What the Gay Brain Looks Like

What the Gay Brain Looks Like
Tuesday, Jun. 17, 2008 By ALICE PARK

What makes people gay? Biologists may never get a complete answer to that question, but researchers in Sweden have found one more sign that the answer lies in the structure of the brain.

Scientists at the Karolinska Institute studied brain scans of 90 gay and straight men and women, and found that the size of the two symmetrical halves of the brains of gay men more closely resembled those of straight women than they did straight men. In heterosexual women, the two halves of the brain are more or less the same size. In heterosexual men, the right hemisphere is slightly larger. Scans of the brains of gay men in the study, however, showed that their hemispheres were relatively symmetrical, like those of straight women, while the brains of homosexual women were asymmetrical like those of straight men. The number of nerves connecting the two sides of the brains of gay men were also more like the number in heterosexual women than in straight men.

Just what these brain differences mean is still not clear. Ever since 1991, when Simon LeVay first documented differences in the hypothalamus of gay and straight men, researchers have been struggling to understand what causes these differences to occur. Until now, the brain regions that scientists have come to believe play a role in sexual orientation have been related to either reproduction or sexuality. The Swedish study, however, is the first to find differences in parts of the brain not normally involved in reproduction — the denser network of nerve connections, for example, was found in the amygdala, known as the emotional center of the brain. "The big question has always been, if the brains of gay men are different, or feminized, as earlier research suggests," says Dr. Eric Vilain, professor of human genetics at University of California Los Angeles, "then is it just limited to sexual preference or are there other regions that are gender atypical in gay males? For the first time, in this study it looks like there are regions of the brain not directly involved in sexuality that seem to be feminized in gay males."

Vilain, who studies the genetic factors behind sexuality and sexual orientation, notes that it may turn out that the brains of gay men possess only some 'feminized' structures, while retaining some masculine ones, and this is reflected in how they act on their sexuality. "We know from studies that men, regardless of their sexual orientation, retain masculine characteristics when it comes to their sexual behavior," he says. Both gay and straight men, for example, tend to prefer younger partners, in contrast to women, who gravitate toward older partners. Most men are also more likely than women to engage in casual sex, and to be aroused by visual stimuli. "So I expect that some regions of the brain will remain masculine even in gay men," says Vilain. For something as complex as sexual orientation, it's no surprise that everything from genes to gender to environment may play a role in ultimately determining your perfect partner.

男“同志”的大脑是啥模样？

　　什么造就了男"同志"？生物学家恐怕永远不能给出完整的答案，但瑞典的研究人员找到了不止一个与其答案相关的大脑结构特点。
　　Karolinska研究院的科学家扫描了90位同性恋男性和异性恋男女性的大脑。他们发现，与异性恋男性相比，同性恋男性的大脑与异性恋女性更相似。异性恋女性的两个脑半球容量相近。异性恋男性的右脑容量大一些。同性恋男性的大脑扫描显示，他们的两个脑半球几乎对称，像异性恋女性一样。同样，同性恋女性的大脑与异性恋男性更相似。同性恋男性连接两个脑半球的神经数也更接近于异性恋女性。
　　这些脑结构上的差异说明了什么还不甚清晰。自从1991年Simon LeVay报告了男同性恋与男异性恋脑视丘下部的差异以来，研究人员一直在试图弄清这些差异产生的原因。直到现在，科学家认为与性取向相关的脑域基本上是与生殖或性别有联系的。瑞典的研究首次找到了与生殖基本无关的脑域上的区别--例如，在脑扁桃体里的密集神经被认为是大脑的情感中枢。"重要的问题是，如果如之前的研究所显示的那样，男同性恋的大脑是女性化的，那么，" UCLA人类基因学教授Eric Vilain博士说，"这些大脑上的差异只影响了性取向吗？男同性恋的大脑中有没有其他异常的脑域？瑞典的这项研究首次说明了，男同性恋大脑中与性别不直接相关的脑域也女性化了。"
　　研究基因对性别和性取向影响的Vilain博士还指出，男同性恋的大脑可能只包括部分女性化的结构，一些男性结构依然被保留，这点也通过男同性恋的性活动得到反映。"通过研究我们了解，不管是同性恋还是异性恋的男性，都在性行为中保留了男性特征，"他说。比如说，男同性恋和男异性恋都喜欢比自己年龄小的伴侣，而女性则喜欢年长的伴侣。大多数男性在性活动中更随意，更容易被视觉刺激所吸引。"因此我推测男同性恋的脑域中仍会保留男性特征，"Vilain说。对于性取向这种复杂的问题，完美伴侣的定义自然会受到基因、性别以及环境等多种因素的影响。