  The optimal patterns of synaptic conductances for spike generation in central
neurons is a subject of considerable interest. Ideally, such conductance time
courses should be extracted from membrane potential (Vm) activity, but this is
difficult because the nonlinear contribution of conductances to the Vm renders
their estimation from the membrane equation extremely sensitive. We outline
here a solution to this problem based on a discretization of the time axis.
This procedure can extract the time course of excitatory and inhibitory
conductances solely from the analysis of Vm activity. We test this method by
calculating spike-triggered averages of synaptic conductances using numerical
simulations of the integrate-and-fire model subject to colored conductance
noise. The procedure was also tested successfully in biological cortical
neurons using conductance noise injected with dynamic-clamp. This method should
allow the extraction of synaptic conductances from Vm recordings in vivo.
