  In a generic neuron model, we present the linear response theory for the
firing rate in response to both time dependent input currents and noise
amplitudes. In both cases the signal transmission is strongly attenuated for
frequencies above the stationary firing rate. For high frequencies both the
mean input and the noise transmission function decay as \omega^{-2},
independent of model details. Our results indicate that previously suggested
mechanisms for near instantaneous transmission of information are not
consistent with the spike generation mechanism of real neurons.
