Thalamic stimulation evokes feedforward inhibition in layer V pyramidal cells (A and B) but not in layer II-IV pyramidal cells (C and D) or in interneurons (E and F). Cells were hyper- and depolarized about ERest with 250-ms current steps, and thalamic afferents stimulated at constant intensity (A, C, and E, top). Responses were then normalized and aligned (A, C, and E, bottom) and the time integral of the response computed (J PSP; B, D, and F, large symbols). This analysis was repeated for all cells in which ≥3 membrane potentials were tested (B, D, and F, small symbols). For pyramidal cells in layer V, inhibition was apparent in the responses and JPSP(Vm) had significant negative slope (B). For pyramidal cells in layers II-IV (D) and interneurons (F), no inhibition was apparent and JPSP(Vm) did not have significant negative slope. Resting potentials were -78.2 mV (A), -75.1 (C), -67.9 mV (E). Scale bars: 100 ms, 10 mV (A and C, top); 100 ms, 6 mV (E, top); 10 ms (A, C, and E, bottom).