Ontogenetic pattern of gyrification in fetuses of cynomolgus monkeys.

The ontogenetic pattern of gyrification and its relationship with cerebral cortical volume were examined in cynomolgus monkey fetuses. T(1)-weighted coronal magnetic resonance (MR) images at 7 T were acquired from the fixed cerebra of three male fetuses, each at embryonic days (EDs) 70 to 150, and the gyrification index (GI) of each slice was estimated. The mean GI was low (1.1-1.2) during EDs 70 to 90, and then increased dramatically on ED 100. The developmental profiles of the rostrocaudal GI distribution revealed that cortical convolution was more frequent in the parietooccipital region than in other regions during EDs 100 to 150, forming an adult-like pattern by ED 150. The mean GI was closely correlated with the volume of cortical gray matter (r=0.9877), and also with the volume of white matter/intermediate zone (r=0.8961). These findings suggest that cortical convolution is correlated with either the maturation of cortical gray matter or the development of white matter bundles. The characteristic GI distribution pattern of catarrhines was formed by ED 150 in correlation with the progressive sulcal infolding in the parietooccipital region of the cerebrum.