The neural basis of spatial memory

I present single unit recording data on the neural basis of sense-of-location in the Hippocampus and Entorhinal cortex. I argue that this involves a compromise between the hippocampally mediated environmental information and entorhinally mediated short-term path integration, in which the relevant environmental information is the set of distances to extended geometrical features (boundaries) ordered by their allocentric direction.

I present behavioural evidence that human memory for the locations of objects is consistent with the presence of these allocentric hippocampal representations in combination with egocentric sensory representations.

Neuropsychological and functional neuroimaging experiments using virtual reality indicate that the human Hippocampus supports an allocentric representation of environmental geometry useful for remembering locations. By contrast, the dorsal striatum support representations of locations or turns relative to individual landmarks. I show that both types of representation are available over both short and long durations, undermining the classical dissociation between long-term and short-term memory.

Nonetheless, I argue that hippocampal representations of spatial (and possibly temporal) context may be specifically useful for long-term memory, while short-term egocentric medial parietal representations must be generated for visuo-spatial imagery of the products of retrieval. In addition I show that, while striatally mediated learning of locations relative to landmarks obeys associative learning theory, hippocampally mediated learning about locations relative to environmental boundaries does not.