Fig. 7

A hybrid model demonstrates the reduction in lifetime attributable to the enhancedfluctuations in postsynaptic conductance produced by synaptic facilitation.a–b Low threshold, ${\beta }_2=0.451$. c–d Medium threshold,${\beta }_2=0.701$. e–f High threshold,${\beta }_2=0.951$. a, c, e Lifetime of states in thehybrid model with synaptic facilitation but with the noise due to static synapses.Dark blue: no bistability exists. Light blue = low stability;orange-red = high stability; cyan-green boundary = optimallifetime of one hour. b, d, f Logarithm of the ratio ofFigs. 7a, 7c, 7e to 6b, 6d, 6f, respectively, demonstrates the decrease in state lifetime attributableto enhanced noise when synapses are facilitating. Dark blue: ratio = 1.Cyan-yellow, ratio >e. Orange-light red, ratio$>e^2$. Dark red, ratio $>e^3$. All panels: Steepness of single neuronfiring-rate curves increase with ${\beta }_1$ (y-axis) while maximum curvature increases with${\beta }_3$ (x-axis). Stability of a bistable system isdetermined by the minimum lifetime of either of the two activity states. Maximumstability is calculated for each firing-rate curve as a function of connectionstrength and plotted after logarithmic scaling in color code