(5) Inhibitory interneurons create temporal patterning of pyramidal cell activity resulting in odor-evoked cortical oscillations, which can enhance synchrony of afferent and intrinsic synaptic activity onto individual neurons as well as synchrony of coactive neurons. (6) Synaptic plasticity

is regulated by neuromodulatory inputs from the basal forebrain and brainstem. (7) Due to differences in local circuitry and top-down inputs, different subregions of the olfactory cortex may play different roles in odor coding, with more rostral regions dedicated to synthetic processing of odor object quality and increasingly complex associations (odor categories, learned hedonics, context, etc.) mediated PD173074 in vivo by more caudal regions. Below, we summarize new data within the context of this model. While experimental data supporting some aspects of the model have existed (Haberly, 2001), this review will emphasize exciting recent findings that both provide new detail and further

clarify our view of this important region. Previous data using small injections of horseradish peroxidase or similar strategies have supported the view of broad, nontopographic distribution of olfactory bulb input to the piriform cortex (Buonviso et al., 1991 and Ojima et al., 1984). More recent work c-Met inhibitor has explored this question in greater detail. Electroporation of tetramethylrhodamine (TMR)-dextran into identified glomeruli (Sosulski et al., 2011) or viral labeling of mitral/tufted cells from specific glomeruli (Ghosh et al., 2011) allowed tracing output projections to the cortex from Dipeptidyl peptidase individual glomeruli. Mitral and tufted cells from specific glomeruli projected throughout olfactory cortex, with no identifiable spatial pattern in the piriform cortex. Output from different glomeruli showed similar diffuse projections, providing ample opportunity

for convergence of input from different glomeruli onto individual target neurons. The broad anatomical distribution of fibers projecting from individual glomeruli to the piriform cortex is associated with a broad distribution pre-synaptic mitral/tufted cell activity following stimulation of individual glomeruli. Using transgenic mice expressing synaptopHluorin in mitral/tufted cells and either electrically stimulating individual glomeruli or delivering odor pulses revealed broad, overlapping patterns of presynaptic afferent activity in piriform cortex (Mitsui et al., 2011). This technique is particularly useful for such mapping because, as discussed elsewhere, spatial patterns of odor-evoked postsynaptic cortical activity will reflect both afferent and intrinsic fiber driven responses, and thus are not a good indicator of purely afferent input patterns. While the output of individual glomeruli is distributed across the piriform cortex, individual cortical neurons receive input from broadly distributed glomeruli, in a classic divergent-convergent pattern.