The Graduate Forum

an interdisciplinary forum at New York University 

November 18, 2009
Presenter: Robb Ruttledge
Respondent: Sally Newman
How we learn about rewards

The activity of dopamine neurons in our brains are thought to encode an error signal, the difference between the rewards we receive and the rewards we expected to receive. This signal is thought to be used to learn the value of options, values that then guide decision making. In this session of the Forum, I discussed how scientific hypotheses are tested and talked about two attempts I made to test this dopamine hypothesis. First, I measured brain activity using functional MRI as people won and lost money in a gambling task. I used an axiomatic model derived from economic theory to try to falsify the hypothesis for my brain data. It turned out that the signal in the striatum, where the dopamine neurons send connections, satisfies the model and can be an error signal. Second, Parkinson's disease affects the dopamine system and patients take dopamine drugs to treat their symptoms. I tested whether these dopamine drugs affect learning when Parkinson's patients make choices in a learning task, as you would expect if dopamine neurons participate in learning. The dopamine drugs did in fact affect learning exactly as the theory predicts. Both of these results support the hypothesis that dopamine neurons encode some kind of error signal.











New York University

Graduate School of Arts and Sciences