FIG. 1.

Schematic representation of the subthreshold model part and interspike interval (ISI) distributions obtained with the renewal model. A: the subthreshold part of the model extends the electrical circuit analogy of Erchova et al. (2004) and Schreiber et al. (2004a). Specifically, the previously constant conductance of the middle parallel branch is now replaced by a time-dependent stochastic conductance to capture cell-intrinsic noise. As stated, the parameters γ, δ, R₀, and V_r can be expressed in terms of the circuit parameters. The parameter Q denotes the noise strength of conductance fluctuations: Q ∼ Np(1 − p)/τ, where N is the number of channels, p is the opening probability, and τ is the correlation time of conductance noise. For details, see Verechtchaguina et al. (2007). B: two cumulative ISI distributions obtained with the renewal model (in the Stratonovich approximation). The analytical curves are obtained for two parameter sets that differ in the subthreshold resonance frequency f_res and, consequently, also in the frequency of subthreshold membrane potential oscillations f_osc (top: f_osc = 10 Hz; bottom: f_osc = 5 Hz); see Eq. 4. The distance between the 1st and 2nd peaks of the ISI densities (insets) is equal to the period of subthreshold oscillations and thus also approximately equal to the inverse of the subthreshold resonance frequency.