Neural circuits underlying visual representation in the medial entorhonal cortex

SUMMARY The ability of an animal to successfully navigate the world and carry out goal-directed behavior is dependent on the hippocampus and entorhinal cortex but is also strongly shaped by visual information derived from external cues. Indeed, manipulation or elimination of visual input can significantly disrupt ongoing activity in these regions and impair tasks that require accurate internal representations of the local environment. Considerable anatomical data indicate that the occipital cortex, including primary and higher-order visual areas, sends projections to the medial entorhinal cortex (MEC). However, the ability of MEC neurons to encode visual cues and the specific circuits mediating this function are largely unknown. Whether the MEC can respond to low-level visual features or primarily represents complex, behaviorally salient relationships between stimuli has not been examined. Furthermore, how visual inputs interact with ongoing network activity within the MEC is unclear. In the present study, we propose a combination of electrophysiology, anatomical tracing, optogenetic manipulation, and ex vivo synaptic physiology to (1) determine the capacity for visual stimulus representation by MEC neurons, (2) identify the afferent pathways and specific subpopulations of MEC neurons that encode visual input, (3) determine the microcircuit organization of connections within the MEC that shape visual responses, and (4) link visually-evoked MEC activity to virtual navigation for reward. Our overall goal is to understand the pathways by which visual information guides complex behaviors such as navigation through the environment. We expect that our results will generate new avenues for exploring both the cellular and circuit foundations of visual behavior and the mechanisms underlying coordination of activity between different brain regions.