Abstract
Environmental cues affect place cells responses, but whether this information is integrated versus segregated in distinct hippocampal cell populations is unclear. Here, we show that, in mice running on a treadmill enriched with visual-tactile landmarks, place cells are more strongly controlled by landmark-associated sensory inputs in deeper regions of CA1 pyramidal layer (CA1d). Many cells in CA1d display several firing fields correlated with landmarks, mapping positions slightly before or within the landmarks. Supporting direct involvement of sensory inputs, their firing fields show instantaneous responses to landmark manipulations, persist through change of context, and encode landmark identity and saliency. In contrast, cells located superficially in the pyramidal layer have single firing fields, are context specific and respond with slow dynamics to landmark manipulations. These findings suggest parallel and anatomically segregated circuits within CA1 pyramidal layer, with variable ties to landmarks, allowing flexible representation of spatial and non-spatial information.
Highlights
Environmental cues affect place cells responses, but whether this information is integrated versus segregated in distinct hippocampal cell populations is unclear
Non-spatial information from the lateral entorhinal cortex (LEC)[11,12,13,14,15,16] and spatial information from the medial entorhinal cortex (MEC)[17,18] target the proximal and distal regions of CA1, respectively[19,20], underlying differences in place field tuning along the proximodistal axis[11,21]
Place cells are typically studied in open arena and maze environments rich with visual cues, which can pose a problem for discerning place field mechanisms
Summary
Environmental cues affect place cells responses, but whether this information is integrated versus segregated in distinct hippocampal cell populations is unclear. Cells located superficially in the pyramidal layer have single firing fields, are context specific and respond with slow dynamics to landmark manipulations. These findings suggest parallel and anatomically segregated circuits within CA1 pyramidal layer, with variable ties to landmarks, allowing flexible representation of spatial and non-spatial information. We used a treadmill apparatus, in which the only useful landmarks were small objects fixed on the belt, and in which mice ran with their head restrained[30] We recorded in both hippocampal CA1 and CA3 regions using multi-site silicon probes, and we examined the impact of landmarks and landmark manipulations on the firing fields of pyramidal cells. These findings demonstrate a functional organization of place field mechanisms, and bring new insights to the underlying mechanisms of landmark-vector representation
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