Robustness to common perturbations in memory networks with negative-derivative feedback. The networks can maintain spatially localized, persistent activity robustly against either global (A–F) or local (G–L) perturbations that preserve the balance between excitation and inhibition such as changes in intrinsic gain (A–C, G–I) or changes in synaptic weights or loss of a fraction of the neurons in a given subpopulation (D–F, J–L). The local perturbations were in neurons whose preferred directions lie between 1/8π and 3/8 π, represented by the black bar along the x-axis. Activity profiles are shown for 3 s into the delay period.