Women's brains are different from men's
[1]Men and women show differences in behaviour because their brains are physically distinct organs, new research suggests. Male and female brains appear to be constructed from markedly different genetic blueprints.
[2]The differences in the circuitry1 that wires them up and the chemicals that transmit messages inside them are so great as to point to the conclusion that there is not just one kind of human brain, but two, according to recent neurological2 studies.
[3]Men may be from Mars and women may be from Venus, and since the American psychotherapist3 John Gray wrote his famous book, in 1992, on the idea, it has been a commonplace to think of men and women as being from different planets in terms of their emotional responses.
[4]But until recently, these differences were often explained by the action of adult sex hormones, or by social pressures that encouraged males and females to behave in a certain way.
[5]Increasingly, however, these assumptions are being challenged, according to a review of recent neurological research appearing in recent New Scientist magazine, and it is becoming clear that the brains of men and women show numerous anatomical4 differences.
[6]Some of these divergences, the review by Hannah Hoag suggests, could explain a number of mysteries, such as why men and women are prone to different mental health problems, why some drugs work well for one sex but have little effect on the other, and why chronic pain tends to affect women more than men.
[7]Although it has long been known that there were some male-female differences, it was thought they were confined to the hypothalamus5, the brain region involved in regulating food intake, fighting and the sex drive, among other things. But it is becoming clear that the relative sizes of many of the structures inside female brains are different from those of males.
[8]One study, by scientists at Harvard Medical School, found that parts of the frontal lobe6, which houses decision-making and problem-solving functions, were proportionally larger in women, as was the limbic cortex, which regulates emotions. Other studies have found that the hippocampus7, involved in short-term memory and spatial navigation, is also proportionally larger in women than in men – "perhaps surprisingly, given women's reputation as bad map readers" says the New Scientist review.
[9]Proportionally larger brain areas in men include the parietal cortex, which processes signals from the sensory organs and is involved in space perception, and the amygdala8, which controls emotions and social and sexual behaviour. "The mere fact that a structure is different in size suggests a difference in functional organisation," says Dr Larry Cahill of the Centre for the Neurobiology of Learning and Memory, at the University of California, Irvine.
[10]One area of research concerns the brain's pain-suppressing mechanisms, and points to the fact that they may be organised differently in men and women. This would explain why women can suffer long-term pain more, and why there can be sex differences in response to opium-derived painkilling drugs. The study notes: "Women get more relief from the opioid painkiller nalbuphine9 compared to men, whereas in men morphine is more effective and nalbuphine actually increases the pain intensity." It is possible these findings could lead to new painkillers being developed that are tailored to be more effective in women – but that is some way off10.
[11]Mental health is another area where real brain differences may offer explanations. Women are diagnosed with depression twice as often as men, and this may be linked to relative levels of the neurotransmitter serotonin. Boys, on the other hand, are more likely than girls to be diagnosed with autism, Tourette's syndrome11, dyslexia, attention-deficit disorder and early-onset schizophrenia. The review reports that Margaret McCarthy of the University of Maryland in Baltimore believes that hormone-like substances called prostaglandins, which help masculinise the male brain around the time of birth, may be partly to blame.
[12]One of the reasons why physiological differences between male and female brains have not been widely noted before may be that most of what we know about the brain comes from studies of males, animals and human volunteers.
[13]Professor Jeff Mogil from McGill University, in Montreal, Canada, who has demonstrated major differences in pain processing in males and females, puts it even more forcefully. He is astonished that so many researchers have failed to include female animals in their studies. "It's scandalous," he said. "Women are the most common pain sufferers, and yet our model for basic pain research is the male rat."
