Optogenetic activation of visual thalamus generates artificial visual percepts

The lateral geniculate nucleus (LGN), a retinotopic relay center where visual inputs from the retina are processed and relayed to the visual cortex, has been proposed as a potential target for artificial vision. At present, it is unknown whether optogenetic LGN stimulation is sufficient to elicit behaviorally relevant percepts and the properties of LGN neural responses relevant for artificial vision have not been thoroughly characterized. Here, we demonstrate that tree shrews pretrained on a visual detection task can detect optogenetic LGN activation using an AAV2-CamKIIα-ChR2 construct and readily generalize from visual to optogenetic detection. We also characterize how amplitude and frequency of optogenetic stimulation affect behavioral performance. Given the importance of temporal stimulation parameters, we also study tree shrew behavioral ability to discriminate among pairs of visual flicker frequencies and demonstrate performance transfer among related discrimination problems as well as limitations. Neural recordings in LGN and primary visual cortex (V1) examining two flicker discriminations reveal that while LGN neurons multiplex information about temporal stimulation discriminations, V1 neurons explicitly encode information about one or the other discriminations but not both. Our findings confirm the LGN as a potential target for visual prosthetics and introduce a distinction in stimulus encoding between thalamic and cortical representations that could be of fundamental importance in artificial vision.