你的大脑能“招架”多少朋友？

Being a social butterfly just might change your brain: In people with a large network of friends and excellent social skills, certain brain regions are bigger and better connected than in people with fewer friends, a new study finds.

The research, presented here Tuesday (Nov. 12) at the annual meeting of the Society for Neuroscience, suggests a connection between social interactions and brain structure.

"We're interested in how your brain is able to allow you to navigate in complex social environments," study researcher MaryAnn Noonan, a neuroscientist at Oxford University, in England, said at a news conference. Basically, "how many friends can your brain handle?" Noonan said.

Scientists still don't understand how the brain manages human behavior in increasingly complex social situations, or what parts of the brain are linked to deviant social behavior associated with conditions like autismand schizophrenia.

Studies in macaque monkeys have shown that brain areas involved in face processing and in predicting the intentions of others are larger in animalsliving in large social groups than in ones living in smaller groups.

To investigate these brain differences in humans, Noonan and her colleagues at McGill University, in Canada, recruited 18 participants for a structural brain-imaging study. They asked people how many social interactions they had experienced in the past month, in order to determine the size of their social networks.

As was the case in monkeys, some brain areas were enlarged and better connectedin people with larger social networks. In humans, these areas were the temporal parietal junction, the anterior cingulate cortex and the rostral prefrontal cortex, which are part of a network involved in "mentalization"—the ability to attribute mental states, thoughts and beliefs to another.

"These different brain regions are all singing different songs," Noonan said. "Networked areas are all singing the same song, and when they're connected better, they're singing more harmoniously with each other."

The researchers also tested whether the size of a person's social networkwas linked with changes in white-matter pathways, the nerve fibers that connect different brain regions.

Again, they found that white-matter tracts were better connected in people with bigger social networks. "The nerves were more like a Los Angeles freeway than a country road," Noonan said.

The researchers couldn't say whether social interaction caused these changes in brain structure and connectivity, or whether the brain determined how innately social someone was.

In the case of the monkeys, the researchers dictated the size of the animals' social network, so they concluded that social-group size was causing the brain differences.

It can be inferred that a similar process takes place in human brains, but to prove this, long-term studies are needed, Noonan told LiveScience.

The fact that some brain regions may be larger and more connected suggests other regions might be smaller in the brains of the more socially adept, Noonan said.

"If you're spending a lot of time in social environments using social skills and your brain's changing, maybe you're not learning to juggle in your free time or becoming proficient at the piano," she said. "The brain is just changing and optimizing to reflect your needs, and if that is thriving within a complex social environment, that is what your brain is reflecting."

一项最新研究发现，成为一名“交际花”可能意味着改变你的大脑：比起朋友少的人，拥有庞大网友圈和杰出社交能力的人的特定大脑区域更大、联络更发达。

11月12日，该研究在神经科学学会的年会上提出，表明社会互动与大脑构造之间的联系。

“我们渴望知道你的大脑如何使你在复杂的社会环境中保持方向感，” 研究员努南在英国的记者招待会上说，她是一名牛津大学的神经学家。简言之，“你的大脑能 ‘招架’多少朋友？” 她说道。

科学家仍不清楚大脑是怎样在日趋复杂的社会环境下管理人类行为，或者说，大脑的哪个部分与异常社会行为有关联，比如孤独症和神经分裂症。

对于猕猴的研究表明，生活在大型社会群体中的猕猴参与面部识别、揣测他人意图的大脑功能区较大。

为研究人类大脑的这些差异，努南和她在加拿大麦吉尔大学的同事招募了18名参与者展开了一项结构性脑成像研究。他们询问参与者在过去的一个月内参与了多少社交活动，以确定他们社交网络的大小。

与猴子实验结果相符，拥有较大社交圈的人们通常有更大的、联络更发达的大脑。对人类而言，这些区域是颞顶叶交界处、前扣带皮质和侧前额叶皮层，这是部分参与实现“心理化”的神经系统——即分配精神状态、思想和信仰的能力。

“不同的大脑区域分工协作，” 努南说，“神经系统整体步调一致，并且当他们联络得更好时，这种协同合作更和谐。”

研究人员还测试了一个人的社交网络是否与白质通路的改变有关，也就是连接大脑不同区域的神经纤维。

再一次，他们发现拥有更大社交圈子的人的白质纤维束联络更为发达。“这些神经就像是一条洛杉矶超速干道而不是乡间小路。” 努南说。

研究人员还不能确认社会互动是否导致了大脑结构和连通性的改变，或者大脑是否决定了一个人与生俱来的社交能力的高低。

在猴子的案例中，研究者记录了动物的社交网络规模，因此得出结论，社会群体的大小导致了大脑的差异。

由此推测，人类大脑也经过了类似的过程，但是这仍需长期研究来证明，努南对“生活科学”网站说。

她表示，社交达人特定大脑区域更大、联络更发达的事实还暗示了他们大脑的其他区域可能会更小。

“如果你在社会环境中花很多时间交际，你的大脑就在改变，你可能不会了解平衡自己的空闲时间，或是精通钢琴，”她说，“大脑就是在优化改变以适应你的需要，如果你渴望复杂的社会环境，这恰恰就是你的大脑正在反映的。”