Optimal decision making involving reward uncertainty is integral to adaptive goal-directed behavior. In some instances, these decisions are guided by internal representations of reward history, whereas in other situations, external cues inform a decision maker about how likely certain actions are to yield reward. Different regions of the frontal lobe form distributed networks with striatal and amygdalar regions that facilitate different types of risk/reward decision making. The dorsal medial striatum (DMS) is one key output region of the prefrontal cortex, yet there have been few preclinical studies investigating the involvement of the DMS in different forms of risk/reward decision making. The present study addressed this issue, wherein separate groups of male rats were trained on one of two tasks where they chose between a small/certain or a large/risky reward. In a probabilistic discounting task, reward probabilities changed systematically over blocks of trials (100–6.25% or 6.25–100%), requiring rats to use internal representations of reward history to guide choice. Cue-guided decision-making was assessed with a “Blackjack” task, where different auditory cues indicated the odds associated with the large/risky option (50 or 12.5%). Inactivation of the DMS with GABA agonists impaired adjustments in choice biases during probabilistic discounting, resulting in either increases or decreases in risky choice as the probabilities associated with the large/risky reward decreased or increased over a session. In comparison, DMS inactivation increased risky choices on poor-odds trials on the Blackjack task, which was associated with a reduced impact that non-rewarded choices had on subsequent choices. DMS inactivation also impaired performance of an auditory conditional discrimination. These findings highlight a previously uncharacterized role for the DMS in facilitating flexible action selection during multiple forms of risk/reward decision making.

涉及奖励不确定性的最佳决策是适应性目标导向行为的组成部分。在某些情况下，这些决策由奖励历史的内部表示指导，而在其他情况下，外部线索告知决策者某些行动产生奖励的可能性。额叶的不同区域与纹状体和杏仁核区域形成分布式网络，促进不同类型的风险/回报决策。背内侧纹状体 (DMS) 是前额叶皮层的一个关键输出区域，但很少有临床前研究调查 DMS 参与不同形式的风险/回报决策。本研究针对这个问题，其中，不同的雄性大鼠组接受了两项任务之一的训练，他们在小/确定或大/风险奖励之间进行选择。在概率贴现任务中，奖励概率在试验块（100-6.25% 或 6.25-100%）上发生系统性变化，需要大鼠使用奖励历史的内部表征来指导选择。提示引导的决策通过“二十一点”任务进行评估，其中不同的听觉提示表明与大/风险选项相关的几率（50 或 12.5%）。使用 GABA 激动剂使 DMS 失活会损害概率贴现过程中选择偏差的调整，导致风险选择的增加或减少，因为与大/风险奖励相关的概率在一个会话中减少或增加。相比下，DMS 失活增加了对 Blackjack 任务的低赔率试验的风险选择，这与非奖励选择对后续选择的影响降低有关。DMS 失活也损害了听觉条件歧视的表现。这些发现突出了 DMS 在促进多种形式的风险/回报决策过程中灵活行动选择方面的前所未有的作用。