Architecture of the lateral olfactory cortex

The caudolateral part of AON is continuous through transitional zones with the piriform cortex, which in turn gives way caudally to periamygdaloid and transition cortices and then the lateral entorhinal cortex. Collectively, these cortical structures comprise the entire temporal cortical mantle ventral to the rhinal sulcus. 

Piriform cortex (Fig. 15 C-D 17 A-F), also referred to as pyriform or prepyriform cortex, is a phylogenetically old, paleocortical structure. PC is located along the entire length of the lateral olfactory tract at the ventrolateral convexity of the base of the cortex. PC is thicker and more elaborate caudally than it is rostrally. PC is allocortical, having only two-three cellular layers and is thinner and less complex than the neocortex which has six layers. Haberly and Price (1978b) divided the piriform cortex into 3 layers that are further subdivided on the basis of cytoarchitecture and afferent connections. 

Layer I, the molecular layer, is the most superficial layer of PC. This layer is densely synaptic. The superficial half of this layer (la) contains the axons and synaptic terminals of mitral/tufted cells. The deep half (Ib) contains axons and terminals from ipsi- and contralateral olfactory cortical association inputs. Layer II is a distinct, narrow, tightly packed cell layer containing pyramidal neurons whose apical dendrites extend into layer 

Some smaller cells in layer Ila lack basal dendrites (Haberly and Price, 1978b) and are reminiscent of dentate granule cells in the hippocampus. Layer III is a thicker but less densely packed cellular layer containing larger pyramidal cells whose dendrites also extend throughout layer I. Layer III also contains large multipolar cells whose dendrites do not enter layer I and other intrinsic neuronal types. Layer III exhibits a superficial 

PC also contains numerous interneurons. The distribution of GABAergic interneurons has been described for the opossum and appears to be quite similar in the rat (Haberly, personal communication). These cells are found in all layers of piriform cortex (Fig. 25), including layer I, where they may function as a feedforward inhibitory system. There have been numerous reports of neuropeptide containing neurons in olfactory cortex many of these have a morphology consistent with an interneuron, but little is known about their connections or functions. 

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