Abstract
In order to investigate roles of dopamine receptor subtypes in reward-based learning, we examined choice behavior of dopamine D1 and D2 receptor-knockout (D1R-KO and D2R-KO, respectively) mice in an instrumental learning task with progressively increasing reversal frequency and a dynamic two-armed bandit task. Performance of D2R-KO mice was progressively impaired in the former as the frequency of reversal increased and profoundly impaired in the latter even with prolonged training, whereas D1R-KO mice showed relatively minor performance deficits. Choice behavior in the dynamic two-armed bandit task was well explained by a hybrid model including win-stay-lose-switch and reinforcement learning terms. A model-based analysis revealed increased win-stay, but impaired value updating and decreased value-dependent action selection in D2R-KO mice, which were detrimental to maximizing rewards in the dynamic two-armed bandit task. These results suggest an important role of dopamine D2 receptors in learning from past choice outcomes for rapid adjustment of choice behavior in a dynamic and uncertain environment.
Highlights
There has been a large progress in understanding roles of dopamine in reward processing over the last two decades
All animals learned to choose correct target in the simple instrumental learning task, performance of D2R-KO mice was impaired as stability and certainty of action-reward contingency decreased, whereas performance deficits of D1R-KO were relatively small
A model-based analysis indicated increased www.frontiersin.org win-stay tendency, but impaired value updating and decreased value-dependent action selection in D2R-KO mice, which was detrimental to making optimal choices in the TAB task
Summary
There has been a large progress in understanding roles of dopamine in reward processing over the last two decades. A large body of subsequent studies employing the RL theory have yielded results that further support the role of dopamine in updating value functions according to RPE (Daw and Doya, 2006; Dayan and Niv, 2008; Kable and Glimcher, 2009; Niv and Montague, 2009; Lee et al, 2012). This line of research emphasizes an essential role of dopamine in learning to choose optimally for maximizing rewards. The extent and nature of dopamine roles in RL are still under debate
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