Modality-specific Subpopulations of Place Fields Coexist in the Hippocampus.

Hippocampal place cells integrate signals from multiple sensory modalities. However, it is unclear how these different inputs are combined to generate place fields. We investigated how visual spatial cues and an animal's locomotion are integrated by CA3 place cells of Mongolian gerbils. While the animals moved on a virtual linear track, we adapted the gain between the visually projected environment and the treadmill movement. Place cells responded differently to this manipulation. In a subset, place fields were kept in accord with salient visual cues in the virtual environment or reward location, whereas in another subset, place fields were strongly influenced by locomotion. Theta phase precession was present and indistinguishable between the place field types. Theta compression remained intact under gain changes and extended over both types of place field. Hippocampal place cells thus retain strong influence from distinct input streams suggesting a role of the hippocampus CA3 as a multimodal associator on the theta time scale.