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Title: Learning and decision making in fronto-striatal syndromes
Author: Chase, H. W. N.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2008
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Section I focuses on behavioural performance of a large group of patients with frontal lobe lesions. Lesions encroaching on the orbitofrontal cortex (OFC) were shown to disrupt two tests of discrimination learning performance. I describe the critical role of other regions (right inferior frontal gyrus and dorsolateral prefrontal cortex) to self-ordered spatial working memory performance. Section 2 describes tests of a number of assumptions of Frank’s model in healthy subjects. Using EEG, I investigated a waveform called the feedback-related negativity, which is thought to represent negative prediction errors, evoked during a probabilistic reversal learning task. I performed a behavioural study of probabilistic reversal learning, altering feedback valence, to further support the idea that a prediction error system mediates performance on this task. I performed a study using an adaptation of the probabilistic selection task, which has provided key evidence in support of Frank’s model, using a devaluation procedure via instructions. Subjects show a devaluation effect, demonstrating that performance could be influenced by an explicit mechanism. These data challenge notions that the task requires the strengthening of procedural stimulus-response associations. In Section 3 I investigate predictions of Frank’s model in a relevant neuropsychiatric disorder, depression. Following a prior study of depressed patients on a probabilistic reversal learning task, I investigated the prediction that there would be facilitated avoidance learning compared to approach learning in the patient group on the probabilistic selection task. No evidence supporting this prediction was found. I demonstrate that depressed patients exhibit improved performance on the motivated reaction time task. These data indicate that depression is not accompanied by non-specific performance deficits. Modifications to Frank’s model that might account for these data are discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available