Wittmann Marc, Leland David S, Paulus Martin P
Department of Psychiatry, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-9116A, USA.
Exp Brain Res. 2007 Jun;179(4):643-53. doi: 10.1007/s00221-006-0822-y. Epub 2007 Jan 10.
Delay discounting refers to the fact that an immediate reward is valued more than the same reward if it occurs some time in the future. To examine the neural substrates underlying this process, we studied 13 healthy volunteers who repeatedly had to decide between an immediate and parametrically varied delayed hypothetical reward using a delay discounting task during event-related functional magnetic resonance imaging. Subject's preference judgments resulted in different discounting slopes for shorter (<1 year) and for longer (> or =1 year) delays. Neural activation associated with the shorter delays relative to the longer delays was associated with increased activation in the head of the left caudate nucleus and putamen. When individuals selected the delayed relative to the immediate reward, a strong activation was found in bilateral posterior insular cortex. Several brain areas including the left caudate nucleus showed a correlation between the behaviorally determined discounting and brain activation for the contrast of intervals with delays <1 and > or =1 year. These results suggest that (1) the posterior insula, which is a critical component of the decision-making neural network, is involved in delaying gratification and (2) the degree of neural activation in the striatum, which plays a fundamental role in reward prediction and in time estimation, may code for the time delay.
即时奖励比在未来某个时间出现的相同奖励更有价值。为了研究这一过程背后的神经基础，我们对13名健康志愿者进行了研究，他们在事件相关功能磁共振成像期间使用延迟折扣任务，反复在即时奖励和参数变化的延迟假设奖励之间做出决定。受试者的偏好判断导致了较短（<1年）和较长（≥1年）延迟的不同折扣斜率。与较长延迟相比，与较短延迟相关的神经激活与左侧尾状核头部和壳核的激活增加有关。当个体选择延迟奖励而非即时奖励时，在双侧后岛叶皮质发现了强烈的激活。包括左侧尾状核在内的几个脑区显示，行为确定的折扣与<1年和≥1年延迟间隔对比的脑激活之间存在相关性。这些结果表明：（1）后岛叶作为决策神经网络的关键组成部分，参与了延迟满足；（2）在奖励预测和时间估计中起基本作用的纹状体中的神经激活程度可能编码了时间延迟。
