Kalenscher Tobias, Tobler Philippe N, Huijbers Willem, Daselaar Sander M, Pennartz Cyriel M A
Department of Cognitive and Systems Neuroscience, Swammerdam Institute for Life Sciences, University of Amsterdam Amsterdam, Netherlands.
Front Hum Neurosci. 2010 Jun 9;4. doi: 10.3389/fnhum.2010.00049. eCollection 2010.
It is often assumed that decisions are made by rank-ordering and thus comparing the available choice options based on their subjective values. Rank-ordering requires that the alternatives' subjective values are mentally represented at least on an ordinal scale. Because one alternative cannot be at the same time better and worse than another alternative, choices should satisfy transitivity (if alternative A is preferred over B, and B is preferred over C, A should be preferred over C). Yet, individuals often demonstrate striking violations of transitivity (preferring C over A). We used functional magnetic resonance imaging to study the neural correlates of intransitive choices between gambles varying in magnitude and probability of financial gains. Behavioral intransitivities were common. They occurred because participants did not evaluate the gambles independently, but in comparison with the alternative gamble presented. Neural value signals in prefrontal and parietal cortex were not ordinal-scaled and transitive, but reflected fluctuations in the gambles' local, pairing-dependent preference-ranks. Detailed behavioral analysis of gamble preferences showed that, depending on the difference in the offered gambles' attributes, participants gave variable priority to magnitude or probability and thus shifted between preferring richer or safer gambles. The variable, context-dependent priority given to magnitude and probability was tracked by insula (magnitude) and posterior cingulate (probability). Their activation-balance may reflect the individual decision rules leading to intransitivities. Thus, the phenomenon of intransitivity is reflected in the organization of the neural systems involved in risky decision-making.
人们通常认为，决策是通过对可用选择选项进行排序并根据其主观价值进行比较来做出的。排序要求至少在序数尺度上对备选方案的主观价值进行心理表征。由于一个备选方案不可能同时比另一个备选方案更好或更差，选择应该满足传递性（如果备选方案A优于B，且B优于C，那么A应该优于C）。然而，个体常常表现出明显的传递性违背（偏好C而非A）。我们使用功能磁共振成像来研究在金融收益的大小和概率不同的赌博之间进行非传递性选择的神经关联。行为上的非传递性很常见。它们之所以出现，是因为参与者并非独立评估赌博，而是与呈现的另一个赌博进行比较。前额叶和顶叶皮质中的神经价值信号并非按序数尺度且具有传递性，而是反映了赌博的局部、依赖配对的偏好等级的波动。对赌博偏好的详细行为分析表明，根据所提供赌博属性的差异，参与者对大小或概率给予了不同的优先级，从而在偏好更丰厚或更安全的赌博之间转换。脑岛（大小）和后扣带回（概率）追踪了给予大小和概率的可变的、依赖情境的优先级。它们的激活平衡可能反映了导致非传递性的个体决策规则。因此，非传递性现象反映在参与风险决策的神经系统的组织中。
