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A Brief History of Time (Constants)

Koch, Christof and Rapp, Moshe and Segev, Idan (1996) A Brief History of Time (Constants). Cerebral Cortex, 6 (2). pp. 93-101. ISSN 1047-3211. PMCID 8670642. http://resolver.caltech.edu/CaltechAUTHORS:20120208-103527408

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Abstract

That the cerebral cortex processes information at prodigious speeds cannot be doubted. Yet the passive time constant, τ_m of neurons, often thought of as a measure of the neuron's “response time” to synaptic input, is relatively long. In the 1950s, τ_m was estimated to be only a few milliseconds for mammalian central neurons; with improvement in recording techniques, its estimated value grew over the years and it now stands near 20–100 msec. However, as we will argue here, the functional meaning of τ_m is ambiguous. On the basis of a newly introduced definition of local delay, we show that the time window for synaptic integration in passive dendritic trees can be much smaller than the time constant. We argue that the voltage response to very brief synaptic inputs is essentially independent of τ_m. We discuss how τ_m can change dynamically with the global activity of the network, as well as the difficulties of defining a time constant in structures with voltage-dependent elements. We conclude that the classically defined τ_m only provides a very rough estimate, typically an overestimate, of the response time of neurons and that alternative measures are required to capture the dependency of the time course of the membrane potential on ligand-gated and/or voltage-dependent membrane conductances.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1093/cercor/6.2.93DOIArticle
http://cercor.oxfordjournals.org/content/6/2/93PublisherArticle
http://www.ncbi.nlm.nih.gov/pubmed/8670642PubMed Central IDPubMed Article
Additional Information:© 1996 Oxford University Press. We thank Ōjvind Bernander and Hagai Agmon-Snir for their detailed comments and their help in preparing the manuscript. The research reported here was funded by grants to C.K. from ONR and the NIMH Center for Neuroscience and by grants to I.S. from ONR and BSE I.S. acknowledges the hospitality of the Mathematical Research Branch (NIDDK) at the NTH in Bethesda, and C.K., the hospitality of the Santa Fe Institute in Santa Fe, New Mexico. Early versions of the manuscript were written while these two authors spent part of their summer at these institutions.
Group:Koch Laboratory, KLAB
Funders:
Funding AgencyGrant Number
Office of Naval Research (ONR)UNSPECIFIED
NIMH Center for NeuroscienceUNSPECIFIED
PubMed Central ID:8670642
Record Number:CaltechAUTHORS:20120208-103527408
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20120208-103527408
PubMed Central ID:8670642
Official Citation: Christof Koch, Moshe Rapp, and Idan Segev A Brief History of Time (Constants) Cereb. Cortex (1996) 6(2): 93-101 doi:10.1093/cercor/6.2.93
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:29195
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:08 Feb 2012 18:55
Last Modified:07 Oct 2013 17:53

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