Abstract
The largest targets of retinal input in mammals are the dorsal lateral geniculate nucleus (dLGN), a relay to the primary visual cortex (V1), and the superior colliculus. V1 innervates and influences the superior colliculus. Here, we find that, in turn, superior colliculus modulates responses in mouse V1. Optogenetically inhibiting the superior colliculus reduces responses in V1 to optimally sized stimuli. Superior colliculus could influence V1 via its strong projection to the lateral posterior nucleus (LP/Pulvinar) or its weaker projection to the dLGN. Inhibiting superior colliculus strongly reduces activity in LP. Pharmacologically silencing LP itself, however, does not remove collicular modulation of V1. The modulation is instead due to a collicular gain modulation of the dLGN. Surround suppression operating in V1 explains the different effects for differently sized stimuli. Computations of visual saliency in the superior colliculus can thus influence tuning in the visual cortex via a tectogeniculate pathway.
Highlights
The largest targets of retinal input in mammals are the dorsal lateral geniculate nucleus, a relay to the primary visual cortex (V1), and the superior colliculus
Visual information flows from the retina to the dorsal lateral geniculate nucleus where it is relayed to the primary visual cortex (V1)
We investigated the influence of superior colliculus on the visual responses in the mouse primary visual cortex
Summary
The largest targets of retinal input in mammals are the dorsal lateral geniculate nucleus (dLGN), a relay to the primary visual cortex (V1), and the superior colliculus. The superior colliculus could potentially influence the input to the primary visual cortex through its projection to the shell of the dLGN12 This tectogeniculate projection is anatomically present in all studied mammals[13], but there has been no evidence that it has a functional effect on thalamocortical visual processing. We wanted to investigate if the computation of such a saliency map in the superior colliculus could influence neural responses in the primary visual cortex, even in a situation where visual attention does not play any role. We found that optogenetically silencing superior colliculus reduced response in V1 to optimally sized stimuli This effect is not via the strong SC to LP pathway, but via the anatomically smaller tectogeniculate pathway. A size-independent gain modulation of the dLGN by the superior colliculus is transformed into a size-dependent gain modulation in V1
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