Pyramidal Cells in Piriform Cortex Receive Convergent Input from Distinct Olfactory Bulb Glomeruli

Abstract

Pyramidal cells in piriform cortex integrate sensory information from multiple olfactory bulb mitral and tufted (M/T) cells. However, whether M/T cells belonging to different olfactory bulb glomeruli converge onto individual cortical cells is unclear. Here we use calcium imaging in an olfactory bulb-cortex slice preparation to provide direct evidence that neurons in piriform cortex receive convergent synaptic input from different glomeruli. We show that the combined activity of distinct glomerular pathways recruits ensembles of pyramidal cells that are not activated by the individual pathways alone. This cooperative recruitment of cortical neurons only occurs over a narrow time window and is a feature intrinsic to the olfactory cortex that can be explained by the integration of converging, subthreshold synaptic input. Cooperative recruitment enhances the differences between cortical representations of partially overlapping input patterns and may contribute to the initial steps of olfactory discrimination.

The Olfactory System

“…In slices, focal activation of a single glomerulus was found to activate disperse layer II-III Pir neurons. Similar to Pir odor responses, stimulation of different glomeruli activated sparse but distinct ensembles in overlapping cortical areas with ∼10% of neurons responding to two glomeruli (Apicella et al, 2010). Simultaneously, stimulation of two glomeruli activated twice as many cells than the sum activated by either pathway alone.…”

Olfactory networks: from sensation to perception

“…First, 20-40% of piriform pyramidal cells that respond to an odor mixture fail to respond to the individual components of the same mixture [34 ]. Second, simultaneous stimulation of multiple glomerular sites is sufficient to increase activity in many pyramidal neurons distributed throughout piriform cortex, though these cells are not activated by stimulation of individual glomeruli [38,39]. Together, these results argue for a cooperative recruitment of pyramidal neurons when odor mixtures are presented.…”

Construction of functional neuronal circuitry in the olfactory bulb

“…This means that overall topography in the OB is not preserved in many areas of the olfactory cortex including piriform cortex. Transsynaptic retrograde tracing and functional mapping demonstrated that piriform neurons receive convergent inputs from multiple glomeruli [26,66,80,81]. In addition, 2-photon calcium imaging of piriform cortex failed to find any topographic representation of odors [82].…”