Stochastic Ion Channel Gating in Dendritic Neurons: Morphology Dependence and Probabilistic Synaptic Activation of Dendritic Spikes
(A–B) Examples of membrane currents (top), membrane potential (middle) and corresponding power spectra from 100 s of simulated activity (bottom), for models containing passive leak Na+ and K+ channels with slow (A) or fast (B) kinetics. The power spectra are shown for simulations with time steps of 10 µs (solid traces), 100 µs and 1000 µs (light traces). The voltage-clamp simulations are of a single isopotential compartment containing 201 Na+ and 1407 K+ leak channels. The current-clamp simulations are for a cable of length 1000 µm and radius 1 µm, containing 8050 channels distributed across 237 compartments. (C) The error in the mean and variance of a simulated current, mediated by 50 Na+ channels clamped at −20 mV for 100 s of simulated time, is plotted as a function of the simulation time step. (D) Power spectra for the currents in (C). Long time steps fail to simulate high frequency current fluctuations and introduce aliasing effects at low frequencies. (E–F) The computation time per simulation time step, required by NEURON (closed symbols) or PSICS (open symbols) for simulations as in (C–D), is plotted as a function of the duration of the simulation time step (E), or as a function of the number of simulated channels when the time step is 20 µs (F). (G) The computation time per simulation time step, required by NEURON or PSICS for simulations as in Figure 3F, is plotted as a function of the duration of the simulation time-step. Simulation times are for a cable divided into either 101 compartments (triangles) or 1001 compartments (circles).