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Combining diffusion magnetic resonance tractography with stereology highlights increased cross‐cortical integration in primates
Author(s) -
Charvet Christine J.,
Hof Patrick R.,
Raghanti Mary Ann,
Kouwe Andre J.,
Sherwood Chet C.,
Takahashi Emi
Publication year - 2017
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.24115
Subject(s) - tractography , biology , neuroscience , diffusion mri , stereology , anatomy , cortex (anatomy) , magnetic resonance imaging , medicine , radiology , endocrinology
The isocortex of primates is disproportionately expanded relative to many other mammals, yet little is known about what the expansion of the isocortex entails for differences in cellular composition and connectivity patterns in primates. Across the depth of the isocortex, neurons exhibit stereotypical patterns of projections. Upper‐layer neurons (i.e., layers II–IV) project within and across cortical areas, whereas many lower‐layer pyramidal neurons (i.e., layers V–VI) favor connections to subcortical regions. To identify evolutionary changes in connectivity patterns, we quantified upper (i.e., layers II–IV)‐ and lower (i.e., layers V–VI)‐layer neuron numbers in primates and other mammals such as rodents and carnivores. We also used MR tractography based on high‐angular resolution diffusion imaging and diffusion spectrum imaging to compare anterior‐to‐posterior corticocortical tracts between primates and other mammals. We found that primates possess disproportionately more upper‐layer neurons as well as an expansion of anterior‐to‐posterior corticocortical tracts compared with other mammals. Taken together, these findings demonstrate that primates deviate from other mammals in exhibiting increased cross‐cortical connectivity. J. Comp. Neurol. 525:1075–1093, 2017. © 2016 Wiley Periodicals, Inc.