Combining diffusion magnetic resonance tractography with stereology highlights increased cross-cortical integration in primates.
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.
Division of Newborn Medicine, Department of Medicine, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, 02115.|Department of Anthropology and Center for the Advanced Study of Human Paleobiology, The George Washington University, Washington, DC, 20052.
Christine J
CJ
Charvet
Fishberg Department of Neuroscience and Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, New York, 10029.
Patrick R
PR
Hof
Department of Anthropology and School of Biomedical Sciences, Kent State University, Kent, Ohio, 44240.
Mary Ann
MA
Raghanti
Department of Radiology, Athinoula A. Martinos Center for Biomedical Research, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts, 02129.
Andre J
AJ
Van Der Kouwe
Department of Anthropology and Center for the Advanced Study of Human Paleobiology, The George Washington University, Washington, DC, 20052.
Chet C
CC
Sherwood
Division of Newborn Medicine, Department of Medicine, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, 02115.|Department of Radiology, Athinoula A. Martinos Center for Biomedical Research, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts, 02129.
Emi
E
Takahashi
D000818:Animals; D056324:Diffusion Tensor Imaging; D008279:Magnetic Resonance Imaging; D019579:Neocortex / Q000033:anatomy & histology*; D009434:Neural Pathways / Q000033:anatomy & histology*; D011323:Primates
RRID:SCR_001905; RRID:SCR_002526; RRID:SCR_004817; RRID:SCR_012324; connections; cortex; evolution