Figure 1.

(a) Schematic of network structure illustrating synaptic interactions from inhibitory cells (red) with fixed synaptic weight w_I and from excitatory cells (blue) with varied synaptic weight w_E. Lightning bolts represent the external noisy stimuli with average frequency 40 Hz applied to each neuron in the network. (b) Relationship between E/I ratio values and E-I current difference (total current) values in asymptotic balance states as excitatory synaptic weight w_E was monotonically increased (arrows show direction of relative change with increasing w_E). Four trajectory curves correspond to 4 values of inhibitory synaptic weight w_I (given in legend in mS/cm2). Inset in panel b shows a close-up of the asymptotic E=I balanced state (i.e. when E/I ratio is near 1 and total current is near 0) with two trajectories (violet and yellow) that crossed this balanced state 3 times. (c) Trajectory curves of E/I ratio values and network spiking activity values (in Hz computed during the 1.5s simulation in the asymptotic balance state), as excitatory synaptic weight w_E was systematically increased for the 4 values of w_I (arrows show direction of change with increasing w_E). For two trajectories (violet and yellow) although the E/I ratio oscillated above and below 1, spiking rates continued to increase as w_E was increased.