Dynamic feedback inhibition.

<p><b>A.</b> Example statistics of inhibitory vs. excitatory currents to three example neurons during a recall trial. Blue: neuron correctly recalling a bit in the originally stored pattern, correctly recalled; red: neuron correctly recalling a bit in the originally stored pattern; gray: neuron with high variability during the trial, corresponding to an incorrectly recalled bit. Individual dots correspond to different time steps within the same recall trial. <b>B.</b> Effect of replacing feedback inhibition by tonic inhibition with the same average level. <b>C.</b> Evolution of the mean population activity during retrieval when network dynamics involve feedback (red) versus tonic inhibition (blue). Lines correspond to different trials. <b>D.</b> Schematic view of inhibitory connectivity in the network. Pyramidal neurons sending or receiving monosynaptic excitation (disynaptic inhibition) to example neuron 2 (black) are colored red (blue). Blue circle: local interneuron (not explicitly modeled) mediating disynaptic lateral inhibition received by neuron 2. E/I overlap is measured as the ratio of presynaptic pyramidal neurons colored both blue and red, 0% is chance. <b>E.</b> Total somatic current (through recurrents) to an example cell in a sparsely connected network (20% connectivity) with full (x-axis) or partial E/I overlap (y-axis, colors); different points correspond to different time steps. <b>F.</b> Recall performance as a function of E/I overlap. Asterisks in B and F indicate network configurations that are formally equivalent to the exact dynamics.