Colateralization of Broca's area and the visual word form area in left-handers: fMRI evidence |
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Authors: | Van der Haegen Lise Cai Qing Brysbaert Marc |
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Institution: | Department of Experimental Psychology, Ghent Institute for Functional and Metabolic Imaging, Ghent University, Belgium |
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Abstract: | Language production has been found to be lateralized in the left hemisphere (LH) for 95% of right-handed people and about 75% of left-handers. The prevalence of atypical right hemispheric (RH) or bilateral lateralization for reading and colateralization of production with word reading laterality has never been tested in a large sample. In this study, we scanned 57 left-handers who had previously been identified as being clearly left (N = 30), bilateral (N = 7) or clearly right (N = 20) dominant for speech on the basis of fMRI activity in the inferior frontal gyrus (pars opercularis/pars triangularis) during a silent word generation task. They were asked to perform a lexical decision task, in which words were contrasted against checkerboards, to test the lateralization of reading in the ventral occipitotemporal region. Lateralization indices for both tasks correlated significantly (r = 0.59). The majority of subjects showed most activity during lexical decision in the hemisphere that was identified as their word production dominant hemisphere. However, more than half of the sample (N = 31) had bilateral activity for the lexical decision task without a clear dominant role for either the LH or RH, and three showed a crossed frontotemporal lateralization pattern. These findings have consequences for neurobiological models relating phonological and orthographic processes, and for lateralization measurements for clinical purposes. |
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Keywords: | Broca&rsquo s area Cerebral lateralization fMRI Reading Speech Ventral occipito-temporal (vOT) activity Visual word form area (VWFA) |
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