How the brain responds to reward is linked to socioeconomic background

MIT neuroscientists have found that the brain’s sensitivity to rewarding experiences — a critical factor in motivation and attention — can be shaped by socioeconomic conditions.

麻省理工学院的神经科学家发现，大脑对奖励体验的敏感性（动机和注意力的关键因素）可能受到社会经济条件的影响。

In a study of 12 to 14-year-olds whose socioeconomic status (SES) varied widely, the researchers found that children from lower SES backgrounds showed less sensitivity to reward than those from more affluent backgrounds.

在一项针对社会经济地位 (SES) 差异很大的 12 至 14 岁儿童的研究中，研究人员发现，与来自较富裕背景的孩子相比，来自较低 SES 背景的孩子对奖励的敏感度较低。

Using functional magnetic resonance imaging (fMRI), the research team measured brain activity as the children played a guessing game in which they earned extra money for each correct guess. When participants from higher SES backgrounds guessed correctly, a part of the brain called the striatum, which is linked to reward, lit up much more than in children from lower SES backgrounds.

研究小组利用功能磁共振成像（fMRI）测量了孩子们玩猜谜游戏时的大脑活动，每猜对一次，他们就能赚到额外的钱。当来自较高社会经济地位背景的参与者猜对时，大脑中与奖励相关的称为纹状体的部分会比来自较低社会经济地位背景的儿童更加活跃。

The brain imaging results also coincided with behavioral differences in how participants from lower and higher SES backgrounds responded to correct guesses. The findings suggest that lower SES circumstances may prompt the brain to adapt to the environment by dampening its response to rewards, which are often scarcer in low SES environments.

大脑成像结果也与来自较低和较高社会经济地位背景的参与者对正确猜测的反应的行为差异相吻合。研究结果表明，较低社会经济地位的环境可能会通过抑制大脑对奖励的反应来促使大脑适应环境，而在低社会经济地位的环境中，奖励往往更稀缺。

“If you’re in a highly resourced environment, with many rewards available, your brain gets tuned in a certain way. If you’re in an environment in which rewards are more scarce, then your brain accommodates the environment in which you live. Instead of being overresponsive to rewards, it seems like these brains, on average, are less responsive, because probably their environment has been less consistent in the availability of rewards,” says John Gabrieli, the Grover Hermann Professor of Health Sciences and Technology, a Professor of brain and cognitive sciences, and a member of MIT's McGovern Institute for Brain Research.

“如果你处于一个资源丰富的环境中，有很多奖励，你的大脑就会以某种方式进行调整。如果你处于奖励更加稀缺的环境中，那么你的大脑就会适应你所生活的环境。格罗弗·赫尔曼健康科学与技术教授约翰·加布里埃利 (John Gabrieli) 表示：大脑和认知科学教授，麻省理工学院麦戈文大脑研究所成员。

Gabrieli and Rachel Romeo, a former MIT postdoc who is now an assistant professor in the Department of Human Development and Quantitative Methodology at the University of Maryland, are the senior authors of the study. MIT postdoc Alexandra Decker is the lead author of the paper, which appears today in the Journal of Neuroscience.

加布里埃利和前麻省理工学院博士后、现任马里兰大学人类发展和定量方法学系助理教授的雷切尔·罗密欧是该研究的资深作者。麻省理工学院博士后亚历山德拉·德克尔 (Alexandra Decker) 是这篇论文的主要作者，该论文今天发表在《神经科学杂志》上。

Previous research has shown that children from lower SES backgrounds tend to perform worse on tests of attention and memory, and they are more likely to experience depression and anxiety. However, until now, few studies have looked at the possible association between SES and reward sensitivity.

先前的研究表明，社会经济地位较低背景的儿童在注意力和记忆力测试中往往表现较差，而且他们更有可能经历抑郁和焦虑。然而，到目前为止，很少有研究探讨 SES 与奖励敏感性之间可能存在的关联。

In the new study, the researchers focused on a part of the brain called the striatum, which plays a significant role in reward response and decision-making. Studies in people and animal models have shown that this region becomes highly active during rewarding experiences.

