Delayed inhibitory feedback sharpens the temporal frequency tuning of relay cells, while delayed excitatory feedback blunts the temporal frequency tuning of relay cells.

<p>Effect of cortical feedback on temporal frequency tuning of relay cells are shown for different values of thalamocortical delay. <i>Panel A</i>: inhibitory feedback only. <i>Panel B</i>: excitatory feedback only. <i>Panel C, left</i>: delayed inhibition, i.e., rapid excitatory feedback combined with long-delay inhibitory feedback ( ms, ms). <i>Panel C, center</i>: synchronized feedback, i.e., excitatory and inhibitory feedback arrive simultaneously ( ms). <i>Panel C, right</i>: delayed excitation, i.e., long-delay excitatory feedback combined with rapid inhibitory feedback ( ms, ms). Full-field grating is used as stimulus (|<b>k</b>_g| ≈ 1<i>deg</i>⁻¹) and default values from <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1006156#pcbi.1006156.t001" target="_blank">Table 1</a> is used for fixed parameters.