Koch, Christof and Douglas, Rodney and Wehmeier, Udo (1990) Visibility of synaptically induced conductance changes: theory and simulations of anatomically characterized cortical pyramidal cells. Journal of Neuroscience, 10 (6). pp. 1728-1744. ISSN 0270-6474. http://resolver.caltech.edu/CaltechAUTHORS:20130816-103205557
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A recent report has provided evidence that there are no significant increases in the neuronal input conductance during the response of cortical cells in cat visual cortex to non-preferred visual stimuli (Douglas et al., 1988). A criticism of experiments of this kind is that changes in the membrane conductance occurring in the dendritic tree may not be visible from electrodes that impale the soma. Our paper describes theoretical and numerical results concerning the visibility of synaptically induced conductance changes from intracellular electrodes, in both ideal and anatomically well-characterized cortical neurons. Based on earlier work by Rall (1967), we here derive theoretical expressions for the change in input conductance at any location in a passive dendritic tree resulting from activation of a single synapse and obtain bounds for the effects of multiple synapses. We find that the conductance change measured at the cell body is always less than the sum of the synaptic conductance changes and that this observed conductance change does not depend on the synaptic reversal potential. For the case of an infinite dendritic cylinder, the change in input resistance due to a single synaptic input decays exponentially with distance of the synapse from the recording site. Numerical simulations of synaptic inputs that change approximately as fast as the membrane time-constant produce an increase in input conductance that is only slightly less visible than that of a constant input. We also compute the changes in somatic input conductance of 2 morphologically identified pyramidal cells from cat visual cortex during activity of a single inhibitory basket cell with known synaptic input locations. We find that the increase in conductance due to the activity of the inhibitory basket cells is clearly visible from the cell body of the pyramidal cells and that a 70% reduction in the amplitude of excitation is associated with at least a 30% increase in somatic input conductance, which would be visible in intracellular recordings. Taken together with the negative experimental evidence of Douglas et al. (1988), our results cast doubt on a large class of models of direction selectivity that rely on synaptically mediated inhibitory conductance increases to veto or block excitatory conductances increases.
|Additional Information:||© 1990 by Society for Neuroscience. Received July 10, 1989; revised Oct. 16, 1989; accepted Nov. 28, 1989. We thank John Anderson for his devotion to histology, and Ferenc Mechler for writing some of the programs. We also thank Kevan Martin and David Ferster for detailed comments. Our collaboration was made possible by a Bioscience Grant for International Joint Research from the New Energy and Industrial Technology Development Organization in Japan. C.K. is supported by grants from the Air Force Office of Scientific Research, the James S. McDonnell Foundation, and a Presidential Young Investigator Award from the National Science Foundation. R.J.D. acknowledges the support of the Medical Research Council of the United Kingdom, the Medical Research Council of South Africa, and the University of Cape Town.|
|Group:||Koch Laboratory, KLAB|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||KLAB Import|
|Deposited On:||08 Feb 2008 07:57|
|Last Modified:||29 Apr 2014 18:37|
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