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Diffusion weighted imaging evidence of extra-callosal pathways for interhemispheric communication after complete commissurotomy


The integrity of white matter architecture in the human brain is related to cognitive processing abilities. The corpus callosum is the largest white matter bundle interconnecting the two cerebral hemispheres. “Split-brain” patients in whom all cortical commissures have been severed to alleviate intractable epilepsy demonstrate remarkably intact cognitive abilities despite the lack of this important interhemispheric pathway. While it has often been speculated that there are compensatory alterations in the remaining interhemispheric fibers in split-brain patients several years post-commissurotomy, this has never been directly shown. Here we examined extra-callosal pathways for interhemispheric communication in the brain of a patient who underwent complete cerebral commissurotomy using diffusion weighted imaging tractography. We found that compared with a healthy age-matched comparison group, the split-brain patient exhibited increased fractional anisotropy (FA) of the dorsal and ventral pontine decussations of the cortico-cerebellar interhemispheric pathways. Few differences were observed between the patient and the comparison group with respect to FA of other long-range intrahemispheric fibers. These results point to specific cerebellar anatomical substrates that may account for the spared interhemispheric coordination and intact cognitive abilities that have been extensively documented in this unique patient.

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The authors thank Anouk Scheres and Scott Squire for assistance with data collection.


This work was supported by a University of Miami Gabelli Senior Scholar Award, an award from the Canadian Institute for Advanced Research, and National Institute of Mental Health [R01MH107549] to LQU. We also acknowledge the Nathan Kline Institute Enhanced Rockland Sample for the availability of age-matched comparison participants, collected with support from R01MH094639.

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Correspondence to Jason S. Nomi or Lucina Q. Uddin.

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All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. This article does not contain any studies with animals performed by any of the authors.

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Nomi, J.S., Marshall, E., Zaidel, E. et al. Diffusion weighted imaging evidence of extra-callosal pathways for interhemispheric communication after complete commissurotomy. Brain Struct Funct 224, 1897–1909 (2019).

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  • Corpus callosum
  • Structural connectivity
  • Interhemispheric transfer
  • Epilepsy
  • Hemispheric specialization
  • Laterality