Effects of corticothalamic feedback depend on visual responsiveness and stimulus type

In the dorsolateral geniculate nucleus (dLGN) of the thalamus, stimulus-driven signals combine with modulatory inputs such as corticothalamic (CT) feedback and behavioral state, but their impact in shaping dLGN activity is debated. We recorded extracellular responses in the dLGN of mice viewing a movie stimulus, while photosuppressing CT feedback and tracking locomotion and pupil size. Using generalized linear models fit to single neuron responses, we found that including CT feedback and behavioral state improved model predictions, especially for a subpopulation of neurons poorly responsive to the movie. Intriguingly, the impact of CT feedback was stronger without a patterned visual stimulus. Finally, for neurons sensitive to CT feedback, visual stimuli could be more easily discriminated when CT feedback was suppressed. Together, these results show that the effects of modulatory inputs in dLGN depend on visual responsiveness and stimulus type, with CT feedback affecting sensitivity and reliability, potentially to tune the thalamic relay.