Looking at Second Language Acquisition from a Functional- and Structural MRI Background

Looking at Second Language Acquisition from a Functional- and Structural MRI Background Maurits van den Noort (Maurits.Noort@psybp.uib.no) Department of Biological and Medical Psychology, Jonas Lies vei 91 Bergen, N-5009 Norway Peggy Bosch (Pbosch@online.no) Department of Psychiatry and Clinical Medicine, Sandviksleitet 1 Bergen, N-5035 Norway Kenneth Hugdahl (Hugdahl@psybp.uib.no) Department of Biological and Medical Psychology, Jonas Lies vei 91 Bergen, N-5009 Norway Abstract The question how second and/or third languages are represented in the brain has been the focus of many neuroimaging studies. Some investigators found at least partly different representations for different languages; others reported findings that do not support the hypothesis that different languages are represented in distinct brain regions. However, these different findings can often be explained by differences in experimental set up and by the selection of the bilingual- and multilingual participants. Recently, structural MRI has been used for second language research, as well. Can structural MRI give us a better understanding of the mechanisms behind second and/or third language acquisition? In this paper, functional- and structural neuroimaging data will be discussed in order to answer that question. Keywords: second language acquisition; functional MRI; PET; structural MRI. Language Representation An important question that is asked in many studies is how second and/or third languages are represented in the brain. A major hypothesis is that, in bilinguals and polyglots, the different languages are represented and processed in distinct brain regions. Some indirect evidence for this hypothesis has been found in bilinguals and/or polyglots suffering from aphasia (Paradis, 1989). It was occasionally observed that only one of the mastered languages was affected (Albert & Obler, 1978; Paradis, 1995). Moreover, it is not unusual to find that different languages recover to different degrees or even that there is an antagonistic pattern of recovery between two languages (Paradis, 1977). Neurosurgery as well, may lead to a selective impairment of one language in bilinguals (Gomez-Tortosa et al., 1995). Finally, more evidence in favour of this hypothesis was found in electrical stimulation studies. These studies showed that in multilingual speakers, different languages may be disrupted selectively (Black & Ronner, 1987; Ojemann & Whitaker, 1978; Roux & Tremoulet, 2002). Recently, PET and fMRI have allowed a more direct study of the neural representation of language in bilinguals and polyglots. However, the pattern that emerges from these neuroimaging studies is far from consistent. In some studies (Dehaene et al., 1997; Kim et al., 1997; Perani et al., 1996; Yetkin et al., 1996), at least partly different representations for different languages were found. In other studies (Hasegawa, Carpenter, & Just, 2002; Hernandez, Dapretto, & Mazziotta, 2001; Illes et al., 1999; Klein et al., 1995) no evidence was found that languages are represented in distinct brain regions. In a few studies (Chee, Tan, & Thiel, 1999; Klein et al., 1999; Pu et al., 2001; Vingerhoets et al., 2003), shared neural substrates were found (Van den Noort et al., 2005b). Evidently, more research is necessary before any firm conclusions can be drawn. The pattern that emerges from functional neuroimaging studies is far from consistent, which can partially be explained by two major problems: 1) Researchers use different kinds of experimental paradigms, making comparisons between bilingual- and multilingual studies very difficult. 2) The selection of the participants differs. As a result, most of the differences that are found in neuroimaging studies can be explained by differences of the proficiency level, second language onset, and second language exposure of the bilingual- and multilingual participants (Indefrey, to appear). Nevertheless, there are reliable differences between the hemodynamic activation patterns observed during L1 and L2 language processing, but only for subgroups of bilingual speakers and predominantly in the direction of stronger activation during L2 processing (Abutalebi, Cappa, & Perani, 2001; Indefrey, to appear; Stowe & Sabourin, 2005). Structural Brain Changes Inferior Parietal Region Recently, structural MRI has been used for second language research, as well (Van den Noort, Bosch, & Hugdahl, 2005a). It is important to note that structural MRI is not a