Abstract
Neurons in the dorsolateral geniculate nucleus (dLGN) of the thalamus are contacted by a large number of feedback synapses from cortex, whose role in visual processing is poorly understood. Past studies investigating this role have mostly used simple visual stimuli and anesthetized animals, but corticothalamic (CT) feedback might be particularly relevant during processing of complex visual stimuli, and its effects might depend on behavioral state. Here, we find that CT feedback robustly modulates responses to naturalistic movie clips by increasing response gain and promoting tonic firing mode. Compared to these robust effects for naturalistic movies, CT feedback effects on firing rates were less consistent for simple grating stimuli, likely related to differences in spatial context. Finally, while CT feedback and locomotion affected dLGN responses in similar ways, we found their effects to be largely independent. We propose that CT feedback and behavioral state use separate circuits to modulate visual information on its way to cortex in a context-dependent manner.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
↵1 Senior authors
Significant changes and additions throughout, including: 1. New experiments utilizing direct optogenetic inhibition of L6 CT projecting cells, in addition to global V1 suppression. 2. Separation of analysis of feedback effects by dLGN cell type. 3. Spatial context differentially invoking direct excitatory and indirect inhibitory CT feedback pathways to explain the differential effects of feedback during full-screen naturalistic movie vs. drifting grating stimulation. The main results and conclusions of the manuscript remain unchanged.
