美国科学家在12月20日的《The Journal of Neuroscience》上发表文章，声称根据他们的大脑成像研究发现，人类大脑的奖赏机制具有变化的灵敏度，那些易受刺激影响的人们的大脑奖赏中心表现得最活跃。
??美国匹兹堡大学的Ahmad Hariri博士和同事们与他们在Mount Sinai医学院和芝加哥大学的合作者们，通过对45个研究对象的研究发现，大脑的重要奖赏回路部分——腹侧组织层（ventral striatum）的活动，与人的冲动有直接的关系。
??密歇根大学生物心理学计划的Terry E. Robinson博士说：“这些数据是令人激动的，因为这能够由个人复杂的心理结构，如‘冲动’，来区分个人大脑组织的不同。这也许会有助于研究上瘾的机理。”
??Hariri的小组通过两个计算机任务来对研究对象进行测试。首先，参与者们对一系列短期和长期的薪酬进行选择。他们或者选择当天得到10美分到105美元或者选择五年后得到100美元乘以七个点数之一。然后根据他们的选择计算出所谓的“转换点数”——使他们对当天拿到钱和在未来拿到钱同样满意的点数。
??七个月后，研究对象被告知如果他们能够正确地猜出一系列卡片上的数字就能够得到报酬，同时科学家们使用依赖血氧浓度变化(BOLD)的功能核磁共振（fMRI）来测量研究对象在回答正确和错误时的大脑活动。这些图像反映了参与者对正面和负面“奖赏”反馈的反应。然后通过把图像和研究对象的转换点数对应的冲动值相匹配，就得到了研究结果。
??结果表明，那些表现出强烈地直接酬金奖励偏爱的人的腹侧组织层对金钱奖励的正负反馈表现得最活跃。
??Hariri说：“我们的发现表明腹侧组织层在满意和延迟、冲动和谨慎之前的选择起了关键的作用。而这些选择对于我们现在和未来的安康具有深远的意义。”
英文原文：
Impulsiveness linked to activity in brain's reward center
A new imaging study shows that our brains react with varying sensitivity to reward and suggests that people most susceptible to impulse -- those who need to buy it, eat it, or have it, now -- show the greatest activity in a reward center of the brain. The study appears in the December 20 issue of The Journal of Neuroscience.
In their study of 45 subjects, Ahmad Hariri, PhD, and colleagues at the University of Pittsburgh and collaborators at Mount Sinai School of Medicine and the University of Chicago showed that activity in the ventral striatum, a core component of the brain's reward circuitry, correlated with individuals' impulsiveness.
"These data are exciting because they begin to unravel individual differences in brain organization underlying differences in complex psychological constructs, such as 'impulsivity,' which may contribute to the propensity to addiction," says Terry E. Robinson, PhD, of the University of Michigan biopsychology program.
The Hariri team tested the subjects on two computer-based tasks. First, participants indicated their preferences in a series of immediate-versus-delayed, hypothetical monetary rewards. They chose between receiving an amount from 10 cents to $105 that day and receiving $100 at one of seven points up to five years in the future. "Switch points"—the value at which they were equally likely to choose getting money today as getting $100 at a future point in time—were calculated for each person.
Seven months later, subjects were told they could win money if they correctly guessed numbers on a series of cards while scientists used blood oxygenation-level dependent (BOLD) functional magnetic resonance imaging (fMRI) to measure brain activity in response to correct and incorrect guesses. These images reflected participants' reactions to positive and negative "reward" feedback. After matching images to the subjects' switch points on the index of impulsiveness, the researchers looked for patterns.
Individuals indicating the strongest preference for immediate over delayed rewards showed the most ventral striatum activity associated with positive and negative feedback for a monetary reward.
"Our findings suggest that the ventral striatum plays a key role in striking a balance between gratification and delay, impulsive action and prudent choice, that can have far-reaching implications for our current and future well-being," says Hariri.
The team aims to examine the role of specific factors that drive the sensitivity of the ventral striatum next. One target of future research will be genes that regulate levels of the neurotransmitter dopamine and how they vary among individuals, Hariri says.
