title: Colateralization of Broca's area and the visual word form area in left-handers: fMRI evidence.
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.
authors.affiliation: Department of Experimental Psychology, Ghent Institute for Functional and Metabolic Imaging, Ghent University, Belgium. Lise.VanderHaegen@UGent.be
authors.forename: Lise
authors.initials: L
authors.lastname: Van der Haegen
authors.forename: Qing
authors.initials: Q
authors.lastname: Cai
authors.forename: Marc
authors.initials: M
authors.lastname: Brysbaert
mesh_terms: D001931:Brain Mapping; D005260:Female; D005625:Frontal Lobe / Q000502:physiology*; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011932:Reading; D013060:Speech