男女大腦有何不同
[1]最新研究表明，男女行為上表現出來的差異是因為他們的大腦是有著顯著不同的器官。男性與女性大腦看來似乎建構於明顯不同的基因藍圖。
[2]根據近期的神經學研究，連接他們大腦的腦電網絡與在大腦內部傳輸信息的化學物質差異巨大從而使人們得出結論-並不只有一種人類大腦，而是兩種。
[3]男人可能來自於火星，而女人則可能來自於金星。自從1992年美國心理治療專家約翰•格雷在他所寫的大名鼎鼎的著作中闡述了這一觀點之後，從情感回應方面說來，認為男性和女性來自於不同的行星便已成為老生常談之事。
[4]直到最近，這些不同還經常被解釋為是由於成年人性激素的作用或是社會壓力促使男性和女性按照某種既有的模式行事。
[5]然而根據《新科學家》雜誌上刊登的一篇近期神經學研究回顧文章，這些假設正逐漸受到挑戰。事實愈發清楚地表明男女大腦存在著諸多解剖差異。
[6]漢納·霍格寫的這篇回顧文章中指出這些差異中的一部分可用來解釋大量謎團。例如，男性和女性為何傾向於產生不同的心理健康問題，為何某些藥品對一種性別效果不錯，而對另外一種性別卻是收效甚微，為何慢性疼痛對女性的影響往往會多於男性。
[7]儘管男女有別早被人知，但此種認識只被局限於下丘腦——即專門用於調節食物攝取、爭鬥、性發育驅動的大腦區域。人們越來越清楚地認識到女性大腦中的許多構造的相對尺寸與男性的有所不同。
[8]從來自哈佛大學醫學院的科學家們所進行的一項研究中發現女性大腦前額葉中具有決策和解決問題功能的那些部分從比例上說要比男性大，調節情感的皮質邊緣也是如此。其它研究還發現，女性大腦中參與短時記憶和空間導向的海馬區也要比男性的大些-或許令人驚訝，《新科學家》雜誌中的回顧一文寫到 「女性被稱作糟糕的地圖識別者」 。
[9]按比例來說，男性比女性大的大腦結構包括頂葉皮質(負責處理來自於感知器官的信號並參與空間感知)和杏仁體(用於控制情感以及社會行為和性行為)。加州大學爾灣分校學習與記憶神經生物學中心的拉裡•卡西爾博士說，「一種結構在尺寸上的差異這一事實表明功能組織的不同。
[10]研究的一個領域涉及大腦的鎮痛機制，這一研究指出如下事實，即男性和女性的鎮痛機制組織不同。這些應該能解釋女性更能承受常時間疼痛的原因以及為什麼會有對鴉片類鎮痛藥物反應的性別差異。研究顯示：「和男性比起來，女性可以從鴉片類鎮痛藥納布芬中得到更多的緩解，但是對男性來說，嗎啡對鎮痛更有效而納布芬卻加重了疼痛。」這些發現可能導致開發出適用於女性更有效的新型止痛藥劑，但那任重而道遠。
[11]心理健康是真實的大腦差異可能提供解釋的另一個研究領域。女性被診斷為抑鬱症的數量是男性的二倍，這可能與神經傳遞介質血清素的相對水平有關。而另一方面男孩比女孩更易患自閉症、抽動症、失語症、注意力統合失調症以及早期攻擊精神分裂症。這份回顧文章報告說在巴爾的摩馬裡蘭大學的瑪格麗特·麥卡錫相信那些被叫做前列腺素的在出生前後促進男性大腦雄性化的激素類物質是導致這些疾病的部分原因。
[12]之所以以前人們沒有更多注意到男女大腦的生理差異，其中一個原因是我們所了解的絕大部分大腦知識都來自於對雄性動物及男性自願者的研究。
[13]加拿大蒙特婁麥卡吉爾大學的傑夫·摩澤爾教授已經演示了男女在疼痛感受上的主要差異，這使這項研究更有說服力。他很震驚，那麼多的研究者在研究中沒有包括雌性動物。他說：「這是可恥的。因為女性是最常見的疼痛承受者，而我們最基本的疼痛研究樣本是雌性鼠。」