Since the proposal of O'Keefe and Nadel (1978), decades of work have supported a specialized role for the hippocampus in coding allocentric spatial memories, or spatial memories referenced to external landmarks. Foremost among the evidence for this theoretical view are 1) the presence of place cells in both the rodent and primate hippocampus and 2) the fact that hippocampal lesions impair performance on allocentric spatial tasks. Recent findings from rodents and humans, however, challenge the idea that the hippocampus is necessary or even involved in all forms of allocentric spatial coding. Grid cells, located outside of the hippocampus in entorhinal cortex, would appear sufficient to drive many allocentric computations. Furthermore, several human studies suggest the importance of retrosplenial and parahippocampal cortex, rather than the hippocampus, in allocentric spatial coding. The consensus from these studies seems to be that multiple brain regions outside of the hippocampus possess the neural architecture necessary for allocentric spatial coding. This leaves open the possibility that the hippocampus is: 1) still an integral part of this network or 2) minimally or not involved in allocentric coding. Several possible considerations thus emerge from these two perspectives, including: 1) could the hippocampus be involved more generally in relational memory or spatiotemporal contextual coding? 2) what are the appropriate ways of assessing allocentric and egocentric spatial coding? 3) what behavioral paradigms are appropriate for testing spatial memory? 4) are there reasons that fMRI may occasionally "miss" hippocampal involvement? 5) what are the precise roles of other brain regions, such as parahippocampal and retrosplenial cortex, play in spatial coding? 6) do place cells and grid cells represent independent spatial codes capable of operation in isolation? 7) are there possible interspecies differences (i.e., between rats and humans) in spatial coding? We encourage submissions from all members of the neuroscience and behavioral psychology community who wish to contribute to this import debate on spatial cognition.
Since the proposal of O'Keefe and Nadel (1978), decades of work have supported a specialized role for the hippocampus in coding allocentric spatial memories, or spatial memories referenced to external landmarks. Foremost among the evidence for this theoretical view are 1) the presence of place cells in both the rodent and primate hippocampus and 2) the fact that hippocampal lesions impair performance on allocentric spatial tasks. Recent findings from rodents and humans, however, challenge the idea that the hippocampus is necessary or even involved in all forms of allocentric spatial coding. Grid cells, located outside of the hippocampus in entorhinal cortex, would appear sufficient to drive many allocentric computations. Furthermore, several human studies suggest the importance of retrosplenial and parahippocampal cortex, rather than the hippocampus, in allocentric spatial coding. The consensus from these studies seems to be that multiple brain regions outside of the hippocampus possess the neural architecture necessary for allocentric spatial coding. This leaves open the possibility that the hippocampus is: 1) still an integral part of this network or 2) minimally or not involved in allocentric coding. Several possible considerations thus emerge from these two perspectives, including: 1) could the hippocampus be involved more generally in relational memory or spatiotemporal contextual coding? 2) what are the appropriate ways of assessing allocentric and egocentric spatial coding? 3) what behavioral paradigms are appropriate for testing spatial memory? 4) are there reasons that fMRI may occasionally "miss" hippocampal involvement? 5) what are the precise roles of other brain regions, such as parahippocampal and retrosplenial cortex, play in spatial coding? 6) do place cells and grid cells represent independent spatial codes capable of operation in isolation? 7) are there possible interspecies differences (i.e., between rats and humans) in spatial coding? We encourage submissions from all members of the neuroscience and behavioral psychology community who wish to contribute to this import debate on spatial cognition.
