The hippocampus as a spatial map. Preliminary evidence from unit activity in the freely-moving rat

Early work on place cells in the hippocampus of rats revealed that specific neurons encode an animal's position in a two-dimensional space.

“Early work on place cells in the hippocampus of rats revealed that specific neurons encode an animal's position in a two-dimensional space [44,45].”

Place cells encode the animal's position in an environment and, more generally, events of episodic experience, and have been causally linked to memory functions.

“These neurons encode the animal’s position in an environment1 and, more generally, events of episodic experience2–4 and have been causally linked to memory functions5–7.”

PCs have been comprehensively identified only in the hippocampus of birds and mammals.

“Notably, PCs have been comprehensively identified only in the hippocampus of birds16 and mammals5,17.”

The previous lack of evidence for PCs outside mammalian and avian species suggests either that the neural architecture needed to generate PCs evolved following the emergence of land vertebrates or that PCs in species such as teleost fish have not yet been discovered due to methodological limitations.

“The previous lack of evidence for PCs outside of mammalian and avian species suggests either that the neural architecture needed to generate PCs evolved following the emergence of land vertebrates5,16 or that PCs in species such as teleost fish have not yet been discovered, potentially due to methodological limitations (for example, sparse recordings or tethered preparations).”

Place cells, hippocampal neurons that fire when the animal occupies a particular location, are proposed as the higher instance of a brain system that builds map-like spatial memory representations anchored in the external world, contributing to allocentric navigation.

“The “place cells”, i.e., hippocampal neurons that fire when the animal occupies a particular location of the space, have been proposed to be the higher instance of a brain system that builds up map-like spatial memory representations anchored in the external world, contributing to the neural computations required for allocentric navigation [39,72,74,197,198].”

Place cells in the mammalian hippocampus preferentially fire when an animal is in a particular spatial location.

“Furthermore, specific cells within the mammalian hippocampus, known as ‘place cells’ [115], preferentially fire when an animal is in a particular spatial location”

The receptive fields of place cells in the rodent HPC are sensitive to specific locations in space.

“Analogous to the selectivity of concept cells, the receptive fields of place cells in the rodent HPC are sensitive to specific locations in space 60,61 .”

In rodents, location information is encoded by place and grid cells in the hippocampal formation, and directional information is coded by head direction cells in Papez circuit structures.

“In rodents, location information is encoded by place and grid cells in the hippocampal formation,1, 2 and directional information is coded by head direction (HD) cells in Papez circuit structures3”