Pardon the sexism, but a question: Why are girls so girly?

For the past half-century, feminists, their opponents and armies of academics have debated the differences between men and women. Only in the past few years have scientists been able to use imaging technology to look inside men's and women's heads to investigate whether those stereotypical gender differences have roots in the brain. No concrete results have emerged from these studies yet, but now a new functional magnetic resonance imaging (fMRI) study of children offers at least one explanation for some common tween social behaviors: girls are hardwired to care about one-on-one relationships with their BFFs (best friends forever), while the brains of boys are more attuned to group dynamics and competition with other boys.

The study, conducted by researchers at the National Institute of Mental Health (NIMH) and Georgia State University, begins with a premise that every parent of a tween knows: as kids emerge into puberty, their focus changes dramatically. They care less about their families and more about their peers.

So what's actually going on inside these young brains? Scientists asked 34 healthy kids, ages 8 to 17, to look at pictures of 40 other boys and girls and judge how much they would like to interact with them online. The kids were asked to rate those in the photos on a scale from 0 ("not interested at all") to 100 ("very interested"). The NIMH scientists told the kids that their ratings would be revealed to the boys and girls in the pictures, and the scientists said they would arrange online chats between the kids and those they liked. The chats were supposed to occur two weeks later.

On the appointed day, the study volunteers were once again brought into the NIMH lab. This time, researchers monitored the kids' brain activity using fMRI while showing them the same pictures. The participants were asked to guess which of the kids in the pictures (the same kids they had rated — and who, they believed, knew those ratings) would like to interact with them.

It was all an elaborate ruse: the kids in the photos were actors, and there were no chats arranged. The purpose of the deception was to look inside participants' heads when they were highly engaged in a potential social interaction. Partly because the study design was so complex — it's difficult to study actual social interactions on fMRI — no experiment like this had ever been conducted before.

The results suggest that as girls progress from early puberty to late adolescence, certain regions of their brains become more active when they face a potential social interaction. Specifically, when an older girl anticipates meeting someone new — someone she believes will be interested in her — her nucleus accumbens (which is associated with reward and motivation), hypothalamus (associated with hormone secretion), hippocampus (associated with social learning) and insula (associated with subjective feelings) all become more active. By contrast, boys in the same situation show no such increase in activity in these areas. In fact, the activity in their insula actually declines.

Boys, it seems, aren't as interested in one-on-one interactions as girls are. Previous research has shown that male adolescents instead become more focused on competition within larger groups (like between sports teams). Perhaps it's evidence that evolution has programmed boys to compete within large groups, so they can learn to eliminate rivals for women — and that girls have been programmed to judge, one-on-one, who would be the most protective father for offspring.

The authors of the study are reluctant to draw such broad conclusions about the gender disparities. "There are many different possible explanations," says NIMH neuroscientist Daniel Pine, who suggests a much more ordinary reason for the girls' more emotional response. "It might be possible that the girls are trying to remember what they wrote earlier [about the kids in the photos]," he says. "You can imagine a scenario where they say, 'Oh, did I write something bad about that girl?' Boys are simply doing that less." In other words, it may be that boys are cads because they're not wired to be any other way.

不是性别歧视，但有一个问题：为什么女孩表现的更为女孩？

过去半个世纪以来，女权主义者、反对者和学术界的人们讨论了男女之间的巨大差别。 仅在过去几年里，科学家一直在使用成像技术来研究男女的大脑，以研究不同性别人脑中存在区别的原因。然而，那些研究都没有具体结论。但最近出现了一种新的核磁共振成像的方法，科学家以儿童提为研究对象，这为一些普遍的社会行为提供了至少几种解释：例如女孩们关心一对一的尤其是最要好朋友间的关系，而男孩更倾向于与其他男孩集体活动和竞争。

这项研究是由全国精神卫生研究所及乔治亚州立大学共同进行的。研究以家长知情为前提：当孩子进入青春时，他们的注意力会有很大变化。 他们显得更关注同龄人儿不是他们的家庭。

那么这些年轻人的头脑中到底发生了什么样的变化呢？科学家要求年龄在8-17岁的34个健康的孩子看一些照片上其他40个男孩和女孩，来判断他们是否想与他们在线互动。他们要求孩子在0-100（不感兴趣-很有兴趣）的范围来评估这些照片。科学家告诉那些孩子他们的评分是给图片中男孩和女孩的分数，他们将安排这些孩子与他们所喜欢的同伴进行网上聊天。聊天将被假定在两周之后。

在那天，志愿者被再次带到实验室。这次，当研究人员向他们展示图片时采用的是核磁共振成像的方法来监测孩子们的大脑活。 参与者被问之图片上的哪些孩子愿意与他们进行互动。

这是精心策划的一个计划：照片上是演员的孩子并没有被安排聊天见面。研究测试利用欺骗的手段目的是为了探测当参与者期望表现出潜在而强烈得互动参与兴趣时头脑中的反应。这种研究设计是复杂的——用核磁共振成像的方法来研究实际的社会互动是很困难的——像这样的实验以前还从来没有进行过。

结果表明，女孩从青春期初期到青春期后期的发展过程中，她们脑部的某些特定区域在她们面对潜在的社会交往时变得更加活跃。具体来说，当一个年纪较大的女孩想要见到某个新的朋友时——她相信那个人同时也会对她有兴趣——她的伏隔核（与奖赏和动机有关），下丘脑（与荷尔蒙激素有关），海马（与社会学习有关）和脑岛（与主观感觉有关）的活动变得更加活跃。相比之下，男孩在同样的情形时这些区域活动表现的没有这样活跃。事实上，男孩头脑中这些区域的活动呈下降趋势。

看起来男孩似乎对一对一的互动交流并不像女孩那样感兴趣。先前的研究表明青春期的男孩更加关注集体内部的竞争（像运动队之间）。证据或许表明进化形成了男性更易倾向集体中竞争的活动。他们学着为女性消除竞争对手——在这过程中，女性则学会了一对一的判断——男性则成为给与后代强有力保护的父亲。

该研究的发起人似乎不愿意得出这样的有关性别差异的结论。神经学家丹尼尔派恩（提出了关于女孩情趣反应更易理解的原因）说：“还有许多其他不同的可能性的解释”。他说：“女孩在早期就试图记住她们[关于孩童时的照片] 早期所写的东西也是可能的。你可以想象一个情节:女孩说，'噢，我曾写过那个女孩的不好？' 而男孩却很少这样做。换句话说，男孩得思路比较直接，他们不像女孩，有复杂的想法。