Differential effects of ibotenate lesions of the CA1 subfield of the hippocampus on a delayed-nonmatching-to-place task as a function of preoperative training in mice

Abstract

This study examined the effects of ibotenate lesions of the hippocampal CA1 subfield on spatial working memory (delayed-nonmatching-to-place [DNMTP] task) as a function of the existence of preoperative training in mice. The task was varied in its level of difficulty according to either the number of interpolated arm visits (occupied delays) or the length of free time delays imposed between place sample presentation and subsequent recognition. Results indicate that when the tasks were first well learned and the CA1 subfield was subsequently lesioned, only slight impairments were observed during both reacquisition of the DNMTP rule and the problem containing five interpolated visits. When CA1 pyramidal cells were lesioned prior to any training, CA1-lesioned subjects showed general performance deficits regardless of the delay studied (occupied or free). A shift from isolated rule task to the same task tested simultaneously with more difficult variants produced marked performance deficits even for the previously mastered DNMTP rule task. These results suggest that preoperative training reduces subsequent lesion-induced memory deficits and modifies the pattern of postoperative working-memory performance; lesions of the hippocampal CA1 field contribute to the impairments of not only mnemonic capability per se but also reference memory components of the DNMTP task underlying the procedural and cognitive demands required for correct performance of the task. © 1992, Psychonomic Society, Inc.. All rights reserved.