Neural Mechanisms of Reward Processing

描述（由候选人提供）：当奖励只有在延迟一段时间后才被预期时，其现值是通过相对于延迟时间的价值进行贴现来合理确定的。在人类和动物身上进行的旨在确定这种时间折扣函数性质的实验发现，时间在短期内比在长期内更有价值：这种现象被称为双曲线时间折扣。 双曲贴现的确切性质仍然存在激烈争论，没有经验数据能够清楚地区分替代假设。 在这个建议中，一系列的功能性MRI实验被开发出来，以区分两个最流行的理论，双曲贴现如何从大脑功能中产生。 我们测试了几个假设，受试者在不同延迟的不同幅度的奖励结果之间做出选择。 我们的实验采用自然奖励（果汁）和金钱奖励来确定相关的大脑结构是否在奖励模式中普遍存在。 除了这项实验工作之外，我们还将使用强化学习方法进行计算研究，以确定人们在时间上双曲线贴现的原因是否存在规范性原因。

DESCRIPTION (provided by candidate): When rewards are expected only after some delay, their present value is reasonably determined by discounting their worth relative to the length of the delay. Experiments aimed at determining the nature of such time discount functions in people and animals have found that time is valued significantly more in the near-term than in the long-term: a phenomenon known as hyperbolic time discounting. The exact nature of hyperbolic discounting remains hotly debated, with no empirical data able to clearly distinguish between alternative hypotheses. In this proposal, a series of functional MRI experiments are developed to distinguish between two of the most popular theories for how hyperbolic discounting arises from brain function. We test several hypotheses as subjects make choices between rewarding outcomes of differing magnitudes at different delays. Our experiments employ both natural rewards (fruit juice) and monetary rewards to determine whether the associated brain structures generalize across reward modalities. In addition to this experimental work, we will conduct computational research using reinforcement learning methods to determine whether there are normative reasons for why people discount hyperbolically through time.