The effects of lesions to the rat hippocampus or rhinal cortex on olfactory and spatial memory: retrograde and anterograde findings |
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Authors: | Kaut K P Bunsey M D |
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Institution: | Department of Psychology, University of Akron, 318F Polsky Building, 225 S. Main Street, Akron, OH 44325-4301, USA. kpk@uakron.edu |
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Abstract: | The role of the hippocampal system in retrograde and anterograde amnesia was investigated by using a novel olfactory-guided
paradigm and a traditional test of spatial learning. In the retrograde study, rats were trained on a sequence of two-choice
olfactory discriminations in the weeks prior to receiving neurotoxic lesions of the hippocampus or aspiration lesions of the
perirhinal-entorhinal cortex. Memory tests for preoperatively learned discriminations revealed no statistical impairment for
subjects with damage to the hippocampus on a problem learned remote in time from surgery (i.e., 4 weeks +) or on the two recently
learned discriminations (i.e., 1–3 weeks prior to surgery). The performance of subjects with perirhinal-entorhinal damage
provided an important comparison for subjects with specific hippocampal lesions. Despite showing intact memory for the remotely
learned problem, perirhinalentorhinal damage resulted in numerically (although not significantly) weaker performance on postoperative
tests of retention for the discriminations learned in the 3 weeks prior to surgery. In the anterograde portion of the study,
long-term memory for newly acquired discriminations was spared in subjects with damage to the hippocampus, whereas subjects
in the perirhinal-entorhinal lesion group again showed the weakest memory performance on these tests of 5-day retention. Postoperative
water maze learning was uniformly impaired in subjects with damage to the hippocampus and perirhinalentorhinal cortex, thus
confirming the effect of these lesions and supporting the involvement of these brain areas in spatial processes. These findings
further dissociate the specific involvement of the hippocampus in tasks of a spatial-relational nature versus nonrelational
tasks, such as discrimination learning and recognition memory (e.g., Duva et al., 1997; Eichenbaum, 1997; Eichenbaum, Schoenbaum,
Young, & Bunsey, 1996). Moreover, the results suggest that damage to the hippocampus itself does not contribute to retrograde
or anterograde memory impairments for all types of information, whereas the data suggest a more important role for the perirhinal-entorhinal cortex in recognition
memory, irrespective of modality. |
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