Hippocampal contribution to maintenance of entorhinal grid fields
Saturday, Nov 13, 2010, 4:00 PM - 5:00 PM
, M. FYHN, T. HAFTING, D. DERDIKMAN, E. I. MOSER, M.-B. MOSER;
Ctr. for the Biol. of Memory, NTNU, Trondheim, Norway
The presence of a network of grid cells and head-direction cells in the medial entorhinal cortex (MEC) points to MEC as a key structure for dynamic representation of location. While it is hypothesized that these cells depend strongly on self-motion information, the fields are remarkably stable between tests in the same environment, suggesting that the entorhinal map is anchored by association to external landmarks. To determine if these associations are stored in the hippocampus, we temporally inactivated the hippocampus by local infusion of the GABA-A agonist muscimol while recording place cells in CA1 and grid cells and head-direction cells in superficial layers of the MEC in freely moving rats.
The hippocampal firing rate dropped to zero about 20 minutes after infusion. Within 40 minutes after hippocampal inactivation the grid cell firing rate in the MEC dropped to approximately 50%. At this point, the grid pattern disappeared from the time-averaged rate maps. At the same time, a substantial number of the grid cells in layers II and III developed strong head-direction preferences, even if no directional firing was present in the undrugged condition. During the inactivation, population rate maps for successive time epochs were better correlated with preceding or succeeding epochs than with the initial baseline map. Temporal correlations between grid cell pairs, examined for individual running directions, were maintained after disappearance of the grid in the rate map, suggesting that the correlation structure of the network persists in the absence of clear grid fields. Six hours after infusion all measures of grid structure were restored. Taken together, these results suggest that the general activity level of entorhinal grid cells depends on input from the hippocampus. Left without this input, grid cells may be influenced to a larger extent by the head-direction system. The gradual deformation of grid fields in the absence of hippocampal output suggests that the entorhinal-hippocampal network operates as a functional unit where the hippocampus provides the entorhinal network with stored associations that anchor the grid to external landmarks.
Norw Res Council Ctr of Excellence grant
[Authors]. [Abstract Title]. Program No. XXX.XX. 2010 Neuroscience Meeting Planner. San Diego, CA: Society for Neuroscience, 2010. Online.
2010 Copyright by the Society for Neuroscience all rights reserved. Permission to republish any abstract or part of any abstract in any form must be obtained in writing by SfN office prior to publication.
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