Effects of Neonatal Hippocampal Lesions on Contextual Learning and Memory in Monkeys Open Access

Glavis-Bloom, Courtney (2010)

Permanent URL: https://etd.library.emory.edu/concern/etds/7s75dc75n?locale=en
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Abstract

A large body of evidence stemming from electrophysiological recordings, neuroimaging, lesion, and developmental studies has provided strong support to the assertion that the hippocampus is critical for accurate contextual learning and memory. Developmental lesion studies in primates are inconclusive as regards to the role of the hippocampus in contextual memory given that, in all previous monkey studies, the hippocampal lesions included cortical areas adjacent to the hippocampus. Thus, it remains possible that the impairment in contextual memory may have resulted from residual damage to the adjacent cortex, especially given that selective damage to parahippocampal areas (TH/TF) impairs contextual memory. Therefore, this study examined whether selective neonatal hippocampal lesions in monkeys (Macaca mulatta), which left the surrounding cortical areas intact, affect contextual learning and memory compared to controls. Monkeys were tested with an automated touch-screen apparatus so that stimuli and contextual cues could be manipulated independently of one another. The data suggests that animals with neonatal hippocampal lesions have sparing of function in regards to contextual learning and memory when (1) contextual information is irrelevant or relevant for good discrimination performance, (2) transferring a contextual rule to new discriminations, (3) discriminating between stimuli presented in previously associated contexts, and (4) on an incidental recognition task with context manipulations. These findings are at odds with studies examining contextual learning and memory in monkeys with selective adult hippocampal lesions, and those with non-selective neonatal hippocampal lesions, which have demonstrated impairment in contextual learning and memory. Therefore, the sparing of function seen in this study may be due to the early nature of the damage and the plastic nature of the infant brain, as well as the intact medial temporal lobe cortical areas as a result of the lesion methodology. Specifically, by removing the hippocampus early in life, before it has begun to function, the parahippocampal (TH/TF) and perirhinal cortices may be able to support context processing throughout life.

Table of Contents

Introduction........................................................................... 1

Method................................................................................ 15

Experiment 1: 24-hrs Concurrent Discrimination........................ 22

Experiment 2: Context Independent CD.................................... 25

Experiment 3: Context Dependent CD...................................... 28

Experiment 4: Context Dependent CD Rule Transfer................... 32

Experiment 5: Context Dependent and Repeating CD................. 36

Experiment 6: Context Visual Paired Comparison....................... 42

Lesion Extent and Correlation with Behavioral Measures............. 46

Discussion............................................................................ 49

References............................................................................90

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