A method to estimate synaptic conductances from membrane potential fluctuations.
Michael Rudolph, Zuzanna Piwkowska, Mathilde Badoual, Thierry Bal and Alain Destexhe

Journal of Neurophysiology 91: 2884-2896, 2004.

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In neocortical neurons, network activity can activate a large number of synaptic inputs, resulting in highly irregular subthreshold membrane potential (Vm) fluctuations, commonly called “synaptic noise”. This activity contains information about the underlying network dynamics, but it is not easy to extract network properties from such complex and irregular activity. Here, we propose a method to estimate properties of network activity from intracellular recordings and test this method using theoretical and experimental approaches. The method is based on the analytic expression of the subthreshold Vm distribution at steady-state in conductance-based models. Fitting this analytic expression to Vm distributions obtained from intracellular recordings provides estimates of the mean and variance of excitatory and inhibitory conductances. We test the accuracy of these estimates against computational models of increasing complexity. We also test the method using dynamic-clamp recordings of neocortical neurons in vitro. By using an on-line analysis procedure, we show that the measured conductances from spontaneous network activity can be used to recreate artificial states equivalent to real network activity. This approach should be applicable to intracellular recordings during different network states in vivo, providing a characterization of the global properties of synaptic conductances and possible insight on the underlying network mechanisms.
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An Editorial focus has been written about this article:

A. Korngreen, Noise in the foreground. Journal of Neurophysiology 91: 2400, 2004.

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