Figure 5.

Coefficient of variation R_T vs noise amplitude σ_l of layer l in isolation. In (A) and (B), we have the R_T curves of weak and strong chemical synaptic strengths κ_l,c, respectively, for short, intermediate and long synaptic time delays τ_l,c. In (C) and (D), we have the R_T curves of short and relatively long synaptic time delays τ_l,c, respectively, for weak, intermediate and strong synaptic strengths κ_l,c. Increasing (decreasing) the inhibitory chemical synaptic strength κ_l,c deteriorates (enhances) SISR by increasing (decreasing) the values of R_T and by shrinking (extending) the interval of the noise amplitude in which R_T can achieve very low values. Thus, inhibitory chemical synaptic strength qualitatively behaves as the electrical synaptic strength in optimizing SISR. However, electrical synaptic and inhibitory chemical synaptic time delays show opposite behaviors in the enhancement of SISR. Decreasing (increasing) the length of inhibitory chemical time delays τ_l,c, deteriorates (enhances) SISR by increasing (decreasing) the values of R_T and by shrinking (extending) the interval of the noise amplitude in which R_T can achieve very low values. This effect is particularly pronounced when the chemical synaptic strength is strong. For example, in (C), for κ_l,c = 1.0 and τ_l,e = 1.0, the red R_T-curve achieves relatively high minimum value R_Tmin = 0.71 occurring at a relatively large noise amplitude ${\sigma }_l=4.6\times 10^{-4}$, indicating a very poor SISR. Parameters for layer l are: N = 25, n_l,c = 8, β = 0.75, ε = 0.0005, α = 0.5.