在这项新研究中，研究人员重点研究了大脑中称为纹状体的部分，它在奖励反应和决策中发挥着重要作用。对人类和动物模型的研究表明，该区域在获得奖励的经历中变得高度活跃。

To investigate potential links between reward sensitivity, the striatum, and socioeconomic status, the researchers recruited more than 100 adolescents from a range of SES backgrounds, as measured by household income and how much education their parents received.

为了调查奖励敏感性、纹状体和社会经济地位之间的潜在联系，研究人员招募了 100 多名来自不同社会经济地位背景的青少年，以家庭收入和父母接受的教育程度来衡量。

Each of the participants underwent fMRI scanning while they played a guessing game. The participants were shown a series of numbers between 1 and 9, and before each trial, they were asked to guess whether the next number would be greater than or less than 5. They were told that for each correct guess, they would earn an extra dollar, and for each incorrect guess, they would lose 50 cents.

每个参与者在玩猜谜游戏时都接受了功能磁共振成像扫描。向参与者展示一系列 1 到 9 之间的数字，在每次试验之前，他们被要求猜测下一个数字是否大于或小于 5。他们被告知，每猜对一次，他们将获得额外的奖励美元，每猜错一次，他们就会损失 50 美分。

Unbeknownst to the participants, the game was set up to control whether the guess would be correct or incorrect. This allowed the researchers to ensure that each participant had a similar experience, which included periods of abundant rewards or few rewards. In the end, everyone ended up winning the same amount of money (in addition to a stipend that each participant received for participating in the study).

参与者不知道的是，游戏的设置是为了控制猜测是否正确。这使得研究人员能够确保每个参与者都有相似的经历，其中包括奖励丰富或奖励很少的时期。最后，每个人都赢得了相同数额的钱（除了每个参与者因参与研究而获得的津贴）。

Previous work has shown that the brain appears to track the rate of rewards available. When rewards are abundant, people or animals tend to respond more quickly because they don’t want to miss out on the many available rewards. The researchers saw that in this study as well: When participants were in a period when most of their responses were correct, they tended to respond more quickly.

之前的研究表明，大脑似乎会追踪可用奖励的比率。当奖励丰富时，人或动物往往会做出更快的反应，因为他们不想错过许多可用的奖励。研究人员在这项研究中也发现：当参与者处于大多数反应都是正确的时期时，他们往往会做出更快的反应。

“If your brain is telling you there's a really high chance that you're going to receive a reward in this environment, it's going to motivate you to collect rewards, because if you don't act, you're missing out on a lot of rewards,” Decker says.

“如果你的大脑告诉你，在这种环境下你获得奖励的机会非常高，它就会激励你去收集奖励，因为如果你不采取行动，你就会错过很多东西奖励，”德克尔说。

Brain scans showed that the degree of activation in the striatum appeared to track fluctuations in the rate of rewards across time, which the researchers think could act as a motivational signal that there are many rewards to collect. The striatum lit up more during periods in which rewards were abundant and less during periods in which rewards were scarce. However, this effect was less pronounced in the children from lower SES backgrounds, suggesting their brains were less attuned to fluctuations in the rate of reward over time.

大脑扫描显示，纹状体的激活程度似乎可以追踪奖励率随时间的波动，研究人员认为这可以作为一种激励信号，表明有很多奖励可以收集。在奖励丰富的时期，纹状体的亮度较高，而在奖励稀缺的时期，纹状体的亮度则较少。然而，这种效应在社会经济地位较低背景的儿童中不太明显，这表明他们的大脑不太适应奖励率随时间的波动。

The researchers also found that during periods of scarce rewards, participants tended to take longer to respond after a correct guess, another phenomenon that has been shown before. It’s unknown exactly why this happens, but two possible explanations are that people are savoring their reward or that they are pausing to update the reward rate. However, once again, this effect was less pronounced in the children from lower SES backgrounds — that is, they did not pause as long after a correct guess during the scarce-reward periods.

