Cell-type specific binocular interactions in mouse visual thalamus

Projections from each eye are segregated in separate domains within the dorsal lateral geniculate nucleus (dLGN). Yet, in vivo studies indicate that the activity of single dLGN neurons can be influenced by visual stimuli presented to either eye. In this study we explored whether intrinsic circuits mediate binocular interactions in the mouse dLGN. We employed dual color optogenetics in vitro to selectively activate input from each eye and recorded synaptic responses in thalamocortical (relay) cells as well as inhibitory interneurons, which have extensive dendritic arbors that are not confined to eye specific domains. While most relay cells received monocular retinal input, most interneurons received binocular retinal input; consequently, the majority of dLGN relay cells received binocular retinogeniculate-evoked inhibition. Moreover, in recordings from adjacent pairs of relay cells and interneurons, the most common relationship observed was binocular excitation of interneurons paired with binocular inhibition of adjacent relay cells. Finally, we found that dLGN interneurons are interconnected, displaying both monocular and binocular inhibition in response to retinal activation. In sum, our results indicate that geniculate interneurons provide one of the first locations where signals from the two eyes can be compared, integrated, and adjusted before being transmitted to cortex, shedding new light on the role of the thalamus in binocular vision. Highlights In vitro dual color optogenetics examined convergence of eye-specific retinal inputs to thalamocortical (relay) cells and interneurons in the dLGN The majority of relay cells receive monocular excitatory retinogeniculate input while the majority of interneurons receive binocular input Binocular relay cells are located in and around the ipsilateral patch whereas binocular interneurons are distributed throughout the dLGN The majority of relay cells receive binocular retinogeniculate-evoked inhibition dLGN interneurons are interconnected, receiving both monocular and binocular retinogeniculate-evoked inhibition