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Abstract
The entorhinal cortex provides the primary cortical projections to the hippocampus, a brain structure critical for memory. However, it remains unclear how the precise firing patterns of medial entorhinal cortex (MEC) cells influence hippocampal physiology and hippocampus-dependent behavior. We found that complete bilateral lesions of the MEC resulted in a lower proportion of active hippocampal cells. The remaining active cells had place fields, but with decreased spatial precision and decreased long-term spatial stability. In addition, MEC rats were as impaired in the water maze as hippocampus rats, while rats with combined MEC and hippocampal lesions had an even greater deficit. However, MEC rats were not impaired on other hippocampus-dependent tasks, including those in which an object location or context was remembered. Thus, the MEC is not necessary for all types of spatial coding or for all types of hippocampus-dependent memory, but it is necessary for the normal acquisition of place memory.
Highlights
Long-term memory for facts and events is thought to depend on the interaction of the hippocampus with widespread neocortical sites (McClelland et al, 1995; Squire and Alvarez, 1995)
The medial entorhinal cortex (MEC) is densely connected with the postrhinal cortex and is hypothesized to be specialized for representing spatial information, while the lateral entorhinal cortex (LEC) is densely connected with the perirhinal cortex and is thought to be specialized for representing object information (Witter et al, 2000; Knierim et al, 2006; Eichenbaum et al, 2012)
To determine whether spatial computations in MEC support spatial memory, we developed a precise set of surgical coordinates for removing the entire MEC, including the most extreme portion of the dorsocaudal MEC
Summary
Long-term memory for facts and events is thought to depend on the interaction of the hippocampus with widespread neocortical sites (McClelland et al, 1995; Squire and Alvarez, 1995). Within the MEC, grid cells are intermingled with other spatially and directionally modulated cell types such as head direction cells, conjunctive head direction-grid cells, border cells, and spatially periodic non-grid cells (Hafting et al, 2005; Sargolini et al, 2006; Solstad et al, 2008; Krupic et al, 2012) All of these cell types have been identified as projecting directly from the MEC to the dorsal hippocampus (Zhang et al, 2013) and are thought to be the primary source of spatial information for hippocampal place cells
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