Elliott R, Agnew Z, Deakin J F W
Neuroscience and Psychiatry Unit, Room G907, Stopford Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK.
Eur J Neurosci. 2008 May;27(9):2213-8. doi: 10.1111/j.1460-9568.2008.06202.x.
Functional imaging studies in recent years have confirmed the involvement of orbitofrontal cortex (OFC) in human reward processing and have suggested that OFC responses are context-dependent. A seminal electrophysiological experiment in primates taught animals to associate abstract visual stimuli with differently valuable food rewards. Subsequently, pairs of these learned abstract stimuli were presented and firing of OFC neurons to the medium-value stimulus was measured. OFC firing was shown to depend on the relative value context. In this study, we developed a human analogue of this paradigm and scanned subjects using functional magnetic resonance imaging. The analysis compared neuronal responses to two superficially identical events, which differed only in terms of the preceding context. Medial OFC response to the same perceptual stimulus was greater when the stimulus predicted the more valuable of two rewards than when it predicted the less valuable. Additional responses were observed in other components of reward circuitry, the amygdala and ventral striatum. The central finding is consistent with the primate results and suggests that OFC neurons code relative rather than absolute reward value. Amygdala and striatal involvement in coding reward value is also consistent with recent functional imaging data. By using a simpler and less confounded paradigm than many functional imaging studies, we are able to demonstrate that relative financial reward value per se is coded in distinct subregions of an extended reward and decision-making network.
近年来的功能成像研究证实了眶额皮质（OFC）参与人类的奖赏处理，并表明OFC的反应依赖于情境。在灵长类动物中进行的一项开创性电生理实验，训练动物将抽象视觉刺激与价值不同的食物奖赏联系起来。随后，呈现这些习得的抽象刺激对，并测量OFC神经元对中等价值刺激的放电情况。结果显示，OFC的放电依赖于相对价值情境。在本研究中，我们开发了该范式的人类模拟实验，并使用功能磁共振成像对受试者进行扫描。分析比较了神经元对两个表面上相同的事件的反应，这两个事件仅在前述情境方面有所不同。当刺激预测的是两个奖赏中价值更高的那个时，内侧OFC对相同感知刺激的反应，比它预测价值较低的奖赏时更大。在奖赏回路的其他组成部分，杏仁核和腹侧纹状体中也观察到了额外的反应。核心发现与灵长类动物实验结果一致，表明OFC神经元编码的是相对而非绝对奖赏价值。杏仁核和纹状体参与奖赏价值编码也与最近的功能成像数据一致。通过使用比许多功能成像研究更简单且混淆因素更少的范式，我们能够证明相对金钱奖赏价值本身是在一个扩展的奖赏和决策网络的不同子区域中编码的。
