Figure 2. The behavior of the stochastic granule cell model in response to three different depolarizing current pulses.

In each trace, firing is simulated for 0.4 seconds with a time step of 10⁻⁵ seconds. In the upper panel the depolarizing current is below firing threshold (I_app = 11 pA) and in the middle panel just above firing threshold (I_app = 12 pA). In the lower panel, the depolarizing current is considerably larger (I_app = 29 pA). The upper trace illustrates the spontaneous firing occasionally present when a depolarizing current below firing threshold is given. The middle trace shows the irregularity in firing with small depolarizing current pulses. The two uppermost traces also contain random subthreshold oscillations. With larger depolarizing current pulses, firing becomes more regular, as shown in the lower panel. Due to stochastic nature of the model, the interspike intervals and the height of action potentials also show slight irregularity. In each case σ = 0.5 and all other parameters are fixed as explained in the text.