resonance and PET images. A comparison of CBF changes when repeating words in L2 with those seen when repeating words in (L1) demonstrated that the pattern of CBF was similar across the two conditions, with several significant CBF differences in the vicinity of the left insular cortex, ventral premotor region, and in the striatum. We hypothesize that these regions are activated when subjects are required to repeat known words, showing increased activity when there are increased articulatory demands imposed by speaking L2. Comparisons of nonword repetition in L1 and L2 revealed increased activity for L2 in the left ventral premotor region and in the cerebellum; rCBF increases were also observed in these regions in both L1 and L2 with increased number of syllables and increased articulatory complexity, suggesting a role for these regions in the complex motor control needed for the production of novel sequences. Hum Brain Mapp, 2005.

Phonological processing in bilingual word recognition

Abstract A model of bilingual word recognition is presented which is derived from current unilingual dual route and verification models. A core feature of this model is that word recognition involves obligatory grapheme-phoneme translation followed by an optional spelling check. The model is able to account for an observed interlingual homophone effect, and successfully predicts the consequences which impaired functioning of this translator would have for a bilingual who is learning to read orthographically deep and shallow languages simultaneously.

Structural brain changes linked to delayed first language acquisition in congenitally deaf individuals.

Early language experience is essential for the development of a high level of linguistic proficiency in adulthood and in a recent functional Magnetic Resonance Imaging (fMRI) experiment, we showed that a delayed acquisition of a first language results in changes in the functional organization of the adult brain (Mayberry et al., 2011). The present study extends the question to explore if delayed acquisition of a first language also modulates the structural development of the brain. To this end, we carried out anatomical MRI in the same group of congenitally deaf individuals who varied in the age of acquisition of a first language, American Sign Language -ASL (Mayberry et al., 2011) and used a neuroanatomical technique, Voxel-Based Morphometry (VBM), to explore changes in gray and white matter concentrations across the brain related to the age of first language acquisition. The results show that delayed acquisition of a first language is associated with changes in tissue concentration in the occipital cortex close to the area that has been found to show functional recruitment during language processing in these deaf individuals with a late age of acquisition. These findings suggest that a lack of early language experience affects not only the functional but also the anatomical organization of the brain.

ERP measures of auditory word repetition and translation priming in bilinguals

Motivated by the demonstration of similarly localized adaptation of the hemodynamic response in a first (L1) and second (L2) language, this study examined event-related brain potentials (ERPs) to spoken words in L1 and L2 in 15 English-French bilinguals. We examined whether the temporal pattern of N400 adaptation due to within-language repetitions (i.e., repetition priming) was similar in L1 and L2 and whether the release from adaptation elicited by a within-language word change was similar. Furthermore, using word changes across language, we examined the phonological mismatch negativity (PMN) and N400 components to determine the kind of information activated during translation priming. In contrast to within-language repetition, we expected between-language repetition (i.e., translations) to be characterized by conceptual rather than lexical/phonological word form priming. Overall, the pattern of adaptation and release from adaptation was similar in L1 and L2, with evidence of delayed semantic analysis in L2 in the form of a later N400 effect. A change in language (L1 to L2) elicited a similar pattern of PMN and N400 activity compared to a within-language change in meaning in L1, suggesting that neither word form nor conceptual information was available on-line for the forward translation. In contrast, the presence of strong PMN but minimal N400 effects for L2-to-L1 translations suggests that conceptual but not phonological information is available on-line for backwards translation. L2 proficiency influenced the extent to which conceptual representations were activated by translations. These data are discussed in light of current models of bilingual word processing and suggest modality differences in the pattern of activation of lexical and conceptual information.

Mapping the unconscious maintenance of a lost first language

Significance Using functional MRI we examined the unconscious influence of early experience on later brain outcomes. Internationally adopted (IA) children (aged 9–17 years), who were completely separated from their birth language (Chinese) at 12.8 mo of age, on average, displayed brain activation to Chinese linguistic elements that precisely matched that of native Chinese speakers, despite the fact that IA children had no subsequent exposure to Chinese and no conscious recollection of that language. Importantly, activation differed from monolingual French speakers with no Chinese exposure, despite all participants hearing identical acoustic stimuli. The similarity between adoptees and Chinese speakers clearly illustrates that early acquired information is maintained in the brain and that early experiences unconsciously influence neural processing for years, if not indefinitely. Optimal periods during early development facilitate the formation of perceptual representations, laying the framework for future learning. A crucial question is whether such early representations are maintained in the brain over time without continued input. Using functional MRI, we show that internationally adopted (IA) children from China, exposed exclusively to French since adoption (mean age of adoption, 12.8 mo), maintained neural representations of their birth language despite functionally losing that language and having no conscious recollection of it. Their neural patterns during a Chinese lexical tone discrimination task matched those observed in Chinese/French bilinguals who have had continual exposure to Chinese since birth and differed from monolingual French speakers who had never been exposed to Chinese. They processed lexical tone as linguistically relevant, despite having no Chinese exposure for 12.6 y, on average, and no conscious recollection of that language. More specifically, IA participants recruited left superior temporal gyrus/planum temporale, matching the pattern observed in Chinese/French bilinguals. In contrast, French speakers who had never been exposed to Chinese did not recruit this region and instead activated right superior temporal gyrus. We show that neural representations are not overwritten and suggest a special status for language input obtained during the first year of development.