Parallel processing by distinct classes of principal neurons in the olfactory cortex

Understanding how distinct neuron types in a neural circuit process and
propagate information is essential for understanding what the circuit does
and how it does it. The olfactory (piriform, PCx) cortex contains two main
types of principal neurons, semilunar (SL) and pyramidal (PYR) cells. SLs
and PYRs have distinct morphologies, local connectivity, biophysical
properties, and downstream projection targets. Odor processing in PCx is
thought to occur in two sequential stages. First, SLs receive and
integrate olfactory bulb input and then PYRs receive, transform, and
transmit SL input. To test this model, we recorded from populations of
optogenetically identified SLs and PYRs in awake, head-fixed mice.
Notably, silencing SLs did not alter PYR odor responses, and SLs and PYRs
exhibited differences in odor tuning properties and response
discriminability that were consistent with their distinct embeddings
within a sensory-associative cortex. Our results therefore suggest that
SLs and PYRs form parallel channels for differentially processing odor
information in and through PCx.