Figure 3. Excitatory, inhibitory, and membrane potential orientation selectivity. A, An example neuron for which conductances were estimated using voltage clamp. The top row indicates the membrane potential orientation selectivity recorded in current clamp (black traces, calibration: 2 mV). Predictions of membrane potential responses based on estimated conductances are also shown (cyan traces). The second row shows the currents measured when the neuron was voltage clamped at −16 mV (light blue) and −81 mV (light red, calibration: 20 pA). Excitatory and inhibitory conductances (blue and red traces, respectively, calibration: 0.4 nS) are shown for each orientation. B, Orientation selectivity for membrane potential (top, peak = 1.3 mV), excitatory conductance (middle, peak = 0.18 nS), and inhibitory conductance (bottom, peak = 0.32 nS). Error bars indicate the SEM. C, An example cell for which conductances were estimated using current clamp. The top panels show the membrane potential responses as the neuron was injected with 210, −30, or −173 pA (from black traces to gray traces). Excitatory and inhibitory conductances derived from those measurements are shown in the bottom traces (Ge, blue traces; Gi, red traces; calibration: 5 nS). Shaded regions indicate the 95% confidence intervals derived from bootstrap analysis. D, Orientation selectivity for membrane potential (extracted from the data taken when the neuron was hyperpolarized, peak = 12 mV), excitatory conductances (middle, peak = 3 nS), and inhibitory conductances as in B (peak = 2.2 nS). The inset values in these panels indicate the OSI for each tuning curve. The relationship between injected current and observed membrane potential is plotted for the three epochs indicated by arrows in C.