McClure Samuel M, Ericson Keith M, Laibson David I, Loewenstein George, Cohen Jonathan D
Center for the Study of Brain, Mind, and Behavior and Department of Psychology, Princeton University, Princeton, New Jersey 08540, USA.
J Neurosci. 2007 May 23;27(21):5796-804. doi: 10.1523/JNEUROSCI.4246-06.2007.
Previous research, involving monetary rewards, found that limbic reward-related areas show greater activity when an intertemporal choice includes an immediate reward than when the options include only delayed rewards. In contrast, the lateral prefrontal and parietal cortex (areas commonly associated with deliberative cognitive processes, including future planning) respond to intertemporal choices in general but do not exhibit sensitivity to immediacy (McClure et al., 2004). The current experiments extend these findings to primary rewards (fruit juice or water) and time delays of minutes instead of weeks. Thirsty subjects choose between small volumes of drinks delivered at precise times during the experiment (e.g., 2 ml now vs 3 ml in 5 min). Consistent with previous findings, limbic activation was greater for choices between an immediate reward and a delayed reward than for choices between two delayed rewards, whereas the lateral prefrontal cortex and posterior parietal cortex responded similarly whether choices were between an immediate and a delayed reward or between two delayed rewards. Moreover, relative activation of the two sets of brain regions predicts actual choice behavior. A second experiment finds that when the delivery of all rewards is offset by 10 min (so that the earliest available juice reward in any choice is 10 min), no differential activity is observed in limbic reward-related areas for choices involving the earliest versus only more delayed rewards. We discuss implications of this finding for differences between primary and secondary rewards.
先前涉及金钱奖励的研究发现，当跨期选择包含即时奖励时，与边缘系统奖励相关的区域比选项仅包含延迟奖励时表现出更强的活动。相比之下，外侧前额叶和顶叶皮质（通常与深思熟虑的认知过程相关的区域，包括未来规划）一般会对跨期选择做出反应，但对即时性不敏感（麦克卢尔等人，2004年）。当前的实验将这些发现扩展到了初级奖励（果汁或水）以及以分钟而非周为单位的时间延迟。口渴的受试者在实验期间的精确时间提供的少量饮料之间进行选择（例如，现在2毫升 vs 5分钟后3毫升）。与先前的发现一致，与边缘系统激活相比，即时奖励与延迟奖励之间的选择比两个延迟奖励之间的选择更大，而外侧前额叶皮质和顶叶后皮质在选择是即时奖励与延迟奖励之间还是两个延迟奖励之间时反应相似。此外，两组脑区的相对激活程度可预测实际的选择行为。第二个实验发现，当所有奖励的发放都推迟10分钟（这样在任何选择中最早可获得的果汁奖励都是10分钟后）时，在涉及最早奖励与仅更延迟奖励的选择中，边缘系统奖励相关区域未观察到差异活动。我们讨论了这一发现对于初级奖励和次级奖励之间差异的意义。
