The Contribution of the Corpus Callosum to Language Lateralization.
The development of hemispheric lateralization for language is poorly understood. In one hypothesis, early asymmetric gene expression assigns language to the left hemisphere. In an alternate view, language is represented a priori in both hemispheres and lateralization emerges via cross-hemispheric communication through the corpus callosum. To address this second hypothesis, we capitalized on the high temporal and spatial resolution of magnetoencephalographic imaging to measure cortical activity during language processing, speech preparation, and speech execution in 25 participants with agenesis of the corpus callosum (AgCC) and 21 matched neurotypical individuals. In contrast to strongly lateralized left hemisphere activations for language in neurotypical controls, participants with complete or partial AgCC exhibited bilateral hemispheric activations in both auditory or visually driven language tasks, with complete AgCC participants showing significantly more right hemisphere activations than controls or than individuals with partial AgCC. In AgCC individuals, language laterality positively correlated with verbal IQ. These findings suggest that the corpus callosum helps to drive language lateralization.


CONCLUSIONS
The role that corpus callosum development has on the hemispheric specialization of language is poorly understood. Here, we used magnetoencephalographic imaging during linguistic tests (verb generation, picture naming) to test for hemispheric dominance in patients with agenesis of the corpus callosum (AgCC) and found reduced laterality (i.e., greater likelihood of bilaterality or right hemisphere dominance) in this cohort compared with controls, especially in patients with complete agenesis. Laterality was positively correlated with behavioral measures of verbal intelligence. These findings provide support for the hypothesis that the callosum aids in functional specialization throughout neural development and that the loss of this mechanism correlates with impairments in verbal performance.
Department of Radiology and Biomedical Imaging.
Leighton B N
LB
Hinkley
Department of Neurology, Department of Pediatrics, and.
Elysa J
http://orcid.org/0000-0002-5284-9888
EJ
Marco
Department of Radiology and Biomedical Imaging.
Ethan G
EG
Brown
Department of Neurology.
Polina
P
Bukshpun
Department of Neurology.
Jacquelyn
J
Gold
Department of Radiology and Biomedical Imaging.
Susanna
S
Hill
Department of Radiology and Biomedical Imaging.
Anne M
http://orcid.org/0000-0003-1002-4391
AM
Findlay
Clinical and Translational Science Institute-Pediatric Clinical Research Center, University of California, San Francisco, California 94143.
Rita J
http://orcid.org/0000-0002-2460-9887
RJ
Jeremy
Department of Neurology.
Mari L
ML
Wakahiro
Department of Radiology and Biomedical Imaging, Department of Neurology, Department of Pediatrics, and.
A James
http://orcid.org/0000-0003-4291-7346
AJ
Barkovich
Department of Radiology and Biomedical Imaging.
Pratik
http://orcid.org/0000-0001-7473-7409
P
Mukherjee
Department of Neurology, Department of Pediatrics, and sri@radiology.ucsf.edu sherre@neuropeds.ucsf.edu.
Elliott H
http://orcid.org/0000-0002-4118-5385
EH
Sherr
Department of Radiology and Biomedical Imaging, sri@radiology.ucsf.edu sherre@neuropeds.ucsf.edu.
Srikantan S
http://orcid.org/0000-0001-7209-3857
SS
Nagarajan
D000161:Acoustic Stimulation / Q000379:methods; D000293:Adolescent; D000328:Adult; D061085:Agenesis of Corpus Callosum / Q000175:diagnosis / Q000503:physiopathology*; D015331:Cohort Studies; D003337:Corpus Callosum / Q000502:physiology*; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D007802:Language; D015225:Magnetoencephalography / Q000379:methods; D008297:Male; D008875:Middle Aged; D011597:Psychomotor Performance / Q000502:physiology; D013060:Speech / Q000502:physiology*; D055815:Young Adult
corpus callosum; hemispheric specialization; language; magnetoencephalography