  Recent studies of cortical neurons driven by fluctuating currents revealed
cutoff frequencies for action potential encoding of several hundred Hz.
Theoretical studies of biophysical neuron models have predicted a much lower
cutoff frequency of the order of average firing rate or the inverse membrane
time constant. The biophysical origin of the observed high cutoff frequencies
is thus not well understood. Here we introduce a neuron model with dynamical
action potential generation, in which the linear response can be analytically
calculated for uncorrelated synaptic noise. We find that the cutoff frequencies
increase to very large values when the time scale of action potential
initiation becomes short.
