你的大腦能“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."一項最新研究發現，成爲一名“交際花”可能意味着改變你的大腦：比起朋友少的人，擁有龐大網友圈和傑出社交能力的人的特定大腦區域更大、聯絡更發達。

11月12日，該研究在神經科學學會的年會上提出，表明社會互動與大腦構造之間的聯繫。

“我們渴望知道你的大腦如何使你在複雜的社會環境中保持方向感，” 研究員努南在英國的記者招待會上說，她是一名牛津大學的神經學家。簡言之，“你的大腦能 ‘招架’多少朋友？” 她說道。

科學家仍不清楚大腦是怎樣在日趨複雜的社會環境下管理人類行爲，或者說，大腦的哪個部分與異常社會行爲有關聯，比如孤獨症和神經分裂症。

對於獼猴的研究表明，生活在大型社會羣體中的獼猴參與面部識別、揣測他人意圖的大腦功能區較大。

爲研究人類大腦的這些差異，努南和她在加拿大麥吉爾大學的同事招募了18名參與者展開了一項結構性腦成像研究。他們詢問參與者在過去的一個月內參與了多少社交活動，以確定他們社交網絡的大小。

與猴子實驗結果相符，擁有較大社交圈的人們通常有更大的、聯絡更發達的大腦。對人類而言，這些區域是顳頂葉交界處、前扣帶皮質和側前額葉皮層，這是部分參與實現“心理化”的神經系統——即分配精神狀態、思想和信仰的能力。

“不同的大腦區域分工協作，” 努南說，“神經系統整體步調一致，並且當他們聯絡得更好時，這種協同合作更和諧。”

研究人員還測試了一個人的社交網絡是否與白質通路的改變有關，也就是連接大腦不同區域的神經纖維。

再一次，他們發現擁有更大社交圈子的人的白質纖維束聯絡更爲發達。“這些神經就像是一條洛杉磯超速幹道而不是鄉間小路。” 努南說。

研究人員還不能確認社會互動是否導致了大腦結構和連通性的改變，或者大腦是否決定了一個人與生俱來的社交能力的高低。

在猴子的案例中，研究者記錄了動物的社交網絡規模，因此得出結論，社會羣體的大小導致了大腦的差異。

由此推測，人類大腦也經過了類似的過程，但是這仍需長期研究來證明，努南對“生活科學”網站說。

她表示，社交達人特定大腦區域更大、聯絡更發達的事實還暗示了他們大腦的其他區域可能會更小。

“如果你在社會環境中花很多時間交際，你的大腦就在改變，你可能不會了解平衡自己的空閒時間，或是精通鋼琴，”她說，“大腦就是在優化改變以適應你的需要，如果你渴望複雜的社會環境，這恰恰就是你的大腦正在反映的。”