Piriform Cortex and Amygdala

Publisher Summary A ventral view of the cerebral hemispheres of mammals shows an array of structures ultimately connected with the olfactory bulbs through the olfactory tracts. This is the basis for the old concept of rhinencephalon, a series of neural centers in the cerebral hemispheres, located ventral to the rhinal fissure, for which an olfactory role was assumed. Although mice lack a conspicuous rhinal fissure, their “rhinencephalon” is well developed. The concept of the rhinencephalon is difficult to sustain nowadays, as it includes neural centers of diverse origin, organization and nature. The rhinencephalon comprises several allocortical areas that constitute the olfactory cortex, deep to these areas there are always non-layered cell groups, some of which are targeted by afferents from non-olfactory cortical and extra-telencephalic centers. These hypopallial nuclei are more developed in the caudal cerebral hemispheres where, together with portions of the overlying olfactory cortex, they configure the pallial portion of the amygdala. At these caudal levels, the subpallium shows a complex organization and receives its main input from the pallial amygdala. This chapter reviews the structure, neurochemistry, and connections of these structures in the mouse brain of the caudal subpallium are frequently grouped under the term “extended amygdale.” A portion of the extended amygdala also receives olfactory inputs, whereas the other division, the central extended amygdala, has no direct links with the olfactory system. The fiber connections of the Piriform cortex have been studied in detail in the rat. A number of tracing experiments in the lab, as well as available data in the literature, indicate that the olfactory cortex of the mouse shows a pattern of connections virtually identical to that of rats.