Department of Bio and Brain Engineering, Korean Advanced Institute of Science and Technology, Daejeon, Republic of Korea.
Neuroscience. 2011 Dec 1;197:162-71. doi: 10.1016/j.neuroscience.2011.09.037. Epub 2011 Sep 22.
Dopamine neurons of the ventral midbrain are activated transiently following stimuli that predict future reward. This response has been shown to signal the expected value of future reward, and there is strong evidence that it drives positive reinforcement of stimuli and actions associated with reward in accord with reinforcement learning models. Behavior is also influenced by reward uncertainty, or risk, but it is not known whether the transient response of dopamine neurons is sensitive to reward risk. To investigate this, monkeys were trained to associate distinct visual stimuli with certain or uncertain volumes of juice of nearly the same expected value. In a choice task, monkeys preferred the stimulus predicting an uncertain (risky) reward outcome. In a Pavlovian task, in which the neuronal responses to each stimulus could be measured in isolation, it was found that dopamine neurons were more strongly activated by the stimulus associated with reward risk. Given extensive evidence that dopamine drives reinforcement, these results strongly suggest that dopamine neurons can reinforce risk-seeking behavior (gambling), at least under certain conditions. Risk-seeking behavior has the virtue of promoting exploration and learning, and these results support the hypothesis that dopamine neurons represent the value of exploration.
腹侧被盖区的多巴胺神经元在预测未来奖励的刺激后会短暂激活。这一反应被证明可以信号未来奖励的预期价值，并且有强有力的证据表明，它驱动了与奖励相关的刺激和行为的正强化，与强化学习模型一致。行为也受到奖励不确定性或风险的影响，但尚不清楚多巴胺神经元的短暂反应是否对奖励风险敏感。为了研究这一点，猴子被训练将不同的视觉刺激与具有几乎相同预期价值的特定或不确定量的果汁相关联。在一项选择任务中，猴子更喜欢预测不确定（有风险）奖励结果的刺激。在一个巴甫洛夫任务中，可以单独测量每个刺激的神经元反应，结果发现，与奖励风险相关联的刺激会更强烈地激活多巴胺神经元。鉴于多巴胺驱动强化的广泛证据，这些结果强烈表明，多巴胺神经元至少在某些条件下可以强化风险寻求行为（赌博）。风险寻求行为具有促进探索和学习的优点，这些结果支持了多巴胺神经元代表探索价值的假设。
