Layer II contains the somata of superficial pyramidal cells, with apical

dendrites extending into Layer I and basal dendrites into Layer III. Layer IIa, a thin, superficial component of Layer II contains the somata of the pyramidal cell-like semilunar cells. These cells lack basal dendrites and appear to preferentially receive input from mitral/tufted cells, with relatively less input from association fibers (Suzuki and Bekkers, 2011). Unlike other pyramidal cells, they do not project back to the olfactory bulb. Layer III contains the somata of deep pyramidal cells, as well as a variety of interneurons. At least five classes of piriform cortical GABAergic interneurons have been identified (Suzuki and Bekkers, 2010a and Young and Sun, 2009). Deep to layer III lies the endopiriform nucleus. Whether the endopiriform nucleus should be considered piriform cortical DNA Damage inhibitor layer IV is unclear, though the two structures are highly interconnected. Protein Tyrosine Kinase inhibitor The endopiriform nucleus contains dense local and extended excitatory interconnections with relatively low levels of GABAergic interneurons (Behan and Haberly, 1999 and Ekstrand et al., 2001). This combination of autoexcitation and low

inhibition makes the endopiriform highly susceptible to seizure development (Behan and Haberly, 1999). It sends strong, dispersed output throughout the piriform cortex and other perirhinal structures. These characteristics have led to the hypothesis (Behan and Haberly, 1999) that the endopiriform nucleus may be involved in generating sharp-waves in olfactory cortex similar to those described in the hippocampal formation (Buzsáki, 1986) and that these sharp-waves may contribute to plasticity and odor memory. In fact as described below, sharp-waves have recently been described in piriform cortex (Manabe et al., 2011). Understanding the role of olfactory cortex in odor perception has been the focus of a variety of theoretical and computational models (Ambros-Ingerson et al., 1990,

Granger and Lynch, much 1991, Haberly, 1985, Haberly, 2001, Haberly and Bower, 1989, Hasselmo et al., 1990 and Linster et al., 2009). An underlying theme of many of these is olfactory cortex as autoassociative combinatorial array, capable of content addressable memory. Here, we use this model as an organizing framework to describe recent advances in understand olfactory cortical structure and function. The basic model describes the olfactory cortex in terms of a combinatorial, autoassociative array capable of content addressable memory (Haberly, 2001). Put simply, the model proposes that unique combinations of odorant features, encoded in the spatiotemporal pattern of olfactory bub glomerular output, can be synthesized, stored and recalled in the activity of distributed ensembles of olfactory cortical pyramidal cells (Figure 2).