第一章 神经经济学的诞生：从理想到实证 Chapter 1: The Emergence of Neuroeconomics: From Ideal to Empirical

第一章 神经经济学的诞生：从理想到实证

1.1 导论：经济学的理性之梦

当我们审视人类思想史时，会发现一个引人深思的现象：几乎所有试图解释人类行为的学科，最终都必须回答一个根本性问题——人类究竟能否理性地思考和行动？经济学作为研究人类选择行为的学科，对此问题的回答尤为关键，因为它直接决定了经济学理论的基本假设和分析框架。从某种意义上说，经济学对“理性”的理解，不仅塑造了这门学科自身的命运，更深刻地影响了我们对人类本性的认知。

神经经济学的兴起，正是对这一根本性问题的当代回应。这一新兴交叉学科试图将神经科学的实证方法与经济学的理论框架相结合，通过直接观测大脑在决策过程中的活动，来揭示人类选择行为的生物学基础。这一学科的出现，标志着人类对自身理性能力的研究进入了一个全新的阶段——从纯粹的理论推演和抽象建模，转向了对真实神经机制的直接探索。

本章的任务，是对神经经济学的学术谱系进行系统追溯。我们将从古典经济学的“理性人假设”出发，考察这一假设如何成为经济学的理论基石，又如何遭受来自行为经济学的批判性挑战。随后，我们将探讨认知神经科学带来的技术革命，特别是功能性磁共振成像（fMRI）、正电子发射断层扫描（PET）等脑成像技术的突破性进展，如何使直接观测大脑决策过程成为可能。在此基础上，我们将深入分析普洛特金（Charles Plott）和卡默勒（Colin Camerer）等人如何为这一领域奠定方法论基础，最终阐明神经经济学为何不是一个简单的学科嫁接，而是一种认识论上的范式转换——它要求我们重新定义“偏好”、“理性”和“价值”等核心概念，从而根本上改变我们理解人类决策的方式。

In examining the intellectual history of human thought, we encounter a profound question that nearly every discipline seeking to explain human behavior must ultimately address: Can human beings truly think and act rationally? Economics, as the discipline concerned with the study of human choice behavior, provides a particularly critical answer to this fundamental question, as it directly determines the basic assumptions and analytical frameworks of economic theory. In a certain sense, economics' understanding of "rationality" has not only shaped the destiny of this discipline itself but has also profoundly influenced our comprehension of human nature.

The emergence of neuroeconomics represents a contemporary response to this fundamental question. This emerging interdisciplinary field seeks to integrate the empirical methods of neuroscience with the theoretical frameworks of economics, utilizing direct observation of brain activity during decision-making processes to uncover the biological foundations of human choice behavior. The advent of this discipline marks a new era in humanity's investigation of its own rational capacities—one that transitions from purely theoretical deduction and abstract modeling toward direct exploration of authentic neural mechanisms.

The task of this chapter is to systematically trace the intellectual lineage of neuroeconomics. We begin with the "rational man assumption" of classical economics, examining how this assumption became the theoretical cornerstone of economics and subsequently faced critical challenges from behavioral economics. Next, we explore the technological revolution brought about by cognitive neuroscience, particularly the breakthrough advances in brain imaging technologies such as functional magnetic resonance imaging (fMRI) and positron emission tomography (PET), which have made direct observation of brain decision-making processes possible. Building upon this foundation, we analyze how pioneers such as Charles Plott and Colin Camerer established the methodological foundations for this field, ultimately elucidating why neuroeconomics is not merely a simple interdisciplinary grafting but rather an epistemological paradigm shift—one that demands the redefinition of core concepts including "preference," "rationality," and "value," thereby fundamentally transforming our understanding of human decision-making.

1.2 古典经济学的理性人假设：完美的理论乌托邦

1.2.1 亚当·斯密与启蒙时代的经济理性主义

要理解理性人假设在经济学中的核心地位，我们必须回溯到经济学的思想源头。1776年，亚当·斯密（Adam Smith）在《国富论》（*An Inquiry into the Nature and Causes of the Wealth of Nations*）中提出了被后世视为经济学开山之作的经典论述。在这部划时代的著作中，斯密提出了“看不见的手”这一隐喻，描述了个体追求私利如何能够在市场机制的作用下转化为社会整体的福祉。在斯密看来，尽管每个人“所盘算的也只是他自己的利益”，但在他“追求自身的利益”时，他“被一只看不见的手引导着去促进并非他本意要促进的社会利益”。这一洞见构成了古典自由主义经济学的哲学基础，也奠定了理性人假设的核心地位。

然而，值得注意的是，斯密本人对人类理性的看法远比后世教条化的理解更为复杂和审慎。在其早期著作《道德情感论》（*The Theory of Moral Sentiments*, 1759）中，斯密深入探讨了人类的道德情感、同情心和社会情感对经济行为的调节作用。他认识到，人类行为并非纯粹受自利动机驱动，公正旁观者的内化、道德情感的限制以及社会规范的影响，都在塑造人类行为方面发挥着重要作用。这种对人类复杂性的深刻洞察，与后来被简化的“理性经济人”形象形成了鲜明对比。斯密晚年在修订《道德情感论》时，甚至更加重视人类情感和道德在社会经济生活中的作用，这表明他从未将人类简单地还原为纯粹理性的计算机器。

