3C. To discern the most stable pattern of cluster assignment across subjects, we applied the spectral clustering algorithm to the consensus matrices and computed the modified silhouette. Figure 3F plots the modified silhouette values, and suggests that, across subjects, the most stable pattern of cluster assignment is for K = 4. Qualitatively, the surface maps for the solutions computed on the basis of the consensus matrix are highly ABT-263 datasheet similar to those computed on the basis of the group-average η2 matrix (Fig. 4), and the VI metric demonstrates that

the best similarity between the clustering solutions is for K = 2 : 4 (Fig. 3G). On the basis of the clustering analyses, we concluded that K = 4 represented the most favorable solution (see Fig. 4). Qualitatively, the four clusters were located in the superior part of the inferior frontal gyrus, bordering the inferior

frontal sulcus (Cluster 1), the lateral pars opercularis Selleck Tanespimycin and pars triangularis (Cluster 2), inferior precentral cortex (Cluster 3) and a fourth region extending medially within the Sylvian fissure from the inferior-most tip of the ventral premotor cortex and the pars opercularis towards the anterior insula (Cluster 4). To verify these clusters as functionally distinct regions of ventrolateral frontal cortex, we examined the RSFC associated with four spherical seed ROIs of 4-mm radius, centered on the centers-of-mass of each of the clusters of the group-average

K = 4 spectral clustering solution. Figure 5 shows the group-level (Z > 2.3; cluster significance P < 0.05, corrected) RSFC for each of the four 17-DMAG (Alvespimycin) HCl clusters, as well as direct comparisons between clusters. The pattern of RSFC observed for Cluster 2, which includes the central parts of the pars opercularis and pars triangularis, is very similar to those observed for ROIs based in BAs 44 and 45 (compare Cluster 2 in Fig. 5 with BA 44 and 45 in Fig. 1). Similarly, the pattern of RSFC for Cluster 3, which includes the inferior part of the precentral gyrus, is consistent with that for the ROI based in BA 6 (compare Cluster 3 in Fig. 5 with BA 6 in Fig. 1). The voxels in Cluster 1 probably separate from the rest of the large ventrolateral frontal region of interest that was defined for the clustering analysis by virtue of the fact that they are located along the inferior frontal sulcus on the border with the middle frontal gyrus, which would include voxels of areas 8 and 9/46v in the upper bank of the inferior frontal sulcus and adjacent middle frontal gyrus. Specifically, Cluster 1 exhibited RSFC with almost all of the inferior frontal gyrus, anterior to and including the inferior precentral sulcus, dorsal BA 6 and BA 8 in the middle frontal gyrus, the intraparietal sulcus, and the caudal middle and inferior temporal cortex. The comparison Cluster 1 > Cluster 2 (Fig.