Figure 5.
Dynamic range increases with synaptic variance. Data are results of dynamic-clamp experiments run using the deterministic (solid symbols) and stochastic (open symbols) models of neurotransmitter release, with model parameters held constant, except for the number of release sites (NS). As NS increased, the conductance variability decreased. A–C, Spike probability for each pulse (Pspike) as a function of the pulse's average synaptic conductance (GAMPA) in a representative experiment. For the deterministic model (solid symbols), dynamic range was uniformly narrow. For the stochastic model, the dynamic range was greater for low NS. Dynamic ranges for the different conditions are indicated using the dumbbells above each plot. D, Dynamic range as a function of NS for five experiments. Dynamic range was widest for the smallest number of release sites and narrowed with increasing NS. Dynamic range was most narrow with the deterministic model. E, Dynamic range as a function of synaptic variance. Dynamic ranges from D are plotted against the CV of the steady-state synaptic conductances for different NS (mean ± SEM of five experiments).