Figure 2. Ca²⁺ increases in the stochastic model.

A, B, Ca²⁺ increase due to stimulation of PF and CF inputs with Δt = 160 msec (A) and Δt = −400 msec (B) in the stochastic model in a spine volume (gray lines, n = 2,000 for each timing, 20 examples are shown) and in a cell volume (black lines, n = 20 for each timing). C, Distributions of the Ca²⁺ response in a spine volume with Δt = 160 msec (solid line) and Δt = −400 msec (dashed line). Black and white arrowheads indicate the means of the Ca²⁺ response in a cell volume with Δt = 160 msec and Δt = −400 msec, respectively. Note that Ca²⁺ increases in a cell volume were almost the same between trials, leading to the overlap of the time courses (A, B). D, The distribution of the Ca²⁺ response (upper panel) was divided into the distribution with Ca²⁺ spikes (s = 1, black) and the distribution without Ca²⁺ spikes (s = 0, gray with dashed line). Then, each right (s = 1) and left (s = 0) distribution is decomposed into the probability components, which is probability of Ca²⁺ spiking (middle panel), and amplitude components, which is distribution of the Ca²⁺ response conditioned by Ca²⁺ spiking (lower panel). See materials and methods for the detailed descriptions.