Figure 2. Effect of behavioral state on the tuning of V1 neurons in the orientation and spatial-frequency (Fourier) plane. A, Tuning of four sample cells in the Fourier domain (origin is at the center) and their corresponding temporal kernels (bottom). These estimates were obtained by fitting a linear model to the data (Materials and Methods, Eq. 2). All temporal kernels are shown starting at t = 0. Spatial frequency along the horizontal meridian is represented by ωx and the spatial frequency along the vertical meridian by ωy. All Fourier kernels share the same pseudocolor scale. Positive values (red hues) represent stimuli with orientation and spatial frequency that led to increases in the response of the cell; negative values (blue hues) represent stimuli that suppressed the response of the cell; neutral stimuli are represented by a green hue. B, Distribution of peak kernel positions in the Fourier domain across the population. The distribution is symmetric because the Fourier kernel is symmetric. C, Top, Distribution of preferred orientations, θ. Bottom, Distribution of preferred spatial frequencies, ω = . The symmetry of preferred orientations is a consequence of the symmetry of the Fourier kernels as well. Only well fit neurons (cross-validated r > 0.15, n = 3476; see Materials and Methods for details) are considered in this analysis. D, Tuning of four sample cells in the Fourier domain during rest (top) and locomotion (bottom). Temporal responses are shown in the middle (blue: rest, red: locomotion). This was obtained by fitting a model that allowed changes in gain between locomotion and rest (Materials and Methods, Eq. 6). E, Preferred spatial frequency and orientation are largely preserved across states. F, Response gain increases substantially during locomotion. G, There is a small but significant increase in baseline firing rate of 0.12 ± 0.01 SDs of the response during locomotion (p < 0.001, bootstrap test).