When somatic firing undermines dendritic compartmentalization

Abstract

Event Abstract Back to Event When somatic firing undermines dendritic compartmentalization Bardia F. Behabadi1* and Bartlett W. Mel1 1 University of Southern California, Department of Biomedical Engineering, United States Neocortical pyramidal neurons (PNs) exchange a dense plexus of interconnections, and most of these synapses are formed directly onto basal dendrites (BDs). Our working model describing the "arithmetic" of synaptic integration in these dendrites has been a 2-layer network (Archie & Mel, 2000; Poirazi et al. 2003; Polsky et al. 2004): the first layer consists of a set of separately thresholded dendritic subunits with sigmoidal input-output curves; the second layer calculates a sum of all the dendritic outflows reaching the soma, and then applies an F-I curve representing the cell’s axo-somatic spike-generating mechanism. A hallmark of 2-layer models is functional compartmentalization: within-branch summation is subject to an additional layer of (dendritic) nonlinearity in comparison to between-branch summation. In an augmentation to the basic 2-layer model, we recently found evidence in both models and experiments that flexible modulation of dendritic integration, including both threshold-lowering and gain-boosting effects, and combinations thereof, can be achieved by targeting modulatory synapses non-uniformly along the proximal-distal axis of a basal dendrite (Behabadi, Polsky, Schiller & Mel, SFN 2007). This novel mechanism for flexible modulation could allow interactions between distinct pathways (vertical, horizontal, callosal, etc.) impinging on PN basal dendrites to be tailored to the modulatory needs of the specific cortical circuit. Experiments in brain slices support the augmented 2-layer model, but so far only in the subthreshold range where responses are reported as somatic depolarization (Behabadi, Polsky, Sciller & Mel SFN 2007). It remains unknown what effect the axo-somatic spike-generating mechanism may exert on dendritic integration in PN basal dendrites, though modeling studies suggest the effects can be powerful, potentially overwhelming compartment-specific dendritic nonlinearities. In this work we separate the effects of location-dependent within-branch and between-branch interactions using further compartmental modeling studies. We find that the somatic spike-generating mechanism, when allowed to have a high threshold (as in typical slice conditions), exerts a global nonlinearity that does indeed occlude within-branch nonlinearities - thus undermining the compartmentalized functioning of the dendritic tree. However, when the axo-somatic nonlinearity is neutralized by biasing the soma to near it’s spike threshold using background synaptic inputs, a nearly pure location-dependent within-branch nonlinearity is revealed, while between-branch nonlinearities are virtually eliminated. Our findings lend further "moral" support to the augmented 2-layer model, and point to the unexpected role of low background firing rates in promoting compartmentalized dendritic processing. Conference: Computational and Systems Neuroscience 2010, Salt Lake City, UT, United States, 25 Feb - 2 Mar, 2010. Presentation Type: Poster Presentation Topic: Poster session III Citation: Behabadi BF and Mel BW (2010). When somatic firing undermines dendritic compartmentalization. Front. Neurosci. Conference Abstract: Computational and Systems Neuroscience 2010. doi: 10.3389/conf.fnins.2010.03.00115 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 22 Feb 2010; Published Online: 22 Feb 2010. * Correspondence: Bardia F Behabadi, University of Southern California, Department of Biomedical Engineering, Los Angeles, United States, behabadi@usc.edu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Bardia F Behabadi Bartlett W Mel Google Bardia F Behabadi Bartlett W Mel Google Scholar Bardia F Behabadi Bartlett W Mel PubMed Bardia F Behabadi Bartlett W Mel Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.