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Published: 2018-12-20 09:47 | Updated: 2018-12-20 10:02

Learning from rewards is related to dopamine receptor density

New research from Karolinska Institutet shows that our ability to learn from previously rewarded actions is directly related to the dopamine receptor density in the dorsal striatum, a central structure in the dopaminergic circuit in the brain. The study is published in the scientific journal PNAS.

Lieke de Boer, photo: Maria YohuangThe brain’s dopaminergic pathways are thought to enable us to approach rewards and stay away from punishments. During learning, dopaminergic reward prediction errors are thought to reinforce previously rewarded actions, so they become easier to repeat. This dopaminergic activity could lead to a systematic bias by which rewarded actions are more readily learned than rewarded inactions. In the current study, doctoral student Lieke De Boer and colleagues at the Department of Neurobiology, Care Sciences and Society present findings about the organisation of dopamine receptors in the human brain and its relation to learning.

What are the most important findings of your study?

“We present two important findings. First, dopamine D1 receptors in the cortex, dorsal striatum, and nucleus accumbens provide three distinct sources of variance in the human brain. Second, people learn faster from previously rewarded actions, and the extent to which their learning is accelerated in these situations is dependent on the dopamine receptor density in dorsal striatum, a central structure in the dopaminergic circuit.”

”We are the first to demonstrate this organisation of dopamine D1 receptors in humans. We are also among the first to provide evidence of a direct relationship between dopamine receptor availability and learning from rewards.”

What is the long-term significance of your research?

“These findings provide important basic evidence of dopamine receptors' involvement in reward learning and decision-making and increases our current understanding of the dopaminergic system.”

How did you perform the study?

“We used positron emission tomography (PET) imaging, to detect dopamine D1 receptor availability. Then, we let people perform a simple task where they were instructed to learn to correct action (go or no-go) in response to four different stimuli. They were supposed to learn the correct action from the feedback they received (a reward or a punishment). We showed that people learned faster from "go" responses that were rewarded than any other type of trial, and that the extent to which this is true is related to dopamine receptors in the dorsal striatum.”

The main supervisor of Lieke de Boer is Docent Marc Guitart-Masip, also last author of the current article. The research has been conducted with support from the Swedish Research Council, the Humboldt Research Award, the af Jochnick Foundation, and the Torsten and Ragnar Söderberg Foundations.

Publication

Dorsal striatal dopamine D1 receptor availability predicts an instrumental bias in action learning
Lieke de Boer, Jan Axelsson, Rumana Chowdhury, Katrine Riklund, Raymond Dolan, Lars Nyberg, Lars Bäckman, Marc Guitart-Masip
PNAS, online 18 December 2018, doi: 10.1073/pnas.1816704116