尽管如此，斯密在《国富论》中确立的自利行为逻辑，为后来的理性人假设提供了基本的理论框架。这一框架的逻辑是：在一个运作良好的市场中，追求自身利益最大化的个体，通过价格机制的调节，能够实现资源的有效配置。只要市场是竞争性的、信息是充分的，个体追求私利的行为就自动趋向于社会最优。这一逻辑在后来的新古典经济学中得到了更为精致和形式化的表达，成为现代主流经济学的理论基础。

To understand the central position of the rational man assumption in economics, we must trace back to the intellectual origins of the discipline. In 1776, Adam Smith proposed what subsequent generations would regard as the foundational work of economics in *An Inquiry into the Nature and Causes of the Wealth of Nations*. In this seminal work, Smith introduced the metaphor of the "invisible hand," describing how individuals pursuing self-interest could, through the functioning of market mechanisms, transform their actions into overall social welfare. In Smith's view, although everyone "only thinks of his own gain," when he "pursues his own interest," he "is led by an invisible hand to promote an end which was no part of his intention"—namely, the social interest. This insight constituted the philosophical foundation of classical liberal economics and established the core position of the rational man assumption.

However, it is noteworthy that Smith's own view of human rationality was far more complex and nuanced than the later doctrinal simplifications would suggest. In his earlier work *The Theory of Moral Sentiments* (1759), Smith deeply explored how human moral sentiments, sympathy, and social emotions regulate economic behavior. He recognized that human behavior was not purely driven by self-interest motives; the internalization of the impartial spectator, the constraints of moral sentiments, and the influence of social norms all played significant roles in shaping human behavior. This profound insight into human complexity stands in sharp contrast to the later simplified image of the "rational economic man." In his later revisions of *The Theory of Moral Sentiments*, Smith increasingly emphasized the role of human emotions and morality in socio-economic life, indicating that he never reduced humans to purely rational calculating machines.

Nevertheless, the logic of self-interested behavior established by Smith in *The Wealth of Nations* provided the basic theoretical framework for the later rational man assumption. The logic of this framework is as follows: in a well-functioning market, individuals pursuing their own interests can achieve efficient resource allocation through the regulation of price mechanisms. As long as markets are competitive and information is sufficient, individual pursuit of self-interest automatically tends toward the social optimum. This logic received more refined and formalized expression in later neoclassical economics, becoming the theoretical foundation of modern mainstream economics.

1.2.2 理性选择理论的形式化与公理化

如果说亚当·斯密为理性人假设提供了思想萌芽，那么20世纪中期的理性选择理论则将这一假设发展成为一个具有严格数学基础的公理化体系。这一发展过程的标志性事件，是von Neumann和Morgenstern于1944年出版的《博弈论与经济行为》（*Theory of Games and Economic Behavior*）以及阿罗（Kenneth Arrow）和德布鲁（Gérard Debreu）在1950年代对一般均衡理论的数学表述。

von Neumann和Morgenstern的贡献在于，他们将个体的偏好关系用严格的公理加以形式化。这些公理包括完备性（任何两个可选方案都可以比较）、传递性（如果A优于B，B优于C，则A优于C）、连续性（如果A优于B，则存在一个概率阈值使得混合了A和C的彩票优于确定的B）以及独立性（如果A优于B，则在A和C的混合彩票与B和C的混合彩票之间，前者仍然更优）。在这些公理的基础上，他们证明了效用函数的存在性定理：只要个体的偏好满足上述公理，就可以用一个数值函数来代表其偏好，该函数的最大化就等价于理性的选择行为。

这一公理化进路的深远意义在于，它将经济学的核心假设从模糊的哲学断言转化为精确的数学条件。理性不再是一种笼统的道德要求或心理假设，而是一组可以用经验检验的技术性条件。这种形式化使得经济学能够借用数学的严谨性来证明各种理论命题，也使得经济学的预测可以被精确地表述为可检验的假说。从方法论的角度看，这种公理化进路还具有一个重要特征：它将偏好视为“给定”的外生变量，不对偏好的起源做任何因果性解释。经济学只关心偏好与选择之间的一致性关系，而不追问偏好本身是如何形成和变化的。

这一方法论立场在理性选择理论的后续发展中得到了进一步强化。保罗·萨缪尔森（Paul Samuelson）在1938年提出的“显示性偏好理论”（Revealed Preference Theory）就是典型代表。萨缪尔森认为，经济学的任务不是去推断消费者“真正”的内在偏好是什么，而是从观察到的选择行为中“显示”出偏好。如果一个人的选择行为满足某些一致性条件（如弱公理和强公理），就可以说他是一个“理性”的消费者，而不需要对其心理状态做任何假设。这种方法论上的操作主义立场，极大地简化了经济学的分析，也使经济学能够回避对偏好本质的哲学追问。

If Adam Smith provided the intellectual seeds for the rational man assumption, then the formalization and axiomatization of rational choice theory in the mid-twentieth century transformed this assumption into a rigorous mathematical system. The landmark events in this developmental process were von Neumann and Morgenstern's 1944 publication of *Theory of Games and Economic Behavior* and the mathematical formulation of general equilibrium theory by