published_or_final_version / Biological Sciences / Master / Master of Philosophy

He Wu-jing. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 48-57). / Abstracts in English and Chinese. / Abstract --- p.ii / Chinese Abstract (論文摘要) --- p.iv / Acknowledgements --- p.vi / Table of Contents --- p.vii / List of Tables --- p.viii / List of Figures --- p.ix / Chapter Chapter 1 - --- fMRI as a Neuroimaging Method --- p.1 / Chapter Chapter 2 - --- An Review of the Relationship Between Prefrontal Lobes and Memory --- p.6 / Chapter Chapter 3 - --- The Present Study --- p.12 / Chapter Chapter 4 - --- Method --- p.17 / Chapter Chapter 5 - --- Results --- p.25 / Chapter Chapter 6 - --- Discussion --- p.41 / References --- p.48

The information processing approach was used as a basis for studying some brief visual memory processes in reading disabled children. Three aspects of processing were examined, viz. (i) Duration of icon persistence; (ii) Performance under different backward masking conditions; and (iii) Processing of information into a more durable short-term visual memory store. It was found that there were no differences in the duration of icon persistence in reading disabled children, but that these children exhibited marked impairment in performance in the tasks used in the latter two experiments. The reasons for the reading disabled children's poorer performance in these tasks were not apparent. Speculations about the strategies used by these children in approaching the tasks are made. Possible implications and directions for future research are discussed. / Thesis (M.Soc.Sc.)-University of Natal, Durban, 1980.

Different events usually contain similar elements that can contribute to interference during memory encoding and retrieval. The hippocampus (HPC), a structure that is critically involved in some forms of memory, has been hypothesized to reduce interference between memories with overlapping content, thus facilitating correct recall. Pattern separation is one hypothetical process whereby input ambiguity is reduced. Here we test the hypothesis that the HPC and/or dentate gyrus (DG) are important for pattern separation by measuring performance by rats with damage in tasks that require discrimination between visual stimuli that share systematically varying numbers of common elements. Rats with HPC damage were slower to resolve discriminations with minimal degrees of overlap. Lesions of the DG did not affect the ability of rats to deal with overlap, suggesting a dissociation between the HPC and DG. Our results provide partial support for the idea that the HPC contributes to the pattern separation process. / ix, 84 leaves : ill. ; 29 cm.

The hippocampus and non-hippocampal long-term memory systems each have the capacity to learn and express contextual fear memory. How these systems interact during learning and remembering revolves around hippocampal mediated interference, where the hippocampus dominates for both the acquisition and expression of long-term memory. Hippocampal interference during learning can be overcome by modifying learning parameters such that learning is distributed across multiple independent sessions. The standard view of the role of the hippocampus in long-term memory retrieval is that it is temporally limited, where recently acquired memory is dependent on hippocampal function though as a memory ages, dependency is transferred to other memory systems by a process called systems consolidation. Distributed training demonstrates that learning parameters create a memory that is resistant to hippocampal damage. We find little evidence to support temporally based systems consolidation, and present data that supports the view that if the hippocampus is initially involved in learning a memory, it will always be necessary for accurate retrieval of that memory. A critical assessment of the rat literature revealed that initial memory strength, and/or lesion techniques might be responsible for the few studies that report temporally graded retrograde amnesia using contextual fear conditioning. Our experiments designed to directly test these possibilities resulted in flat gradients, providing further evidence that the hippocampus plays a permanent role in long-term memory retrieval. We propose and assess alternatives to the standard model and conclude that a dual store model is most parsimonious within the presented experiments and related literature. Interactions of the hippocampus and non-hippocampal systems take place at the time of learning and remembering, and are persistent over time. / xvi, 161 leaves : ill. (some col.) ; 29 cm

This series of experiments used the multiple learning and memory systems hypothesis of the mammalian nervous system to investigate the possibility that the amygdala, dorsal striatum, and hippocampal systems might, in certain situations, interact to produce behavior in the normal animal. Using variations of the conditioned-cue preference (CCP) task, evidence is presented showing that context-specific information acquired by the hippocampus interferes with acquisition of amygdala-based stimulus-reward learning. It was also demonstrated that there are amygdala-, dorsal striatum-, and hippocampus-based forms of place learning and that cue ambiguity and movement are important factors determining which of these learning and memory systems gain behavioral control in place learning situations. These findings provide evidence for interactions among learning and memory systems and implicate the amygdala and dorsal striatum in some types of non-hippocampal based place learning using distal cues.

