Metabolic cost of the network activity.

A-C: Cost at resting state (λ_ext = 0). A: Cost of the excitatory synaptic currents from the background input (Eq 35) and excitatory action potentials evoked by the background input. B: Cost of the action potentials (both excitatory and inhibitory) evoked by the background input. C: Total resting cost obtained by summing A and B. D: The total cost of the network activity is plotted against the output of the network (the total post-synaptic firing rate). Filled areas represent individual contributions of each cost component: cost of action potentials from the external population, cost of the excitatory synaptic currents, and cost of the post-synaptic (evoked) action potentials. As P_ext increases, the contribution of external action potentials to the overall cost decreases. With increasing a_rec, the contribution of excitatory synaptic currents increases. E: The cost of increasing the mean input by one action potential (w_AP, Eq 19) is significantly lower for higher P_ext. However, although the difference between P_ext = 0.01 and P_ext = 0.2 is approximately 10-fold, the difference between P_ext = 0.2 and P_ext = 1 is only approximately 2-fold, as the cost of the external population starts to contribute less to the overall cost.