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Title: Roles of dopamine in human memory
Author: Grogan, John Patrick
ISNI:       0000 0004 5916 7702
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2015
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Dopamine is heavily implicated in learning and memory, but the timescale of dopaminergic action in human memory consolidation is not yet clearly mapped, and is the focus of this thesis. A series of behavioural experiments were run with Parkinson's disease (PD) patients to examine the effects of dopaminergic medication withdrawal and administration at different times during reinforcement learning (RL) and episodic memory. Episodic memory was impaired in PD, and dopaminergic medication during learning increased this impairment, while, in contrast, medication overnight (8-24 hours after learning) improved recall at 24 hours. Dopamine during learning also led to a more liberal response bias 24 hours later, for which computational modelling suggested consolidation mechanisms were a plausible explanation. The period between 1 and 7 hours after learning was also explored but no effects of dopamine on RL and episodic memory consolidation were found, in contradiction to animal literature. Surprisingly, in neither experiment did dopamine affect RL behaviour, but participants did develop a bias towards avoiding the negatively reinforced stimuli when a 24 hour gap between learning and recall was introduced. Finally, separate effects of PD and dopamine therapy on working memory were demonstrated, with PD impairing elements that required manipulation of items held in memory, but dopamine affecting phonological storage of items. While the above results all relate to accuracy of performance, there were also unexpected effects of PD and dopamine on reaction times; for example, PD patient responded more quickly than healthy participants in procedural tasks. Altogether, this thesis demonstrates that the timing of dopamine is only one of the factors influencing the way memories are stored over time. Many of the results were unexpected, generating new hypotheses to be tested in future endeavours.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available