Bilingual and multilingual language processing

This chapter addresses the interesting question on the neurolinguistics of bilingualism and the representation of language in the brain in bilingual and multilingual subjects. A fundamental issue is whether the cerebral representation of language in bi- and multilinguals differs from that of monolinguals, and if so, in which specific way. This is an interdisciplinary question which needs to identify and differentiate different levels involved in the neural representation of languages, such as neuroanatomical, neurofunctional, biochemical, psychological and linguistic levels. Furthermore, specific factors such as age, manner of acquisition and environmental factors seem to affect the neural representation. We examined the question whether verbal memory processing in two unrelated languages is mediated by a common neural system or by distinct cortical areas. Subjects were Finnish-English adult multilinguals who had acquired the second language after the age of ten. They were PET-scanned whilst either encoding or retrieving word pairs in their mother tongue (Finnish) or in a foreign language (English). Within each language, subjects had to encode and retrieve four sets of 12 visually presented paired word associates which were not semantically related. Two sets consisted of highly imaginable words and the other two sets of abstract words. Presentation of pseudo-words served as a reference condition. An emission scan was recorded after each intravenous administration of O-15 water. Encoding was associated with prefrontal and hippocampal activation. During memory retrieval, precuneus showed a consistent activation in both languages and for both highly imaginable and abstract words. Differential activations were found in Broca's area and in the cerebellum as well as in the angular/supramarginal gyri according to the language used. The findings advance our understanding of the neural representation that underlies multiple language functions. Further studies are needed to elucidate the neuronal mechanisms of bi/multilingual language processing. A promising perspective for future bi/multilingual research is an integrative approach using brain imaging studies with a high spatial resolution such as fMRI, combined with techniques with a high temporal resolution, such as magnetoencephalography (MEG).