Figure 2.

RF properties of SOM and PV inhibitory neurons in layer 4. A, An example SOM neuron. A₁, Spatial RF. Left, Average spike shape. Middle, Array of poststimulus spike time histograms (PSTHs, bin size = 50 ms) for responses to individual On or Off stimuli. Each pixel represents 5° in visual space. Calibration: 17.5 Hz, 200 ms. Right, Color map represents the superimposed spiking On (red) and Off (green) subfields. The brightness of the color represents the firing rate. The maps were smoothed by bilinear interpolation. The one-dimensional map below displays responses to flashing bars of optimal orientation (indicated by the white bar in the square map) at various locations. A₂, Cycle average of spike responses evoked by drifting sinusoidal grating at optimal spatial frequency. The modulation ratio F1/F0 is indicated. A₃, Polar plot of responses to moving gratings at 12 directions. The moving direction is orthogonal to the orientation of the grating. Numbers in parentheses represent the axial scale: the average number of evoked spikes with baseline subtracted. The global orientation selectivity index (OSI) is indicated. B, An example PV neuron. Data are presented in the same way as in A. Calibration: 70 Hz, 200 ms in B₁. C, Distribution of overlap indices (OI) for different groups of neurons. N = 12, 10 and 14, respectively. Solid symbol represents the mean value. Error bar, SD. **p < 0.01. D, Distribution of modulation ratios for SOM, PV and excitatory neurons. N = 30, 8 and 22. *p < 0.05, **p < 0.01, t test. E, Distribution of subfield sizes. The subfield size is the average of that of On and Off subfields if both were detected. N = 20, 12, and 14. **p < 0.01. F, Distribution of OSI. N = 37, 10 and 34. **p < 0.01. G, Distribution of direction selectivity indices (DSI). N = 37, 10 and 34. **p < 0.01.