PET studies on the memory processing of word pairs in bilingual Finnish–English subjects

This study examined the fundamental question whether verbal memory processing in two unrelated languages is mediated by a common neural system or by distinct cortical areas. Ten right-handed, male Finnish--English adult late bilinguals who had acquired the second language after the age of 10 were scanned whilst either encoding/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 imageable words (e.g. monkey-table; koira-lasi) and the other two sets of abstract word pairs (e.g. freedom-moral; uhka-suure). Presentation of pseudowords 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 imageable and abstract words. Although the brain mechanisms of the two languages share common components, 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.