Cellular and circuit mechanisms underlying binocular vision

How binocular visual information is combined at the level of single neurons in the brain is not fully understood. Here, we show in mice that callosal input from the opposite visual cortex (V1) plays a critical role in this process. In vivo we find this callosal projection carries ipsilateral eye information and synapses exclusively onto binocular neurons. Using the presence of callosal input to identify binocular neurons in vitro, at the cellular level we show that binocular neurons are less excitable than monocular neurons due to high expression of Kv1 potassium channels. At the circuit level we find that only monocular neurons send callosal projections to the opposite V1, whereas binocular neurons do not. Finally, using dual-colour optogenetics we show that most binocular and monocular neurons receive direct input from the thalamus. In summary, we describe distinct cellular and circuit mechanisms underlying processing of binocular visual information in mouse V1.