Brain Research:发现时间折扣神经机制新证据
作者: 心理学 / 3428次阅读 时间: 2011年4月04日
来源: 转载
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年终将至,很多人都会拿到一笔年终奖或花红。假设你现在有一笔5000元的奖金,你可以做两个不同选择:选择一是现在就拿到5000元奖金(可以去好好消费犒劳自己一年的辛苦);选择二是把这些奖金存起来或投资,一年后可以得到5500元。请问你会选择哪一种?

我们先把这个问题放一下,考虑另外一种情景。现在使用信用卡的人越来越多,假设你上个月刷卡消费了5000元,今天是本月的还款日,你可以做两个不同选择:选择一是现在就还款5000元;选择二是付出一些利息,一年以后还款5500元。请问你会选择哪一种?

上述两个问题都是经济学中时间折扣(time discounting)的典型场景。顾名思义,时间折扣就是指人们会将未来获益或损失的价值打一个折扣,未来的权重低于对目前的权重。人类与动物的一个重要差异是,人类具有对未来进行计划和规划的能力。但在对未来与现在的价值进行权衡时——即跨期选择(intertemporal choice)时,如同故事“朝三暮四”中的猴子一样,人类难以避免地带有来自进化的非理性偏差:偏好即刻的价值胜于未来的更大价值。从动物到人类,从儿童到成人,这一普遍现象已被大量经济学和心理学研究所证实。近两年来,时间折扣又成为神经经济学(Neuroeconomics)领域中的一个热点和重要研究问题。

行为决策领域的研究已经证明,在面对损失或者获得的跨期选择时,人们对未来获得的时间折扣率大于对损失的折扣率,这被叫做符号效应(sign effect)。基于这一现象,中科院自动化所蒋田仔研究员、徐丽娟、王坤博士与中科院心理所李纾研究员、梁竹苑博士后,合作进行了一项fMRI研究,首次考察并比较了获得与损失领域中时间折扣的神经机制。

该研究巧妙地采用了获得与损失完全对等的实验设计,要求被试对类似上述两个情景(获得或损失)的一对选项进行选择。研究发现,在对获得和损失的时间折扣中,对获得和损失进行折扣的神经机制并不对称。一般来说,当被试对未来的获得与损失进行选择时,侧额叶和后顶叶区域都发生了激活,但在折扣损失时,不仅这两个区域的脑激活更强,脑岛、丘脑、背侧纹状体等区域也显著激活;而如果被试需要对即刻的选项进行选择,后扣带回和内侧前额叶皮质都会发生激活,但在折扣损失时,前扣带回、脑岛和额上回都会发生激活。这些结果说明,人类的大脑对未来损失比对未来的获得更加敏感,而这可能是由诸如恐惧、厌恶之类的负性情绪所驱动的。这一研究结果为揭开时间折扣的神经机制提供了新的证据。

这项研究由中科院心理研究所社会与经济行为研究中心李纾研究员与中科院自动化所蒋田仔研究员合作完成。为充分发挥双方在行为决策和神经影像领域的优势背景,双方自2006年开始神经经济学领域的合作研究。经过两年的耕耘,合作研究已开始收获喜人果实。根据上述研究结果撰写的研究报告,近期已在线发表在SCI索引期刊Brain Research。后续研究成果正在撰写中。

生物谷推荐原始出处:

Brain Research, In Press, Accepted Manuscript, Available online 6 January 2009

Neural Mechanism of Intertemporal Choice: From Discounting Future Gains to Future Losses

Lijuan Xu, Zhu-Yuan Liang, Kun Wang, Shu Li, Tianzi Jiang

Intertemporal choice, the tradeoff among outcomes occurring at different points in time, involves not only benefit options but also those associated with cost. Previous neuroimaging studies have primarily focused on discounting future gains; thus the neural mechanism underlying discounting future losses remains unidentified. Using event-related functional magnetic resonance imaging, we comprehensively investigated the neural mechanism of temporal discounting using two decision-making tasks with a symmetric pattern of gains and losses. Our results revealed that the lateral prefrontal and posterior parietal areas were activated in discounting both future gains and future losses, but their activations were stronger when discounting losses. Moreover, we found that the insula, thalamus and dorsal striatum were more activated during intertemporal choices involving losses, suggesting that the enhanced sensitivity to losses may be driven by negative emotions. In addition, whereas the posterior cingulate cortex and medial prefrontal cortex were activated when the choices included immediate options, extra regions including the anterior cingulate cortex, insula and superior frontal gyrus were preferentially activated when the choices involved immediate losses. Taken together, our findings suggest that a fronto-parietal network supports the common discounting process, and more importantly, discounting future losses and gains occurs asymmetrically in the brain. We speculate that this may provide a neural basis for the phenomenon that future losses are discounted less steeply than future gains.

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