Object-specific activity recorded from C57BL/6J mouse hippocampal CA1 neurons

The rodent hippocampus is an essential neural substrate for spatial memory. This
functional capacity is considered to rely upon a cognitive map that represents the location where
relevant non-spatial items or objects are encountered and where specific events occur within a
contextual or spatial reference frame. Place cell activity recorded from CA1 pyramidal neurons
of the dorsal hippocampus of freely moving rodents is influenced by distal and proximal cues or
items within an environment, and increases when objects are placed into a familiar arena.
Recently, the CA1 region of the rodent dorsal hippocampus was shown to play a vital role in
object-in-context memory, and object memory independent of context; findings consistent with
the cognitive map view. Here, we tested the influence of 3D objects on the spatial firing
properties of CA1 neurons, since object-specific neuronal activity has not yet been fully
established in mouse hippocampus. In vivo extracellular recordings from intermediate dorsal
CA1 yielded simultaneous recordings of place cells and a pyramidal neuron demonstrating
object-specific activity over two consecutive sessions with objects present. Higher frequency
object-specific activity was recorded from the same mouse again 3 weeks later during a
comparable task. Object-specific activity was observed only when the mouse explored objects in
the arena, and was independent of spatial location or object identity. Recordings from more distal
region of dorsal CA1, which receives input from proximal CA3, yielded two additional neurons
that demonstrated comparable object-related activity. These results further support the
involvement of the rodent hippocampus in non-spatial object memory.