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Title:Hippocampal modulation of cingulate cortex and limbic thalamus during learning
Author(s):Kang, Eunjoo
Doctoral Committee Chair(s):Gabriel, Michael
Department / Program:Psychology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Biology, Neuroscience
Psychology, Psychobiology
Abstract:A characteristic of the cingulo-thalamic or the subicular thalamic pathway had been investigated during the discriminative avoidance conditioning in which a CR of stepping in an activity wheel prevents a footshock 5 sec. after an auditory CS+. Enhanced neuronal discharges in the mediodorsal (MDN) and the anterior ventral (AVN) thalamic nuclei were found in rabbits with the combined lesions of posterior cingulate cortex and subiculum in Experiment 1 as after the separate lesions in a previous study (Gabriel et al, 1987). The frequency of CR was also greater in rabbits with the combined lesions during early training. This result suggests that both cingular and subicular input limits the firing of thalamic neurons.
Experiment 2 tested the hypothesis that hippocampal lesions will mimic the effects of subicular lesions. However, the hippocampal lesions enhanced the unit activity in MDN and posterior cingulate cortex (Area 29c/d and Area 29b) but not in AVN or anterior cingulate cortex. The hippocampal lesions did not increase CR-frequency during acquisition, extinction or during reacquisition. These results suggested a suppressive modulation by hippocampal efferents on several limbic structures and a functional independence of subiculum and hippocampus.
In Experiment 3, neuronal activity in the hippocampus, AVN, and posterior cingulate cortex in the well trained rabbits were recorded after temporary hippocampal disruption by medial septal injections of the local anesthetic(Tetracaine:TH) or GAB$\sb{\rm A}$ agonist (muscimol: MUS). The CS evoked discharges in CA3, CA1, and DG were attenuated and the theta-like, sinusoidal macropotentials were altered following either TH or MUS injection. Spontaneous unit activity of CA3 and AVN were also reduced as was the incidence of CR. These findings suggest that disturbing the function of the hippocampus has devastating effects on the performance of the active avoidance task in rabbits in comparison to permanent lesions in the hippocampus.
These findings indicate that the hippocampal modulation is limiting or suppressive on the limbic thalamus and the limbic cortex and that the interaction between the hippocampus and other limbic structures is involved in the performance of the active avoidance task.
Issue Date:1995
Rights Information:Copyright 1995 Kang, Eunjoo
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9543619
OCLC Identifier:(UMI)AAI9543619

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