Synaptic mechanisms of context-dependent sensory responses in the hippocampus

As animals navigate, they must identify features in context. The hippocampus-a structure critical for navigation-exhibits a different code for each environment, uniquely representing locations and objects within each environment in the firing rates of its neurons. It is unknown how or where these context-specific codes emerge. For example, it is unknown whether pyramidal neurons in the CA1 subregion produce these codes (by combining separate inputs from local sensory cues and the environmental context) or inherit conjunctive codes from upstream brain areas. We performed electrical recordings in the hippocampus as mice navigated in two distinct virtual environments. In CA1, subthreshold synaptic responses to a visual cue in one environment were absent when the same cue occurred in the second environment. In CA3, cue-driven spiking also strongly depended on environmental context. These results indicate that context-dependent sensory coding in CA1 is inherited from its CA3 input.