The present thesis investigates the effects of lesions to several hypothesized learning and memory systems on the morphine conditioned cue preference on the radial maze. Lesions of the structures thought to be centered to learning systems: the lateral nucleus of amygdala, fornix/fimbria, anterior dorsal striatum and posterior dorsal striatum, were made, In Experiment One, each structure was lesioned separately. Only lesions of the lateral nucleus of amygdala blocked morphine CCP learning. In Experiment Two, rats with combined lesions of fornix/fimbria and dorsal striatum, the lateral nucleus of amygdala and fornix/fimbria, as well as the lateral nucleus of amygdala and dorsal striatum were all impaired on morphine CCP. All of the rats with combined lesions were impaired in this CCP learning. These findings suggest that the lateral nucleus of amygdala is necessary for the morphine CCP. Participation of dorsal striatum or fornix/fimbria is also required. Some hypotheses about the interactions among the structures are discussed.

Memory function was examined in association with sex hormone levels in women. The results of the first study suggest that self-reports of memory problems were especially prevalent among women attending a menopause clinic compared to a nonpatient sample. In the following investigation, women given placebo after undergoing a bilateral oophorectomy showed decreases in memory performance, specifically on a paired-associate learning task, coincident with declines in estrogen levels. Significant improvements were found in estrogen-treated women pre- to postoperatively in the immediate recall of paragraphs, in association with supraphysiological estrogen levels. A final study on naturally-cycling women found a decline in visual memory performance during the menstrual compared to the luteal phase of the cycle. Visual memory scores were positively correlated with progesterone levels whereas paired-associate recall scores were positively associated with estradiol levels during the luteal phase. These results suggest that certain aspects of memory covary with changes in sex steroid levels in some women.

The experiments in this thesis investigated the neuropharmacology of memory in the caudate nucleus, using the conditioned emotional response (CER) with visual and olfactory conditioned stimuli (CS). / In experiment 1, post-training, intrastriatal microinjections of both amphetamine and LY 171555, but not SKF 38393: (1) into the posteroventral area improved memory of a visual, but not an olfactory, CER; (2) into the ventrolateral area improved memory of an olfactory, but not a visual, CER. In experiment 2, sulpiride, but not SCH 23390, blocked the memory improving effect of amphetamine. These findings are consistant with the hypothesis that dopamine D2 receptor stimulation mediates the memory enhancement effect of amphetamine in the neostriatum. / In three experiments on a visual CER, pre-training intrastriatal micro-injections of scopolamine impaired acquisition; post-training micro-injections improved consolidation; and pre-testing micro-injections impaired retrieval. These findings are consistant with the hypothesis that striatal muscarinic receptor stimulation mediates some aspects of acquisition and retrieval of sensory-motor memory, and that blockade of these receptors following training has an effect on memory consolidation similar to that of D2-receptor stimulation. / In experiment 6, destruction of the dopaminergic nigrostriatal neurons abolished the memory improving effect of intrastriatal post-training micro-injections of scopolamine and AFDX-384, a specific muscarinic M2 antagonist. These results suggest that the post-training memory improvement produced by muscarinic blockade may be mediated by an M2 receptor, known to be located on dopaminergic nigro-striatal terminals.

The experiments reported in the present dissertation investigated the contribution of the mammillary region to several classes of learning and memory: spatial memory, nonspatial memory, and conditioned aversion learning. It was demonstrated that such lesions impair performance on tasks that require memory for spatial information but that the deficit depends on both the amount of damage within the region as well as the degree of difficulty of the task. A dissociation in the effect of such lesions on performance of comparable spatial and nonspatial memory tasks was shown. In contrast to the severe deficits observed on spatial memory tasks, the acquisition and retention of a complex nonspatial memory task was not impaired after extensive damage to the mammillary region. Such lesions also did not impair performance on two conditioned aversion tasks. These experiments suggest that the mammillary region may be selectively involved in spatial learning and memory. The relevance of these findings to Korsakoff's syndrome is discussed.