Cosyne 2007 Workshops
February 26-27, 2007
The Canyons, Utah
Adam Johnson
Dynamic representations in the hippocampus: implications for navigation and memory
Neural activity within the hippocampus displays multiple representation modes related to space. During task performance, hippocampal neural activity primarily represents the animal’s current spatial position and has been considered the primary representation mode. Other representation modes occur at short temporal intervals during task performance and sleep. Within these representation modes, hippocampal neural activity remains well-organized and consistent with respect to space, but often reflects positions beyond the animal’s current location. Route replay provides such an example and is prototypical of well-organized spatial representations that are based on previous experience and removed from the animal’s immediate location. We have studied dynamic spatial representations within the hippocampus during solution of T-based decision tasks. Examination of spatial representations at fast time scales revealed transient, but repeatable, phenomena as rats made decisions. These included non-local representations at T-choice points where the location reconstructed from the neural ensemble swept forward, first down one path and then the other. Estimated representations were coherent and preferentially swept ahead of the animal rather than behind the animal — implying they represented future possibilities rather than recently traveled paths. Similar phenomena occurred at other behaviorally salient points (such as in recovery from an error). Forward-shifted spatial representations were influenced by task demands and experience suggesting a mechanism that allows the hippocampus to connect the animal’s current position with future possibilities. These data suggest that the hippocampus does not represent space as a passive computation, but rather that hippocampal spatial processing is an active process likely regulated by cognitive mechanisms.
