Response of model neurons to flashed square stimuli under different current injection levels. The four columns of the figure show data from four representative excitatory cortical model neurons. A, C, Receptive field maps (light for ON subfield, dark for OFF subfield) with the position of the contrast-matched square stimulus (A) and contrast-mismatched square (C) stimulus overlaid on the stimulation grid. Grid spacing was 0.3°. B, D, Top, Traces indicate conductance changes (gE, red; gI, blue). Bottom, Traces indicate membrane potential (black line). B, response to contrast-matched stimulus. D, response to contrast-mismatched stimulus. E–G, Voltage response to contrast-mismatched stimulus during + 0.1 nA (E), −0.1 nA (F), and −0.2 nA (G) current injection. H, Total synaptic conductance change from baseline calculated following the same procedure as in Hirsch et al. (1998). Stimulus presentation is indicated by black bar under each voltage trace.