Electronic Thesis and Dissertation Repository

Thesis Format



Master of Science




Morton, J. Bruce


Behavioral and neuroimaging studies have identified two valuation systems in the human brain for controlling behavior known as model-free (MF) and model-based (MB). MF is based on immediate evaluation and MB is based on long-term evaluation of the outcome of our decisions. Previous studies suggest that dopamine baseline activity may play an important role in the balance between the two systems and determine how they compete or interact in controlling our actions. The overarching aims of this study is to investigate the impact of levodopa administration on learning from immediate and long-term action consequences, and to dissociate the role of striatal subregions in learning and action selection. Here, an fMRI fast-event related paradigm is designed and validated which enables to computationally model the integration of MF and MB learning and decision making on both behavioral and neural levels.

Summary for Lay Audience

Humans use two strategies for evaluating decisions at hand and choosing the most appropriate action with better payoff. These strategies arise from two separate valuation systems in the brain called model-free (MF) and model-based (MB) systems that often compete, but other times interact with each other to control our behavior. MF behavior involves considering the immediate reward even though the long-term consequences may not be favorable (e.g., unhealthy food consumption). On the other hand, MB behavior involves considering long-term outcome even if an action is not associated with short- term reward such as working hard for distant goals in the future. Dopamine is a neurotransmitter in the brain that is involved in several cognitive functions such as reward-based learning and action selection. Previous studies have shown that administering levodopa, the primary medication for Parkinson’s disease, would increase the dopamine availability in the brain and would bias the choices toward the long-term goals. Here, I have designed and validated a paradigm that is the foundation for a pharmacological manipulation study of dopamine using levodopa combined with functional magnetic resonance imaging (fMRI) to investigate the balance between MF and MB systems and to identify the neural correlates of learning from short-term and long-term action consequences.

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.