Figure 5.

Simulating synaptic size dynamics as a stochastic Kesten process. A, Sizes of 1922 synapses were initialized using the experimental data of Figure 4F (t = 24) and evolved as stochastic Kesten processes for 320 steps using values of <ϵ> (and <η>) obtained in control networks (4J). Simulation parameters are indicated at bottom. Synaptic sizes at the last simulation step were plotted against their sizes 24 steps beforehand. Dashed line is a linear regression fit, whose parameters and coefficient of determination (R²) are indicated (top). B, Same data as in A, plotted as size change in last 24 steps as a function of synaptic size 24 h beforehand. Dashed line is a linear regression fit. C, Synaptic size distributions along the simulation. Dashed line is the experimentally measured distribution of normalized PSD-95 fluorescence of 1922 tracked synapses. Note the stability of this distribution over the duration of the simulation. D–F, Same as A–C but for 2032 synapses in chronically silenced networks using the experimentally derived values of <ϵ> (and <η>) obtained in silenced networks (Fig. 4J). G–I, Magnitude of synaptic size fluctuations in the simulated data using <ϵ> and <η> values derived from silenced and control networks. Averages of SDs, coefficients of variation and range/mean values calculated for all synapses over the last 24 simulation steps. Indicated p values are for t tests assuming unequal variances. J, Rates of synaptic elimination during simulations, that is, synapses whose sizes momentarily reached a value of zero and were thereafter removed. K, Convergence rates to stable (limiting) distributions. Four thousand synapses were initialized to a uniform value of 0.1 and evolved for 480 steps using values of <ε> (and <η>) obtained in control networks. L, Same as K using <ε> (and <η>) values obtained in chronically silenced networks. Note the slower convergence to the limiting distribution compared with K. M, Synaptic elimination during the simulations of K and L.