Statistical sulcal shape comparisons: Application to the detection of genetic encoding of the central sulcus shape

Principal Component Analysis allows a quantitative description of shape var iability with a restricted number of parameters (or modes) which can be use d to quantify the difference between two shapes through the computation of a modal distance. A statistical test can then be applied to this set of mea surements in order to detect a statistically significant difference between two groups. We have applied this methodology to highlight evidence of gene tic encoding of the shape of neuroanatomical structures. To investigate gen etic constraint, we studied if shapes were more similar within 10 pairs of monozygotic twins than within interpairs and compared the results with thos e obtained from 10 pairs of dizygotic twins. The statistical analysis was p erformed using a Mantel permutation test. We show, using simulations, that this statistical test applied on modal distances can detect a possible gene tic encoding. When applied to real data, this study highlighted genetic con straints on the shape of the central sulcus. We found from 10 pairs of mono zygotic twins that the intrapair modal distance of the central sulcus was s ignificantly smaller than the interpair modal distance, for both the left c entral sulcus (Z = -2.66; P < 0.005) and the right central sulcus (Z = -2.2 6; P < 0.05). Genetic constraints on the definition of the central sulcus s hape were confirmed by applying the same experiment to 10 pairs of normal y oung individuals (Z = -1.39; Z = -0.63, i.e., values not significant at the P < 0.05 level) and 10 pairs of dizygotic twins (Z = 0.47; Z = 0.03, i.e., values not significant at the P < 0.05 level). (C) 2000 Academic Press.