Diverse Patterns of Odor Representation by Neurons in the Anterior Piriform Cortex of Awake Mice

Abstract

The mammalian piriform cortex receives direct synaptic input from the olfactory bulb and is likely the locus for the formation of odor percept. It remains unclear how individual cortical neurons encode olfactory information in unanesthetized animals. By single-cell recordings from head-restrained awake mice, we studied the odor response profiles of individual neurons in the anterior piriform cortex (aPCX). Neurons were juxtacellularly labeled, and their cell types were determined by their morphology and neurotransmitter phenotypes. We found a considerable level of variability in selectivity patterns among pyramidal neurons (PNs). Approximately one-quarter of PNs were broadly activated by structurally dissimilar odorants, whereas the excitations to the rest of PNs were highly selective. Broad inhibition was only observed from a subpopulation of PNs. GABAergic neurons displayed nonselective excitatory responses to test odorants and rarely exhibited inhibition. In contrast, non-GABAergic nonpyramidal neurons in the deep layer tended to be strongly inhibited by multiple different odorants. Our findings suggest that odor representation is accomplished by both broadly tuned and narrow-tuned PNs in the aPCX of awake animals. In addition, various types of interneurons may play different roles in the intracortical processing of olfactory information.

Balanced feedforward inhibition and dominant recurrent inhibition in olfactory cortex

“…Consistent with this idea, disinhibition of the piriform cortex leads to epileptic activity (46)(47)(48)(49). All together, these feedforward and recurrent circuit features likely promote sparse responses (50)(51)(52)(53)(54) and low correlations (8,11,51) during odor processing.…”

Optogenetic Activation of Basal Forebrain Cholinergic Neurons Modulates Neuronal Excitability and Sensory Responses in the Main Olfactory Bulb

“…Neurons were tested with up to 16 odorants, each of which was delivered for five consecutive trials. The duration of odor application for each trial was 2 s with a 23 s intertrial interval to reduce habituation (Wilson, 1998;Zhan and Luo, 2010). An additional stream (100 ml/min) of pure air was injected into the airflow circuit for 3 s after the termination of a trial to minimize residual odorants from the previous trial.…”

Microcircuits Mediating Feedforward and Feedback Synaptic Inhibition in the Piriform Cortex

“…Because of its comparatively simple anatomy, together with the fact that its afferent inputs (i.e., the outputs of the bulb) are increasingly well understood, the PC has attracted attention as a model system for the study of cortical sensory processing (Neville and Haberly, 2004;Isaacson, 2005, 2006;Bekkers, 2006, 2011;Barnes et al, 2008;Luna and Schoppa, 2008;Bathellier et al, 2009;Johenning et al, 2009;Poo and Isaacson, 2009;Stettler and Axel, 2009;Stokes and Isaacson, 2010;Wilson, 2010;Davison and Ehlers, 2011;Franks et al, 2011;Poo and Isaacson, 2011;Wiegand et al, 2011). In particular, synaptic inhibition in the PC is of interest because of its likely relevance to olfactory coding and oscillations (Wilson and Bower, 1992;Kay et al, 2009;Isaacson, 2009, 2011;Kay and Beshel, 2010;Zhan and Luo, 2010;Manabe et al, 2011;Zelano et al, 2011).…”