The ratio between synchronous and asynchronous release probability controls the optimal operating point of the synapse.

Mutual information rate (solid lines) and energy-normalized information rate (dashed lines) of the synapse are plotted as a function of input spike rate for different values of default (maximum) synchronous spike-evoked release probability, p0. (A) The default asynchronous release probability is fixed at q0 = 0.1. The black lines connect the maximum values of the curves. (B) The default asynchronous release probability is a fraction of the default synchronous spike-evoked release probability, q0 = p0/10. (C) Similar to (B) for q0 = p0/5. The other parameters of the model are L = 20, c = d = 0.5, and e = f = 0.1.