Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge CB2 3DY, United Kingdom.
Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge CB2 3DY, United Kingdom
J Neurosci. 2021 Mar 31;41(13):3000-3013. doi: 10.1523/JNEUROSCI.1555-20.2020. Epub 2021 Feb 10.
Rewarding choice options typically contain multiple components, but neural signals in single brain voxels are scalar and primarily vary up or down. In a previous study, we had designed reward bundles that contained the same two milkshakes with independently set amounts; we had used psychophysics and rigorous economic concepts to estimate two-dimensional choice indifference curves (ICs) that represented revealed stochastic preferences for these bundles in a systematic, integrated manner. All bundles on the same ICs were equally revealed preferred (and thus had same utility, as inferred from choice indifference); bundles on higher ICs (higher utility) were preferred to bundles on lower ICs (lower utility). In the current study, we used the established behavior for testing with functional magnetic resonance imaging (fMRI). We now demonstrate neural responses in reward-related brain structures of human female and male participants, including striatum, midbrain, and medial orbitofrontal cortex (mid-OFC) that followed the characteristic pattern of ICs: similar responses along ICs (same utility despite different bundle composition), but monotonic change across ICs (different utility). Thus, these brain structures integrated multiple reward components into a scalar signal, well beyond the known subjective value coding of single-component rewards. Rewards have several components, like the taste and size of an apple, but it is unclear how each component contributes to the overall value of the reward. While choice indifference curves (ICs) of economic theory provide behavioral approaches to this question, it is unclear whether brain responses capture the preference and utility integrated from multiple components. We report activations in striatum, midbrain, and orbitofrontal cortex (OFC) that follow choice ICs representing behavioral preferences over and above variations of individual reward components. In addition, the concept-driven approach encourages future studies on natural, multicomponent rewards that are prone to irrational choice of normal and brain-damaged individuals.
奖励选择选项通常包含多个组成部分，但单个脑体素中的神经信号是标量的，主要表现为上下变化。在之前的一项研究中，我们设计了包含相同两种奶昔的奖励套餐，这些奶昔的份量是独立设定的；我们使用心理物理学和严格的经济概念来估计二维选择无差异曲线（IC），这些曲线以系统的、综合的方式代表了对这些套餐的随机偏好。同一 IC 上的所有套餐都是同等偏好的（因此，根据选择无差异推断，它们具有相同的效用）；效用较高的 IC 上的套餐（更高的效用）比效用较低的 IC 上的套餐（更低的效用）更受偏好。在当前的研究中，我们使用已建立的行为来进行功能磁共振成像（fMRI）测试。我们现在展示了人类女性和男性参与者的奖励相关大脑结构的神经反应，包括纹状体、中脑和内侧眶额皮层（mid-OFC），这些反应遵循 IC 特征模式：IC 上的相似反应（尽管套餐组成不同，但具有相同的效用），但在 IC 上的单调变化（不同的效用）。因此，这些大脑结构将多个奖励组成部分整合到一个标量信号中，远远超出了单个奖励成分的已知主观价值编码。奖励有几个组成部分，比如苹果的味道和大小，但每个组成部分如何贡献奖励的整体价值还不清楚。虽然经济理论的选择无差异曲线（IC）提供了一种解决这个问题的行为方法，但还不清楚大脑反应是否捕捉到了来自多个组成部分的偏好和效用的综合。我们报告了纹状体、中脑和眶额皮层（OFC）的激活，这些激活遵循代表行为偏好的选择 IC，超过了单个奖励成分的变化。此外，概念驱动的方法鼓励未来对正常人和大脑损伤个体容易产生非理性选择的自然、多成分奖励进行研究。
