LETTER Communicated by Christof Koch Ion Channel Stochasticity May Be Critical in Determining the Reliability and Precision of Spike Timing

The ring reliability and precision of an isopotential membrane patch consisting of a realistically large number of ion channels is investigated using a stochastic Hodgkin-Huxley (HH) model. In sharp contrast to the deterministic HH model, the biophysically inspired stochastic model re-produces qualitatively the different reliability and precision character-istics of spike ring in response to DC and uctuating current input in neocortical neurons, as reported by Mainen & Sejnowski (1995). For DC inputs, spike timing is highly unreliable; the reliability and precision are signicantly increased for uctuating current input. This behavior is crit-ically determined by the relatively small number of excitable channels that are opened near threshold for spike ring rather than by the total number of channels that exist in the membrane patch. Channel uctu-ations, together with the inherent bistability in the HH equations, give rise to three additional experimentally observed phenomena: subthresh-old oscillations in the membrane voltage for DC input, “spontaneous