Fig. 6

Maximum stability of memory states, for a given neural firing-rate curve, is alwaysgreater when synapses are facilitating rather than static. a–b Lowthreshold, ${\beta }_2=0.451$. c–d Medium threshold,${\beta }_2=0.701$. e–f High threshold,${\beta }_2=0.951$. a, c, e Synapses are static.b, d, f Synapses are facilitating. All panels:Steepness of single neuron firing-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. Darkblue: no bistability exists. Light blue = low stability;orange-red = high stability; cyan-green boundary = optimallifetime of one hour