Figure 4.

Comparison of the lateral pallium (LP) long axis in a rodent (A) and a primate (B). These schemata represent the invariant position of the insular/perirhinal mesocortex (LP) relative to the olfactory cortex (ventral pallium, VP) and the primary septal and amygdalar poles of the hemisphere in a rodent (A) and in a primate (B). The length axis of the rodent LP enclosing the claustroinsular complex is relatively undistorted (gray arrow, A), whereas the length axis of the primate LP undergoes a complex deformation. The frontal tip of LP points into the posterior orbital region of the frontal lobe, its middle part gets bent upon itself to form the insular cortex, and its caudal tip sharply bends around the medial aspect of the temporal pole (gray arrow, B). Note the VP (red) can be easily distinguished underneath the LP (yellow) in rodents (A), while its topologically invariant position is found in the primate along the insular limen and ending caudally next to the uncal amygdalar complex. Consistently with the deformation suffered by the length axis of LP and VP as the temporal lobe emerges, the conserved topologic dorsoventral dimension now points from the insula into the insular limen. By using the septal and amygdalar poles as reference points, it is evident that the LP, which is dorsal to the amygdaloid pole in a rodent, acquires a quite different relative topography in the temporal lobe in primates. In primates, the long axes of both the LP and VP start flat rostrally, approximately on the horizontal plane, but becomes oriented vertically as the axis curves under the temporal pole and reaches the underside of the temporal cortex.