a, Membrane potential V_i(t) time series segment for a few cells from a N = 500-cell network simulation with connectivity 0.2 under fixed excitation. Each cell is in a different panel. Note the different y-axes scales of the top two panels. b, Time series of postsynaptically bound transmitter quantity g_i(t) corresponding to a, including the same cells. This is a low-pass filter of presynaptic firing rate. Each cell time series is in a different color corresponding to a.