Fig. 6.

Sagittal view of the basic organization of the ancestral vertebrate brain. Here, the neural tube is color-coded according to its major subdivisions: prosencephalon, dimesencephalon, rhombencephalon, and spinal cord. The alar portion of the second segment of the prosencephalon (PHy) expands into the telencephalon, in which additional domains can now be distinguished. These include subpallial sectors (striatum and pallidum) and pallial sectors (ventrolateral and medial). The putative future site of the dorsal pallium is marked as a subregion of the ventrolateral pallium. Only a few of the major pathways are shown, emphasizing how visual and olfactory information (blue lines, in online color figure) is used to guide tectal approach and avoidance behaviors (purple lines), and telencephalic foraging behaviors (green lines), arbitrated by modulatory pathways from the subpallium (red dotted lines). OB, olfactory bulb; PHy, peduncular hypothalamus; SNr, substantia nigra reticulata; THy, terminal hypothalamus