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Comparing the shape variability of cortical sulci in hominids

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Foubet, Ophelie | Sun, Zhong, Yi | Mangin, Jean-Francois | Hopkins, William, D

Edité par CCSD -

International audience. Gyrification of the neocortex occurs during the third trimester of gestation in humans. The pattern of folding that occurs during this phenomenon is not random, but linked to internal structural and functional organization [1,2]. Some patterns can be shared between species, such as the central (CS) and precentral (preCS) sulci in great apes, which form the boundaries of the precentral gyrus, seat of the motor cortex (BA 4, and part of BA6) [3].Here, we examined inter-individual variability in the shape of the central and precentral sulci (CS and preCS) in humans, chimpanzees, gorillas and orangutans (pongos).Using Morphologist from the BrainVISA pipeline [4], which extracts sulci from T1-weighted MRI images, we compare pairwise sulci shape after rigid alignment and normalization by species-specific homotheticity. We reduce the space covered by the sulci set using the isomap algorithm and calculate moving averages to display the shape variability trait expressed on each isomap axis. Our results show that chimpanzees capable of making sounds to attract a human's attention (Attention Getting Sound, AG +) have a pre-central gyrus with a longer orofacial area than others.In fact, studying the pre-central gyrus by selecting the CS and preCS provides more information in the analysis of motor areas. Whereas the central sulcus only provides information on its adjacent primary motor cortex, selecting the precentral gyrus also provides information on the premotor cortex located between the two. We can see that this new analysis of the precentral gyrus brings an asymmetry between the hemispheres in humans in dimension 1 of the comparison between humans and chimpanzees. And it brings an asymmetry between chimpanzee hemispheres in dimension 2.Our results also show that different gorilla species, mountain or lowland, express a significantly different shape of their hand region, suggesting an evolutionary effect of the environment on the morphology of the hand region.Finally, we show that the anatomical comparison of species can be made at the level of their sulcus shape, an expression of underlying structural and functional differences.This is useful for studying inter-individual variations, but also from an evolutionary point of view.

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