Effects of non-retinal inputs in visual thalamus depend on visual responsiveness and stimulus context

In the dorsolateral geniculate nucleus (dLGN) of the thalamus, stimulus-driven signals are combined with modulatory inputs such as corticothalamic (CT) feedback and behavioural state. How these shape dLGN activity remains an open question. We recorded extracellular responses in dLGN of awake mice to a movie stimulus, while photosuppressing CT feedback, and tracking locomotion and pupil size. To assess the relative impact of stimulus and modulatory inputs, we fit single neuron responses with generalized linear models. While including CT feedback and behavioural state as predictors significantly improved the models overall performance, the improvement was especially pronounced for a subpopulation of neurons poorly responsive to the movie stimulus. In addition, the observed impact of CT feedback was faster and more prevalent in the absence of a patterned visual stimulus. Finally, for neurons that were sensitive to CT feedback, visual stimuli could be more easily discriminated based on spiking activity when CT feedback was suppressed. Together, these results show that effects of modulatory inputs in dLGN depend on visual responsiveness and stimulus type.