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

Center for Neural Circuits and Behavior, Neuroscience Department, School of Medicine, Neurobiology Section, Division of Biology, and Howard Hughes Medical Institute, University of California, San Diego, La Jolla, California 92093-0634, USA.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.75). 10/2010; 30(42):14255-60. DOI: 10.1523/JNEUROSCI.2747-10.2010
Source: PubMed

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.

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Available from: Alfonso junior Apicella, Aug 14, 2015
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    • "For example, individual mitral cells project broadly throughout piriform cortex (Mitsui et al., 2011), and neighboring piriform cortical neurons can show completely different odor tuning and temporal entrainment to the respiratory cycle (Rennaker et al., 2007). Odor responses of piriform cortical neurons reflect both the combinatorial nature of their olfactory bulb afferent input (Apicella et al., 2010) as well as the nature of their intracortical association fiber input (Franks et al., 2011; Poo and Isaacson, 2011), which is also highly distributed and nontopographic (Haberly, 2001; Johnson et al., 2000). "
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    • "These results show that spatially segregated channels of odor information become integrated in the PC (or the MB). In brain slice experiments, investigators found that coincident inputs from multiple M/T cells are required to activate PC neurons (Apicella et al. 2010). Measuring the response of the PC population to odor mixtures revealed interactions between odors, exhibiting crossodor suppression as well as supralinear excitation (Stettler & Axel 2009, Wilson & Sullivan 2011, Yoshida & Mori 2007). "
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    ABSTRACT: Howis sensory information represented in the brain?Along-standing debate in neural coding is whether and how timing of spikes conveys information to downstream neurons. Although we know that neurons in the olfactory bulb (OB) exhibit rich temporal dynamics, the functional relevance of temporal coding remains hotly debated. Recent recording experiments in awake behaving animals have elucidated highly organized temporal structures of activity in the OB. In addition, the analysis of neural circuits in the piriform cortex (PC) demonstrated the importance of not only OB afferent inputs but also intrinsicPCneural circuits in shaping odor responses. Furthermore, new experiments involving stimulation of the OB with specific temporal patterns allowed for testing the relevance of temporal codes. Together, these studies suggest that the relative timing of neuronal activity in the OB conveys odor information and that neural circuits in the PC possess various mechanisms to decode temporal patterns of OB input. Expected final online publication date for the Annual Review of Neuroscience Volume 37 is July 08, 2014. Please see for revised estimates.
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    • "This relative timing provides a simple means to represent odorant concentrations with the reference time built into the signal. Since coincident timing of OB output to piriform cortex has been shown to determine the firing probability of pyramidal neurons in the cortex, variation in the MLTD could provide a high dynamic time window for integration in these neurons (Apicella et al., 2010). Thus, we propose that a coincident timing-based mechanism within the cortex, based upon MLTDs, could be used to represent odorant concentration in the olfactory cortex (Figure 4C). "
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    ABSTRACT: In mammals, each olfactory bulb (OB) contains a pair of mirror-symmetric glomerular maps organized to reflect odorant receptor identity. The functional implication of maintaining these symmetric medial-lateral maps within each OB remains unclear. Here, using in vivo multielectrode recordings to simultaneously detect odorant-induced activity across the entire OB, we reveal a timing difference in the odorant-evoked onset latencies between the medial and lateral halves. Interestingly, the latencies in the medial and lateral OB decreased at different rates as odorant concentration increased, causing the timing difference between them to also diminish. As a result, output neurons in the medial and lateral OB fired with greater synchrony at higher odorant concentrations. Thus, we propose that temporal differences in activity between the medial and lateral OB can dynamically code odorant concentration, which is subsequently decoded in the olfactory cortex through the integration of synchronous action potentials.
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