Abstract
A recent study of the corpus callosum (CC) in humans revealed a new topographical arrangement of the cortical connectivity pattern. To explore the CC topography in nonhuman primates, we applied magnetic resonance diffusion tensor imaging and tract tracing techniques in individual rhesus monkeys in vivo. The results demonstrate that the CC topography of primates and humans is surprisingly similar. In particular, the relatively large representation and caudal extension of commissural frontal fibers in the CC is observed in both the monkey and human brain. If evolutionary changes in relative brain volumes are reflected in the arrangement of related fibers crossing the CC, the current study is in line with the fact that the relative volume of the frontal lobe did not significantly increase after the split of the hominid line from other primates.
Highlights
The corpus callosum (CC) serves as the major connection between the 2 cortical hemispheres in placental mammals
Extending other primate studies (LaMantia and Rakic 1990a, 1990b), we could analyze the monkey CC in vivo and with a diffusion tensor imaging (DTI) technique not hampered by geometric distortions due to tissue susceptibility differences (Nolte et al 2000; Rieseberg et al 2005)
Because of the high spatial resolution of the anatomic and diffusion-weighted images, fiber tracts of the macaque CC were derived in anatomically correct appearance similar to what has previously been accomplished for the human brain (Hofer and Frahm 2006)
Summary
The corpus callosum (CC) serves as the major connection between the 2 cortical hemispheres in placental mammals. Sectors 6 and 7 (posterior midbody) comprising fibers from primary and secondary somatosensory cortices and sector 10 (posterior splenium) containing fibers from the visual cortex are characterized by large and very large fibers with diameters of 2.5 lm or more (LaMantia and Rakic 1990a). This pattern of regional differentiation derived from electron microscopy studies of monkey tissue (LaMantia and Rakic 1990b) agrees with corresponding findings of Aboitiz et al (1992) reported for humans
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