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.

    不是性別歧視，但有一個問題：為什么女孩表現(xiàn)的更為女孩？

    過去半個世紀(jì)以來，女權(quán)主義者、反對者和學(xué)術(shù)界的人們討論了男女之間的巨大差別。 僅在過去幾年里，科學(xué)家一直在使用成像技術(shù)來研究男女的大腦，以研究不同性別人腦中存在區(qū)別的原因。然而，那些研究都沒有具體結(jié)論。但最近出現(xiàn)了一種新的核磁共振成像的方法，科學(xué)家以兒童提為研究對象，這為一些普遍的社會行為提供了至少幾種解釋：例如女孩們關(guān)心一對一的尤其是最要好朋友間的關(guān)系，而男孩更傾向于與其他男孩集體活動和競爭。

    這項研究是由全國精神衛(wèi)生研究所及喬治亞州立大學(xué)共同進(jìn)行的。研究以家長知情為前提：當(dāng)孩子進(jìn)入青春時，他們的注意力會有很大變化。 他們顯得更關(guān)注同齡人兒不是他們的家庭。

    那么這些年輕人的頭腦中到底發(fā)生了什么樣的變化呢？科學(xué)家要求年齡在8-17歲的34個健康的孩子看一些照片上其他40個男孩和女孩，來判斷他們是否想與他們在線互動。他們要求孩子在0-100（不感興趣-很有興趣）的范圍來評估這些照片�？茖W(xué)家告訴那些孩子他們的評分是給圖片中男孩和女孩的分?jǐn)?shù)，他們將安排這些孩子與他們所喜歡的同伴進(jìn)行網(wǎng)上聊天。聊天將被假定在兩周之后。

    在那天，志愿者被再次帶到實驗室。這次，當(dāng)研究人員向他們展示圖片時采用的是核磁共振成像的方法來監(jiān)測孩子們的大腦活。 參與者被問之圖片上的哪些孩子愿意與他們進(jìn)行互動。

    這是精心策劃的一個計劃：照片上是演員的孩子并沒有被安排聊天見面。研究測試?yán)�用欺騙的手段目的是為了探測當(dāng)參與者期望表現(xiàn)出潛在而強(qiáng)烈得互動參與興趣時頭腦中的反應(yīng)。這種研究設(shè)計是復(fù)雜的--用核磁共振成像的方法來研究實際的社會互動是很困難的--像這樣的實驗以前還從來沒有進(jìn)行過。

    結(jié)果表明，女孩從青春期初期到青春期后期的發(fā)展過程中，她們腦部的某些特定區(qū)域在她們面對潛在的社會交往時變得更加活躍。具體來說，當(dāng)一個年紀(jì)較大的女孩想要見到某個新的朋友時--她相信那個人同時也會對她有興趣--她的伏隔核（與獎賞和動機(jī)有關(guān)）,下丘腦（與荷爾蒙激素有關(guān)）,海馬（與社會學(xué)習(xí)有關(guān)）和腦島（與主觀感覺有關(guān)）的活動變得更加活躍。相比之下，男孩在同樣的情形時這些區(qū)域活動表現(xiàn)的沒有這樣活躍。事實上，男孩頭腦中這些區(qū)域的活動呈下降趨勢。

    看起來男孩似乎對一對一的互動交流并不像女孩那樣感興趣。先前的研究表明青春期的男孩更加關(guān)注集體內(nèi)部的競爭（像運動隊之間）.證據(jù)或許表明進(jìn)化形成了男性更易傾向集體中競爭的活動。他們學(xué)著為女性消除競爭對手--在這過程中，女性則學(xué)會了一對一的判斷--男性則成為給與后代強(qiáng)有力保護(hù)的父親。

    該研究的發(fā)起人似乎不愿意得出這樣的有關(guān)性別差異的結(jié)論。神經(jīng)學(xué)家丹尼爾派恩（提出了關(guān)于女孩情趣反應(yīng)更易理解的原因）說："還有許多其他不同的可能性的解釋".他說："女孩在早期就試圖記住她們[關(guān)于孩童時的照片] 早期所寫的東西也是可能的。你可以想象一個情節(jié)：女孩說，'噢，我曾寫過那個女孩的不好？' 而男孩卻很少這樣做。換句話說，男孩得思路比較直接，他們不像女孩，有復(fù)雜的想法。