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Electronic Letters to:
- Brief Communications:
James M. Johnston, S. Neil Vaishnavi, Matthew D. Smyth, Dongyang Zhang, Biyu J. He, John M. Zempel, Joshua S. Shimony, Abraham Z. Snyder, and Marcus E. Raichle- Loss of Resting Interhemispheric Functional Connectivity after Complete Section of the Corpus Callosum
J. Neurosci. 2008; 28: 6453-6458[Abstract] [Full text] [PDF]
eLetters: Submit a response to this article
Electronic letters published:
Interhemispheric resting-state functional connectivity: insights from the split-brain
- Lucina Q. Uddin (26 June 2008)
Interhemispheric resting-state functional connectivity: insights from the split-brain 26 June 2008 
Lucina Q. Uddin,
postdoctoral researcher
Stanford University, Palo Alto, CA 94304Send letter to journal:
Re: Interhemispheric resting-state functional connectivity: insights from the split-brain
lucina.uddin{at}gmail.com Lucina Q. Uddin
This paper uses sophisticated methods to make a significant contribution to the rapidly evolving field of resting-state functional connectivity. Its strengths include the analysis of both pre-and post surgical data on a unique patient, which affords the opportunity to directly test the hypothesis that interruption of anatomical connections affects functional connectivity between the cerebral hemispheres.
The major limitation of the paper, which the authors acknowledge, is the possibility that the results reported reflect an acute post-surgical effect, rather than a persistent phenomenon. The possibility of compensatory reorganization is very likely, given the subject's young age. An important study to conduct would be a long-term follow up of this patient in several years, to investigate the effects of plasticity and reorganization on interhemispheric connectivity. In a recently published study we report data from an adult split-brain patient, tested 44 years post-surgery. This patient exhibited a strong degree of residual functional connectivity between homologous regions in the left and right hemispheres. When compared to a group of 42 neurologically intact adult participants, our patient showed interhemispheric correlation scores that fell within the range of scores obtained from typical adults, despite complete transection of the corpus callosum, hippocampal commissure, anterior commissure, and massa intermedia. We concluded that this evidence of bilateral resting-state networks in a complete commisurotomy patient suggests a subcortical (e.g. brainstem) origin for low-frequency BOLD fluctuations (Uddin et al., 2008). Another relevant study reports data from a minimally conscious patient suffering acute brainstem ischaemia. This patient exhibited an absence of interhemispheric functional connectivity at rest, leading the authors to suggest "a role for ascending transmitter systems in maintaining coherent low-frequency oscillations in bilaterally homologous cortical regions" (Salvador et al., 2005). I suggest that by examining patients without a corpus callosum at various stages of post-surgical recovery, as well as patients with brainstem lesions, we may eventually arrive at a clearer picture of the exact contribution of distinct anatomical pathways to specific resting- state networks.
Salvador R, Suckling J, Coleman MR, Pickard JD, Menon D, Bullmore E (2005) Neurophysiological architecture of functional magnetic resonance images of human brain. Cereb Cortex 15:1332-1342.
Uddin LQ, Mooshagian E, Zaidel E, Scheres A, Margulies DS, Kelly AM, Shehzad Z, Adelstein JS, Castellanos FX, Biswal BB, Milham MP (2008) Residual functional connectivity in the split-brain revealed with resting-state functional MRI. Neuroreport 19:703-709.
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