title: Gaussian mixture modeling of hemispheric lateralization for language in a large sample of healthy individuals balanced for handedness.
abstract: Hemispheric lateralization for language production and its relationships with manual preference and manual preference strength were studied in a sample of 297 subjects, including 153 left-handers (LH). A hemispheric functional lateralization index (HFLI) for language was derived from fMRI acquired during a covert sentence generation task as compared with a covert word list recitation. The multimodal HFLI distribution was optimally modeled using a mixture of 3 and 4 Gaussian functions in right-handers (RH) and LH, respectively. Gaussian function parameters helped to define 3 types of language hemispheric lateralization, namely "Typical" (left hemisphere dominance with clear positive HFLI values, 88% of RH, 78% of LH), "Ambilateral" (no dominant hemisphere with HFLI values close to 0, 12% of RH, 15% of LH) and "Strongly-atypical" (right-hemisphere dominance with clear negative HFLI values, 7% of LH). Concordance between dominant hemispheres for hand and for language did not exceed chance level, and most of the association between handedness and language lateralization was explained by the fact that all Strongly-atypical individuals were left-handed. Similarly, most of the relationship between language lateralization and manual preference strength was explained by the fact that Strongly-atypical individuals exhibited a strong preference for their left hand. These results indicate that concordance of hemispheric dominance for hand and for language occurs barely above the chance level, except in a group of rare individuals (less than 1% in the general population) who exhibit strong right hemisphere dominance for both language and their preferred hand. They call for a revisit of models hypothesizing common determinants for handedness and for language dominance.
authors: Groupe d'Imagerie Neurofonctionnelle, Centre National de la Recherche Scientifique, Commissariat à l'Energie Atomique, et Université de Bordeaux, Bordeaux, France.
authors: Bernard
authors: B
authors: Mazoyer
authors: Groupe d'Imagerie Neurofonctionnelle, Centre National de la Recherche Scientifique, Commissariat à l'Energie Atomique, et Université de Bordeaux, Bordeaux, France.
authors: Laure
authors: L
authors: Zago
authors: Groupe d'Imagerie Neurofonctionnelle, Centre National de la Recherche Scientifique, Commissariat à l'Energie Atomique, et Université de Bordeaux, Bordeaux, France.
authors: Gaël
authors: G
authors: Jobard
authors: Groupe d'Imagerie Neurofonctionnelle, Centre National de la Recherche Scientifique, Commissariat à l'Energie Atomique, et Université de Bordeaux, Bordeaux, France.
authors: Fabrice
authors: F
authors: Crivello
authors: Groupe d'Imagerie Neurofonctionnelle, Centre National de la Recherche Scientifique, Commissariat à l'Energie Atomique, et Université de Bordeaux, Bordeaux, France.
authors: Marc
authors: M
authors: Joliot
authors: Groupe d'Imagerie Neurofonctionnelle, Centre National de la Recherche Scientifique, Commissariat à l'Energie Atomique, et Université de Bordeaux, Bordeaux, France.
authors: Guy
authors: G
authors: Perchey
authors: Groupe d'Imagerie Neurofonctionnelle, Centre National de la Recherche Scientifique, Commissariat à l'Energie Atomique, et Université de Bordeaux, Bordeaux, France.
authors: Emmanuel
authors: E
authors: Mellet
authors: Groupe d'Imagerie Neurofonctionnelle, Centre National de la Recherche Scientifique, Commissariat à l'Energie Atomique, et Université de Bordeaux, Bordeaux, France.
authors: Laurent
authors: L
authors: Petit
authors: Groupe d'Imagerie Neurofonctionnelle, Centre National de la Recherche Scientifique, Commissariat à l'Energie Atomique, et Université de Bordeaux, Bordeaux, France.
authors: Nathalie
authors: N
authors: Tzourio-Mazoyer
mesh_terms: D000293:Adolescent; D000328:Adult; D001519:Behavior; D003071:Cognition; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D064368:Healthy Volunteers; D006801:Humans; D007802:Language; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D008959:Models, Neurological; D016011:Normal Distribution; D018401:Sample Size; D057566:Self Report; D012660:Semantics; D017585:Ultrasonography, Doppler, Transcranial; D055815:Young Adult