研究人员还发现，在奖励稀缺的时期，参与者在正确猜测后往往需要更长的时间才能做出反应，这是之前已经出现过的另一个现象。目前尚不清楚为什么会发生这种情况，但有两种可能的解释是，人们正在享受奖励，或者他们正在停下来更新奖励率。然而，这种效应在社会经济地位较低背景的孩子中并不那么明显——也就是说，在稀缺奖励期间，他们在正确猜测后并没有停顿那么长时间。

“There was a reduced response to reward, which is really striking. It may be that if you’re from a lower SES environment, you’re not as hopeful that the next response will gain similar benefits, because you may have a less reliable environment for earning rewards,” Gabrieli says. “It just points out the power of the environment. In these adolescents, it’s shaping their psychological and brain response to reward opportunity.”

“人们对奖励的反应有所减少，这确实令人震惊。如果你来自社会经济地位较低的环境，你可能不太希望下一次响应会获得类似的好处，因为你可能有一个不太可靠的环境来获得奖励，”加布里埃利说。“它只是指出了环境的力量。在这些青少年中，它正在塑造他们的心理和大脑对奖励机会的反应。”

The fMRI scans performed during the study also revealed that children from lower SES backgrounds showed less activation in the striatum when they guessed correctly, suggesting that their brains have a dampened response to reward.

研究期间进行的功能磁共振成像扫描还显示，来自较低社会经济背景的儿童在猜对时纹状体的激活程度较低，这表明他们的大脑对奖励的反应减弱。

The researchers hypothesize that these differences in reward sensitivity may have evolved over time, in response to the children’s environments.

研究人员推测，奖励敏感性的这些差异可能随着时间的推移而演变，以适应儿童的环境。

“Socioeconomic status is associated with the degree to which you experience rewards over the course of your lifetime,” Decker says. “So, it’s possible that receiving a lot of rewards perhaps reinforces behaviors that make you receive more rewards, and somehow this tunes the brain to be more responsive to rewards. Whereas if you are in an environment where you receive fewer rewards, your brain might become, over time, less attuned to them.”

“社会经济地位与你一生中获得回报的程度有关，”德克尔说。“因此，接受大量奖励可能会强化行为，使你获得更多奖励，并且以某种方式调整大脑，使其对奖励更加敏感。然而，如果你处于一个获得较少奖励的环境中，随着时间的推移，你的大脑可能会变得不太适应它们。”

The study also points out the value of recruiting study subjects from a range of SES backgrounds, which takes more effort but yields important results, the researchers say.

研究人员表示，该研究还指出了从各种社会经济地位背景中招募研究对象的价值，这需要付出更多的努力，但会产生重要的结果。

“Historically, many studies have involved the easiest people to recruit, who tend to be people who come from advantaged environments. If we don’t make efforts to recruit diverse pools of participants, we almost always end up with children and adults who come from high-income, high-education environments,” Gabrieli says. “Until recently, we did not realize that principles of brain development vary in relation to the environment in which one grows up, and there was very little evidence about the influence of SES.”

“从历史上看，许多研究都涉及最容易招募的人，他们往往是来自有利环境的人。如果我们不努力招募不同的参与者，我们最终几乎总是来自高收入、高教育环境的儿童和成人，”加布里埃利说。“直到最近，我们才意识到大脑发育的原理会随着成长环境的变化而变化，而且几乎没有证据表明 SES 的影响。”

The research was funded by the William and Flora Hewlett Foundation and a Natural Sciences and Engineering research Council of Canada Postdoctoral Fellowship.

该研究由威廉和弗洛拉·休利特基金会以及加拿大自然科学和工程研究委员会博士后奖学金资助。