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Excitotoxic lesions of the pre‐ and parasubiculum disrupt the place fields of hippocampal pyramidal cells

To determine what influence the pre‐ and parasubiculum regions of the hippocampal formation have on neural representations within the dorsal hippocampus, single‐unit recordings were made as rats with bilateral ibotenic acid lesions centered on the former regions (n = 4) or control surgeries (n = 3) foraged freely. Spatial firing specificity was measured using an information content procedure. Cells from lesioned animals (n = 57) provided significantly less spatial information than cells from control animals (n = 44). Whereas some degree of location‐related activity (place fields) was observed in 98% of neurons recorded from control animals, it was observed in only 65% of the neurons from lesioned animals. The spatial resolution of the intact place fields appeared to be compromised in lesioned animals as a result of their having a higher firing rate outside the place field. These findings indicate that the pre‐ and parasubiculum regions have a major role in maintaining the specificity of the place field firing of hippocampal pyramidal cells. Since previous data indicate that these lesioned animals displayed delay‐dependent deficits in spatial tasks, these findings also suggest that a disruption in place field activity may be a causal factor in this spatial memory deficit. © 2003 Wiley‐Liss, Inc.