Neural correlates of frustration and reversal learning, and the impact of the serotonin transporter polymorphism

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Embargoed until 2015-02-28
Copyright: Ng, Pamela
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Abstract
This dissertation investigated the neural basis of reversal learning and frustration, and the impact of the serotonin transporter polymorphism on these neural mechanisms. Reversal learning involves the ability to flexibly adjust behavior to changes in reinforcement (i.e. the ability to avoid frustration). There were 4 fMRI studies of healthy adults in this thesis. The first adapted a previously developed reversal learning (RL) paradigm. Critically, this adaptation allowed separation at the neural level of responses associated with processing reinforcement expectation relative to feedback. Previous studies have implicated areas including dorsomedial prefrontal cortex (dmPFC), dorsal anterior cingulate (dACC) and dorsolateral prefrontal cortex (dlPFC) in RL. However, RL involves multiple stages, which were not separately examined in these studies. The first study sought to functionally dissect the neural substrates of the different stages of RL. The second study introduced a frustrative non-reward phase where expected rewards were omitted. Frustration is experienced when an individual performs an action in expectation of a reward but does not actually receive that reward. Individuals with deficits in reversal learning are thus more likely to fail to achieve their goals, and are at increased risk for frustration. These two studies tested the hypothesis that the neural circuitry underlying RL and frustration share common substrates. Studies 3 and 4 investigated the impact of the serotonin transporter polymorphism (5-HTTLPR) on neural processing during RL and frustration. Previous findings have suggested that 5-HT is critical for both flexible responding and frustration, but surprisingly little work has addressed how these systems are related or interact. The studies indicated that learning to avoid frustration activates brain regions implicated in reversal learning (dACC, dmPFC, dlPC), and also demonstrated a novel role for the posterior cingulate cortex (PCC). In non-frustrating conditions, individuals with the short allele of the 5-HTT exhibited decreased activity in response to punishment information. However, under frustrating conditions, the short allele exerted its strongest effects on neural responding in dmPFC and PCC. Taken together, these studies explicated the neural circuitry underlying reversal learning and frustration, and provide support for the role of the serotonin transporter in modulating these regions under provocation.
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Author(s)
Ng, Pamela
Supervisor(s)
Mitchell, Phillip
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Publication Year
2013
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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