(A) Schematic of a local conductance-based E-I network with mutually coupled excitatory (E) and inhibitory (I) units. A fraction (50%) of the E units are sensitive to 'optical' stimulation. , self-excitation among E units;, self-inhibition among I units;, excitation provided by E to I; , inhibition provided by I to E. (B) Simulation of a network of 800 E and 200 I units (). The raster plot shows the activity of all units in the model (blue, I; green, E without opsin; magenta, E with opsin) to a step input () and 4Hz sinusoidal optical stimulation (). (C) Population spiking rate averaged across 1000 simulations of the scenario in (B) with and without optical stimulation. (blue, I; orange, all E; green, E without opsin; magenta, E with opsin. solid lines, with optical stimulation; dashed lines, without optical stimulation) (D) Spike- spike coherence (SSC) among E units was calculated for the two conditions with and without optical stimulation and the change in SSC across the two conditions was calculated as a modulation index (SSC MI). SSC MI exhibits a peak at 4Hz due to optical stimulation.