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

<p><i>Upper left</i>: the two dimensional spatial structure of the impulse-response function. <i>Bottom left</i>: one-dimensional plot of the impulse-response function. Center excitation and surround inhibition correspond to the maximum and minimum value of (<b>r</b>), respectively, while where the zero-crossing occurs is used as an indication for the receptive field size. <i>Right</i>: spatial impulse-response function for different circuit configurations. In each case all other contributions are removed, except feedforward excitation. Default parameters from <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1006156#pcbi.1006156.t001" target="_blank">Table 1</a> have been used.