Odor Coding by Distinct Classes of Principal Neurons in Piriform Cortex

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Understanding the roles that distinct neuron types play within a neural circuit will provide important mechanistic insight into understanding what the circuit does and how it does it. Piriform cortex (PCx) is the largest cortical recipient of odor information from the olfactory bulb (OB). It is thought to be the locus of odor perception and has been linked to several other crucial olfactory processing functions. However, the circuit mechanisms by which many of these ascribed functions occur as well as a comprehensive description of the role of PCx in olfaction remain unclear. PCx contains several different types of excitatory principal neurons. The two main types are semilunar cells (SL) and superficial pyramidal cells (PYR). SLs and PYRs have distinct morphologies, local connectivity, biophysical properties, and downstream projection targets, signifying potentially different roles in odor processing. An incisive study of if and how SLs and PYRs differentially encode odors will advance our understanding of PCx function and olfactory processing, as a whole.Odor processing in PCx has been hypothesized to occur in two sequential stages. First, SLs receive and integrate afferent OB inputs and then PYRs receive, transform, and transmit SL inputs to downstream regions. To probe if and how these two cell types differentially process odor information, I recorded from populations of optogenetically identified SLs and PYRs in awake, head-fixed mice. I then characterized their odor response properties, and selectively manipulated SL activity while mice were passively smelling odors and performing an odor-driven behavior. I found that SLs and PYRs received sensory information from the OB directly and simultaneously, and PYRs did not rely on SL activity to respond to odors, suggesting that these two cell types form parallel channels for processing odor information. Additionally, SLs and PYRs exhibited differences in odor response properties that were consistent with their distinct local connectivity, suggesting that distinct cell types differentially transform odor information. Finally, SLs and PYRs have distinct roles in mediating odor-driven behaviors. Together, my data show that SLs and PYRs form parallel channels for differentially processing odor information in and through PCx. More broadly, my findings provide evidence that PCx contains a functionally diverse population of neurons. Registering specific PCx functions to specific neuron types or subpopulations of neurons will provide a framework for determining what it is that PCx does for olfaction and how it does it.






Nagappan, Shivathmihai (2022). Odor Coding by Distinct Classes of Principal Neurons in Piriform Cortex. Dissertation, Duke University. Retrieved from https://hdl.handle.net/10161/25170.


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