A recent study about the neurobiological mechanisms underlying language processes has focused on behavioural-cognitive aspects and functional neuroimaging (fMRI) in bilingual subjects. fMRI technique is based on changes of cerebral blood flow that are linked with the regional cerebral activation associated with the execution of motor, sensory and cognitive tasks.
Previous studies have contributed to the realization of a functional map of cerebral circuits responsible for the elaboration of the main levels of linguistic organization.
Our group studied the neural correlates of semantic and grammatical representations by using functional neuroimanging, during paradigms of linguistic activation in bilingual subjects. Aim was to test the role of crucial variables, such as age of acquisition, proficiency level, and daily usage of a language, in determining the cerebral language systems in bilingual subjects. Recent studies have shown that there are regions activated by first language, and not necessarily by a second language, mainly if this was learned later in life and with less attained proficiencies, while with high proficiency level the neural substrates become comparable (Perani et al 96,98).
In this collaboration with the Berlin University, we evaluated 3 groups of Italian German bilinguals: the first group had acquired both languages since birth, with parents speaking one and/or the other language, and with constant exposure and usage of both languages. This first group therefore had high proficiency and a parallel and early acquisition of both languages. The second group had attained a high proficiency for both languages, but had learned the second after the age of 10 years; the third group had learned the second language later in life and with less attained proficiency: therefore these were bilinguals with late acquisition and low proficiency. The study has shown how important the age of acquisition is, because the earliest the acquisition, the most comparable are the neural substrates responsible for language processing of the two languages. Only in the first group the neural systems involved in executing grammatical and semantic tasks were comparable for Italian and German, while in the second group, the second language, although having attained the same proficiency, required a more extensive cerebral activation. This effect was further evident for the third group made by late, low proficient bilinguals. Thus, syntactic and semantic processes require a parallel acquisition of the two languages since birth to obtain a comparable underlying neural substrate. The pattern of neural activation is thus to be considered age-dependent. These functional differences can be interpreted also on the basis of a "critical period" for second language acquisition, depending on the characteristics of our central nervous system. Only a second language acquired very early in life accessed the same neural substrates for grammatical processing as the first language. Proficiency was the main determinant of grammar and semantics in late language acquisition. Thus these findings support the existence of a 'critical period' for language acquisition suggesting that grammatical processing, given its dependence on age of acquisition, is based on competence, which is neurologically 'wired-in'. The results of this research have been published on the authoritative scientific journal Neuron (Wartemburger et al. 03). This research tells us mainly that we should learn languages as soon as possible, with a continual and prolonged exposure. A Babel of languages for Europe, but most of them spoken by everyone!
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