Cell type specific binocular interactions

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 and most relay cells received binocular retinogeniculate-evoked inhibition. In recordings from closely-spaced pairs of relay cells and interneurons, the most common relationship observed was retinogeniculate excitation of interneurons paired with inhibition of relay cells via activation of inputs from the same eye(s). Moreover, relay cells that received binocular inhibition were located in and around the ipsilateral patch of retinogeniculate terminals, suggesting that interneuron output is spatially related to retinal input. 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.