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|Title:||Behavioral and Adrenocortical Responses of Rats with Fornix Lesions to Changes in Environmental Stimulation|
|Advisor:||Black, A. H.|
|Abstract:||<p>The behavior of animals with hippocampal damage differs from that of normal animals across a variety of behavioral tasks. However, the indices of learning and performance used to assess the effects of hippocampal damage are limited in information content, and are easily subsumed by several current theories of hippocampal funct ion. The approach taken in the present series of experiments was to utilize tasks that consistently result in behavioral deficits in animals with hippocampal damage, but to increase the amount of information. The experiments analyzed the response of rats with total fornix lesions to the transition from acquisition to extinction of a response. Detailed observations of the behavior and measurement of corticosterone levels allowed a more complete picture of the hippocampal deficit to emerge.</p> <p>Experiment 1 examined acquisition and extinction of an operant lever press response in a standard operant chamber. Fornix lesioned rats made fewer responses during acquisition and had increased resistance to extinction. Detailed analysis revealed many other differences in the behavior of control and lesioned rats. Control rats reacted to the transition to extinction with decreased frequency of bouts of food related behaviors, increased bout durations of all behaviors, changed topography of lever presses from acquisition type presses to biting responses, changed sequential organization of behaviors, and behaviors labelled as emotional. Control rats also responded to the transition with increased plasma corticosterone levels, an increase that was negatively correlated with response burst duration and amount of biting, and positively related to the maintenance of acquisition responses. Fornix lesioned rats exhibited more random behavioral organization, in both acquisition and extinction. Following the transitiun to extinction, lesioned rats did not exhibit the behavioral flexihility, corticosterone increases, or behaviorcorticosterone relationships exhibited by control rats.</p> <p>Experiment 2 maintained the same task requirements but in a large, enriched environrnent. Less efficient behavioral organization resulted in lesioned rats again receiving fewer reinforcements during acquisition. Both grous extinguishnd faster tn the large enriched environment than in Experiment 1, but lesioned rats maintained food related behaviors longer than controls. Lesioned rats exhibited only acquisition type responses interspersed with short trips away from the lever and food cup. Controls exhibted two modes of response interspersed with short. ion trips away. During trips away, the groups differed in their interactions with objects in the environment in terms of frequency, duration, intensity and temporal and sequential organizations.</p> <p>Experiment 3 examined exploratory behavior patterns during initial exposure to the experimental environment of Experiment 2. The groups again differed in frequency, quality and organization of their interactions with objects in the environment. Control rat exploratory patterns were similar to those during extinction, but lesioned rat patterns differed.</p> <p>Experiment 4 examined the response of lesioned and control rats to environmental change in a simple appetitive consummatory task. After being allowed to eat, the rat's consummatory response was blocked while 'the cues controlling behavior were maintained. The groups differed in the frequency, duration and organization of their behavior. Controls responded to the change with increased corticosterone and altered behavioral strategies while lesioned rats showed neither.</p> <p>Experiments 4, 5 and 6 examined alternative explanations of the differences in corticosterone response profiles of control and lesioned rats during acquisition and extinction. These differences appear not to have resulted from 1) differences in conditioning to the sampling procedure, 2) a general attenuation of responsiveness in lesioned rats, or 3) differences in response to the novel aspects of the testing environment.</p> <p>The detailed analysis of behavior suggests that fornix lesioned rats differ from controls in the organization of behavior and in response to changes in environmental demands. The results are used to address contradictory issues in current theories of hippocampal function.</p>|
|Description:||<p>" First two papers came out black while the other ones are fine".</p>|
|Appears in Collections:||Open Access Dissertations and Theses|
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