Neural Mediation of Instrumental Learning and Concurrent Discrimination
Smith, David M.
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Permalink
https://hdl.handle.net/2142/82489
Description
Title
Neural Mediation of Instrumental Learning and Concurrent Discrimination
Author(s)
Smith, David M.
Issue Date
2001
Doctoral Committee Chair(s)
Gabriel, Michael
Department of Study
Neuroscience
Discipline
Neuroscience
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Neuroscience
Language
eng
Abstract
The experiments described here examined the neural mediation of instrumental discriminative learning. A great deal is known about the neural circuitry mediating discriminative avoidance learning, wherein rabbits learn to step in an activity wheel in order to avoid a footshock following one tone conditional stimulus (CS+) and they learn to ignore a second tone (CS-) not followed by shock. Previous studies indicated that the amygdala and the cingulothalamic circuit, comprised by the cingulate cortex and the interconnected anterior and medial thalamic nuclei, are critically involved in discriminative avoidance learning. Much less is known about a new, appetitively-motivated discriminative approach task. During discriminative approach learning, rabbits learn to make oral contact with a drinking spout for a water reward following the CS+ and they learn to ignore the CS-. The first objective of these experiments was to identify the circuitry mediating approach learning. Results indicated that the amygdala was critically involved in avoidance learning, but was not needed for approach learning, Consistent with studies of avoidance learning, the cingulothalamic circuit was critically involved in discriminative approach learning, This result indicated a general involvement of the cingulothalairnic circuit in mediating associative learning processes. A second major goal was to investigate hippocampal-cingulothalamic interactions proposed to mediate concurrent discriminative approach and avoidance learning. Training of the two tasks took place in different contexts. Fornix lesions, which disconnect the hippocampal system from the anterior thalamus, impaired concurrent learning and disrupted the context-specific patterning of neuronal activity in the cingulothalamic circuit. This result is consistent with the hypothesis that hippocampal processing modulates cingulothalamic neuronal activity, resulting in a context-specific patterning of neuronal activity which could be used to disambiguate different learning situations.
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