Allocentric representations of space in the hippocampus.

The hippocampal-entorhinal system is essential for navigation and memory. The first description of spatially tuned place cell activity in area CA1 of the hippocampus suggested that spatial representations are not centered on self, but are rather allocentric. This idea is supported by extensive neurophysiological data, including temporally coordinated sequential activity during theta phase precession and sharp wave ripples. CA1 pyramidal neurons represent other information as well, such as objects, time, and events. Additionally, our recent research revealed that CA1 place cells jointly represent the spatial location of self and a conspecific, further supporting the idea of allocentric spatial representations by CA1 place cells. The neural mechanisms underlying CA1 spatial representations have long remained a mystery, but recent research examining circuit dynamics and synaptic plasticity suggests that the temporal relationships of inputs from entorhinal cortex layer III and CA3 could be critical for generating spatially tuned CA1 activity. Here, I review studies of the hippocampal representations of space and other features, and discuss the related networks and synaptic mechanisms supporting the representations of these features.