Evolution amplified processing with temporally dispersed slow neuronal connectivity in primates
- aDepartment of Physiology and Pharmacology, University of Rome La Sapienza, 00185 Rome Italy;
- bLaboratory of Non Linear Systems, School of Information and Communication Sciences, Swiss Federal Institute of Technology, 1015 Lausanne, Switzerland;
- cDepartment of Biology, Technische Universitaet Darmstadt, 64287 Darmstadt, Germany;
- dDepartment of Neuroscience, Mount Sinai School of Medicine, New York, NY 10029; and
- eDepartment of Neuroscience, Karolinska Institutet, S-171 77, Stockholm, Sweden
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Edited by Jon H. Kaas, Vanderbilt University, Nashville, TN, and approved September 10, 2009 (received for review July 10, 2009)
Abstract
The corpus callosum (CC) provides the main route of communication between the 2 hemispheres of the brain. In monkeys, chimpanzees, and humans, callosal axons of distinct size interconnect functionally different cortical areas. Thinner axons in the genu and in the posterior body of the CC interconnect the prefrontal and parietal areas, respectively, and thicker axons in the midbody and in the splenium interconnect primary motor, somatosensory, and visual areas. At all locations, axon diameter, and hence its conduction velocity, increases slightly in the chimpanzee compared with the macaque because of an increased number of large axons but not between the chimpanzee and man. This, together with the longer connections in larger brains, doubles the expected conduction delays between the hemispheres, from macaque to man, and amplifies their range about 3-fold. These changes can have several consequences for cortical dynamics, particularly on the cycle of interhemispheric oscillators.
Footnotes
- 1To whom correspondence should be addressed. E-mail: giorgio.innocenti{at}ki.se
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Author contributions: G.M.I. designed research; R.C., R.G., and P.R.H. performed research; H.G., R.G., and G.M.I. analyzed data; and R.G., P.R.H., and G.M.I. wrote the paper.
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The authors declare no conflict of interest.
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This article is a PNAS Direct Submission.
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This article contains supporting information online at www.pnas.org/cgi/content/full/0907655106/DCSupplemental.
