Fig 4. Cortical feedback modulates the center-surround receptive fields of relay cells.

Upper left: the two dimensional spatial structure of the impulse-response function. Bottom left: one-dimensional plot of the impulse-response function. Center excitation and surround inhibition correspond to the maximum and minimum value of ${\mathcal{F}}_{\text{spatial}}^{-1}\left\{{\tilde{W}}_{\mathrm{R}}^{\text{spatial}}\left(\mathbf{k}\right)\right\}$(r), respectively, while where the zero-crossing occurs is used as an indication for the receptive field size. Right: spatial impulse-response function for different circuit configurations. In each case all other contributions are removed, except feedforward excitation. Default parameters from Table 1 have been used.