大脑也有性别差异？

即使是一些陈词滥调也提示了一些真理性的东西。众所周知男人生气时比较容易大喊大叫或者捶打墙壁，而女人生气时则比较容易会静坐着生闷气，不易向外发泄。这些又给我们提示了什么？最近一项研究显示，大脑杏仁核存在的内在差异决定影响男人与女人处事方式（包括情感反应）。研究显示不但杏仁核的结构及功能存在性别差异，而且在杏仁核的活性与大脑其它区的协调作用方面男性与女性存在差别。

杏仁核跨大脑左右半球，其功能在于帮助人们控制情感反应如恐惧等如何进行及被记忆。多项研究发现杏仁核被激活时存在性差异。在一项研究中，叫志愿者回忆恐怖电影，在男性志愿者中，右杏仁核变得更活跃。而在女生则表现为左杏仁核更活跃。加州大学神经生物学家Larry Cahill想知道杏仁核表现的上述性别差异是否为硬线性的，即想弄清楚甚至在没有什么事情激活它的时候，杏仁核是否保持这种性别特异性倾向。如果答案是肯定的，那么这将提示男性与女性杏仁核存在固有的差异。Cahill及其同事研究了36名男性和36名女性（男性与女性志愿者皆为右利手的）的PET扫描资料。PET扫描时要求志愿者闭上双眼处于放松休息状态。他们发现，即使在休息状态，男性与女性杏仁核工作存在差异。在女生，左杏仁核血流量伴随大脑其它区血流量衰减及充盈，而右杏仁核极小有如此现象。而在男性，则表现为右杏仁核血流量改变伴随大脑其它区血流量变化。

更有有趣的发现在于与杏仁核协调作用的区域的差异。在女生，这些区域似乎是下丘脑及有关的皮质下区，而下丘脑的作用在于调控人体的应激反应及情感反应。而在男性，杏仁核协调作用于大脑的有关运动及视觉区，运运区及视觉区被认为是在与外部世界反应发挥重要作用。研究者在2006年4月7日NeuroImage报道了他们的发现。对于此项发现，神经科学家John Gabrieli认为，对于男性来说，似乎存在更强的协调性以便处理处界事物。但目前人们还不能确切理解这些确实存在的差异内在意义。

原文出处：Jennifer Couzin　　ScienceNOW Daily News 7 April 2006
原始文献:

A "His" or "Hers" Brain Structure?

By Jennifer Couzin
ScienceNOW Daily News
7 April 2006

Even oft-repeated gender stereotypes harbor some truth: Angry men are more likely to yell or punch a wall, whereas angry women sit silently stewing. Now, a new study is tracing these distinctions in how men and women process emotion to an almond-shaped structure deep in the brain. Not only does the structure, the amygdala, function differently by gender, but its activity in men is also coupled with very different brain regions than it is in women.

The amygdala straddles both sides of the brain and helps control how emotions such as fear are processed and remembered. Several studies have found gender differences when the amygdala is stimulated--by having volunteers recall scary movies, for example. In men, the right side of the amygdala, known simply as the right amygdala, appears more likely to become active, whereas in women it's the left. Neurobiologist Larry Cahill of the University of California, Irvine, wondered whether this difference was hardwired--whether, in other words, the amygdala retained its gender-specific tendencies even when nothing was activating it. If so, this would suggest that the structure was inherently different in men than in women.

Cahill and his colleagues studied PET scans of 36 men and 36 women, all of whom were right-handed. The scans had been collected for various brain studies where volunteers were asked to close their eyes and relax while the pictures were taken. The team found that, even at rest, the amygdala worked differently in men and women. In women, blood flow to the left amygdala ebbed and flowed along with other brain structures while the right amygdala did little. In men, it was blood flow to the right amygdala that varied along with blood flow elsewhere in the brain, the researchers report 1 April NeuroImage.

Especially intriguing, says Cahill, were the regions with which the amygdala was acting in concert. In women, those tended to be the hypothalamus, which directs the body's stress response and affects feelings, and the related subgenual cortex. In men, the amygdala acted with motor and visual brain areas, which are "believed important for interacting with the external world," says Cahill. He admits he doesn't know what the volunteers were thinking while being scanned or whether that affected the results.

Still, the study suggests that "this might be a default state," says John Gabrieli, a neuroscientist at the Massachusetts Institute of Technology in Cambridge. For men, he says, "it seems that there's a stronger coupling ... [for] dealing with stuff out there in the world," while this wasn't shown for women. No one knows quite what it all means, Gabrieli admits, but the findings are "food for thought."