This pattern of anatomical connectivity was confirmed with RSFC in the VX-765 mouse human brain and clearly sets ventral area 6 apart from areas 44 and 45. As can be seen in Fig. 1, the functional connectivity of area 6 was restricted to the anterior

part of the supramarginal gyrus that is delimited by the posterior ascending ramus of the Sylvian fissure. The pattern of RSFC associated with Cluster 3 (Fig. 5) supports this conclusion, which was also confirmed by the direct contrasts between BA 6, and BAs 44 and 45 (as shown in Fig. 1 and Table 1). The strong RSFC of BA 6 with the most anterior part of the inferior parietal lobule and the absence of correlations with the posterior part of the supramarginal gyrus and the angular gyrus define a unique profile of parietal RSFC for ventral BA 6. By contrast, areas 44 and 45 exhibited a functional connectivity pattern with the posterior supramarginal gyrus and the angular gyrus (Fig. 1), consistent with predictions this website from the macaque monkey studies (Petrides & Pandya, 2009). Furthermore, areas 44 and 45 had strong correlations with the cortex in the superior temporal sulcus and the temporal cortex just below it, namely the middle temporal gyrus (Figs 1 and 2). The strong distinction between the connectivity patterns associated with ventral area 6 relative to areas 44 and 45 is most evident in the results of the clustering analysis. The simplest

and most robust partitioning of the data (K = 2, see Fig. 3) was one that separated ventral area 6 into one cluster, and areas 44, 45 and the rest of the inferior frontal gyrus into another (see top row of Fig. 4). The clear separation Thalidomide between ventral area 6 and area 44 anteriorly was also present for the optimal solution (K = 4, see Fig. 4). In both monkey and human brains, ventral area 6 is a typical premotor cortex that lacks layer IV, whereas area 45 is a typical prefrontal

cortex with a well-developed layer IV (Brodmann, 1909; Amunts et al., 1999; Petrides & Pandya, 2002). Area 44, which lies between areas 6 and 45, does possess a layer IV, but it is interrupted and not well developed. Consequently, there has long been confusion as to whether BA 44 should be considered a premotor zone that is functionally similar to premotor cortex or whether BA 44 is functionally more similar to prefrontal BA 45. For instance, some investigators have considered Broca’s region to include both BAs 44 and 45 (Amunts et al., 1999) while others have restricted it to BA 44 (Mohr et al., 1978). The present results address this issue. The functional connectivity patterns of BAs 44 and 45, which together comprise Broca’s area, were more similar to one another than to the RSFC of ventral BA 6. This conclusion is also consistent with a study by Amunts & Zilles (2006), who examined the architectonic and neurochemical profiles of BA 44 and concluded that it shares more features with BA 45 than with BA 6.