Neural encoding of the concept of nest in the mouse brain.

As important as memory is to our daily functions, the ability to extract fundamental features and commonalities from various episodic experiences and to then generalize them into abstract concepts is even more crucial for both humans and animals to adapt to novel and complex situations. Here, we report the neural correlates of the abstract concept of nests or beds in mice. Specifically, we find hippocampal neurons that selectively fire or cease to fire when the mouse perceives nests or beds, regardless of their locations and environments. Parametric analyses show that responses of nest cells remain invariant over changes in the nests' physical shape, style, color, odor, or construction materials; rather, their responses are driven by conscious awareness and physical determination of the categorical features that would functionally define nests. Such functionality-based abstraction and generalization of conceptual knowledge, emerging from episodic experiences, suggests that the hippocampus is an intrinsic part of the hierarchical structure for generating concepts and knowledge in the brain.